head	1.168;
access;
symbols
	PTH_2_0_7:1.167
	PTH_2_0_6:1.166
	PTH_2_0_5:1.166
	PTH_2_0_4:1.166
	PTH_2_0_3:1.165
	PTH_2_0_2:1.163
	PTH_2_0_1:1.163
	PTH_2_0_0:1.162
	PTH_2_0b2:1.161
	PTH_2_0b1:1.161
	PTH_2_0b0:1.160
	PTH_1_4:1.151.0.2
	PTH_1_4_1:1.151
	PTH_1_4_0:1.145
	PTH_1_3_7:1.135
	PTH_1_4a3:1.138
	PTH_1_3_6:1.135
	PTH_1_4a2:1.137
	PTH_1_3_5:1.135
	PTH_1_4a1:1.137
	PTH_1_3_4:1.135
	PTH_1_3:1.135.0.2
	PTH_1_3_3:1.135
	PTH_1_3_2:1.132
	PTH_1_3_1:1.131
	PTH_1_3_0:1.130
	PTH_1_3b3:1.127
	PTH_1_2_3:1.112.2.3
	PTH_1_3b2:1.126
	PTH_1_3b1:1.120
	PTH_1_3a5:1.119
	PTH_1_3a4:1.118
	PTH_1_3a3:1.118
	PTH_1_2_2:1.112.2.2
	PTH_1_3a2:1.117
	PTH_1_2_1:1.112.2.1
	PTH_1_3a1:1.114
	PTH_1_2:1.112.0.2
	PTH_1_2_0:1.112
	PTH_1_2b8:1.110
	PTH_1_2b7:1.109
	PTH_1_1_6:1.104.2.1
	PTH_1_2b6:1.107
	PTH_1_2b5:1.107
	PTH_1_2b4:1.106
	PTH_1_2b3:1.106
	PTH_1_2b2:1.104
	PTH_1_2b1:1.104
	PTH_1_1_5:1.104
	PTH_1_0_6:1.94.2.1
	PTH_1_0_5:1.94
	PTH_1_0:1.94.0.2
	PTH_1_1:1.104.0.2
	PTH_1_1_4:1.104
	PTH_1_1_3:1.104
	PTH_1_1_2:1.104
	PTH_1_1_1:1.103
	PTH_1_1_0:1.102
	PTH_1_1b7:1.100
	PTH_1_1b6:1.100
	PTH_1_1b5:1.99
	PTH_1_1b4:1.98
	PTH_1_1b3:1.98
	PTH_1_1b2:1.98
	PTH_1_1b1:1.98
	PTH_1_0_4:1.94
	PTH_1_0_3:1.93
	PTH_1_0_2:1.90
	PTH_1_0_1:1.87
	PTH_1_0_0:1.85
	PTH_1_0b8:1.81
	PTH_1_0b7:1.81
	PTH_1_0b6:1.81
	PTH_1_0b5:1.80
	PTH_1_0b4:1.75
	PTH_1_0b3:1.68
	PTH_1_0b2:1.66
	PTH_1_0b1:1.59
	PTH_0_9_21:1.52
	PTH_0_9_20:1.50
	PTH_0_9_19:1.43
	PTH_0_9_18:1.37
	PTH_0_9_17:1.32
	PTH_0_9_16:1.32
	PTH_0_9_15:1.29
	PTH_0_9_14:1.27
	PTH_0_9_13:1.26
	PTH_0_9_12:1.24
	PTH_0_9_11:1.23
	PTH_0_9_10:1.23
	PTH_0_9_9:1.23
	PTH_0_9_8:1.17
	PTH_0_9_7:1.7
	PTH_0_9_6:1.6
	PTH_0_9_5:1.4
	PTH_0_9_4:1.4
	PTH_0_9_3:1.3
	PTH_0_9_2:1.3
	PTH_0_9_1:1.3
	PTH_0_9_0:1.1.1.1
	RSE:1.1.1;
locks; strict;
comment	@# @;


1.168
date	2007.01.01.18.23.52;	author rse;	state Exp;
branches;
next	1.167;
commitid	9DhdiirNzQPBIP0s;

1.167
date	2006.06.08.17.54.52;	author rse;	state Exp;
branches;
next	1.166;
commitid	x8N3mLVdQgkbdeAr;

1.166
date	2004.12.31.19.34.44;	author rse;	state Exp;
branches;
next	1.165;

1.165
date	2004.12.03.16.21.08;	author rse;	state Exp;
branches;
next	1.164;

1.164
date	2004.10.08.16.17.02;	author rse;	state Exp;
branches;
next	1.163;

1.163
date	2004.07.13.10.50.49;	author rse;	state Exp;
branches;
next	1.162;

1.162
date	2003.01.01.15.49.11;	author rse;	state Exp;
branches;
next	1.161;

1.161
date	2002.11.08.16.05.55;	author rse;	state Exp;
branches;
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1.160
date	2002.11.05.19.39.09;	author rse;	state Exp;
branches;
next	1.159;

1.159
date	2002.11.03.11.15.04;	author rse;	state Exp;
branches;
next	1.158;

1.158
date	2002.11.03.09.59.33;	author rse;	state Exp;
branches;
next	1.157;

1.157
date	2002.10.25.11.56.16;	author rse;	state Exp;
branches;
next	1.156;

1.156
date	2002.10.23.14.04.00;	author rse;	state Exp;
branches;
next	1.155;

1.155
date	2002.10.23.13.55.49;	author rse;	state Exp;
branches;
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1.154
date	2002.10.15.20.34.22;	author rse;	state Exp;
branches;
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1.153
date	2002.04.27.11.18.57;	author rse;	state Exp;
branches;
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1.152
date	2002.01.30.12.54.24;	author rse;	state Exp;
branches;
next	1.151;

1.151
date	2002.01.27.11.03.40;	author rse;	state Exp;
branches;
next	1.150;

1.150
date	2002.01.17.12.29.33;	author rse;	state Exp;
branches;
next	1.149;

1.149
date	2001.11.26.20.08.30;	author rse;	state Exp;
branches;
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1.148
date	2001.08.06.17.35.38;	author rse;	state Exp;
branches;
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1.147
date	2001.07.12.07.20.04;	author rse;	state Exp;
branches;
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1.146
date	2001.03.27.15.34.29;	author rse;	state Exp;
branches;
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1.145
date	2001.03.24.14.51.04;	author rse;	state Exp;
branches;
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1.144
date	2001.03.24.13.49.06;	author rse;	state Exp;
branches;
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1.143
date	2000.10.03.09.26.47;	author rse;	state Exp;
branches;
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1.142
date	2000.09.30.08.00.18;	author rse;	state Exp;
branches;
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1.141
date	2000.08.18.08.47.51;	author rse;	state Exp;
branches;
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1.140
date	2000.08.18.08.35.29;	author rse;	state Exp;
branches;
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1.139
date	2000.08.01.06.13.15;	author rse;	state Exp;
branches;
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1.138
date	2000.07.10.06.12.34;	author rse;	state Exp;
branches;
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1.137
date	2000.03.23.15.54.50;	author rse;	state Exp;
branches;
next	1.136;

1.136
date	2000.03.12.19.13.42;	author rse;	state Exp;
branches;
next	1.135;

1.135
date	2000.03.10.09.32.38;	author rse;	state Exp;
branches;
next	1.134;

1.134
date	2000.03.09.12.13.24;	author rse;	state Exp;
branches;
next	1.133;

1.133
date	2000.03.03.15.42.10;	author rse;	state Exp;
branches;
next	1.132;

1.132
date	2000.02.24.12.35.00;	author rse;	state Exp;
branches;
next	1.131;

1.131
date	2000.02.20.11.42.45;	author rse;	state Exp;
branches;
next	1.130;

1.130
date	2000.02.17.16.58.39;	author rse;	state Exp;
branches;
next	1.129;

1.129
date	2000.02.15.07.43.14;	author rse;	state Exp;
branches;
next	1.128;

1.128
date	2000.02.15.07.41.36;	author rse;	state Exp;
branches;
next	1.127;

1.127
date	2000.02.13.17.24.02;	author rse;	state Exp;
branches;
next	1.126;

1.126
date	2000.01.27.17.59.23;	author rse;	state Exp;
branches;
next	1.125;

1.125
date	2000.01.27.17.48.19;	author rse;	state Exp;
branches;
next	1.124;

1.124
date	2000.01.27.16.09.39;	author rse;	state Exp;
branches;
next	1.123;

1.123
date	2000.01.27.13.55.54;	author rse;	state Exp;
branches;
next	1.122;

1.122
date	2000.01.27.12.53.01;	author rse;	state Exp;
branches;
next	1.121;

1.121
date	2000.01.26.13.06.38;	author rse;	state Exp;
branches;
next	1.120;

1.120
date	2000.01.26.10.02.26;	author rse;	state Exp;
branches;
next	1.119;

1.119
date	2000.01.13.07.23.36;	author rse;	state Exp;
branches;
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1.118
date	2000.01.07.22.35.49;	author rse;	state Exp;
branches;
next	1.117;

1.117
date	99.12.30.21.58.59;	author rse;	state Exp;
branches;
next	1.116;

1.116
date	99.12.17.07.30.57;	author rse;	state Exp;
branches;
next	1.115;

1.115
date	99.11.09.08.11.31;	author rse;	state Exp;
branches;
next	1.114;

1.114
date	99.11.03.13.09.53;	author rse;	state Exp;
branches;
next	1.113;

1.113
date	99.11.01.10.27.18;	author rse;	state Exp;
branches;
next	1.112;

1.112
date	99.10.31.14.53.48;	author rse;	state Exp;
branches
	1.112.2.1;
next	1.111;

1.111
date	99.10.31.11.46.12;	author rse;	state Exp;
branches;
next	1.110;

1.110
date	99.10.26.14.24.27;	author rse;	state Exp;
branches;
next	1.109;

1.109
date	99.10.19.12.46.39;	author rse;	state Exp;
branches;
next	1.108;

1.108
date	99.10.03.17.49.15;	author rse;	state Exp;
branches;
next	1.107;

1.107
date	99.09.19.09.44.54;	author rse;	state Exp;
branches;
next	1.106;

1.106
date	99.09.17.08.11.09;	author rse;	state Exp;
branches;
next	1.105;

1.105
date	99.09.17.08.01.54;	author rse;	state Exp;
branches;
next	1.104;

1.104
date	99.08.23.12.00.53;	author rse;	state Exp;
branches
	1.104.2.1;
next	1.103;

1.103
date	99.08.20.07.17.08;	author rse;	state Exp;
branches;
next	1.102;

1.102
date	99.08.19.15.08.52;	author rse;	state Exp;
branches;
next	1.101;

1.101
date	99.08.19.14.37.42;	author rse;	state Exp;
branches;
next	1.100;

1.100
date	99.08.18.12.59.33;	author rse;	state Exp;
branches;
next	1.99;

1.99
date	99.08.17.09.02.10;	author rse;	state Exp;
branches;
next	1.98;

1.98
date	99.08.03.12.56.35;	author rse;	state Exp;
branches;
next	1.97;

1.97
date	99.08.03.12.42.48;	author rse;	state Exp;
branches;
next	1.96;

1.96
date	99.08.03.12.28.42;	author rse;	state Exp;
branches;
next	1.95;

1.95
date	99.08.03.12.24.02;	author rse;	state Exp;
branches;
next	1.94;

1.94
date	99.08.01.14.07.17;	author rse;	state Exp;
branches
	1.94.2.1;
next	1.93;

1.93
date	99.07.30.07.13.59;	author rse;	state Exp;
branches;
next	1.92;

1.92
date	99.07.30.07.06.38;	author rse;	state Exp;
branches;
next	1.91;

1.91
date	99.07.28.16.08.37;	author rse;	state Exp;
branches;
next	1.90;

1.90
date	99.07.25.08.38.53;	author rse;	state Exp;
branches;
next	1.89;

1.89
date	99.07.24.13.16.17;	author rse;	state Exp;
branches;
next	1.88;

1.88
date	99.07.23.13.39.42;	author rse;	state Exp;
branches;
next	1.87;

1.87
date	99.07.22.15.49.05;	author rse;	state Exp;
branches;
next	1.86;

1.86
date	99.07.22.14.55.09;	author rse;	state Exp;
branches;
next	1.85;

1.85
date	99.07.16.14.52.19;	author rse;	state Exp;
branches;
next	1.84;

1.84
date	99.07.16.11.40.11;	author rse;	state Exp;
branches;
next	1.83;

1.83
date	99.07.16.11.31.58;	author rse;	state Exp;
branches;
next	1.82;

1.82
date	99.07.16.11.15.57;	author rse;	state Exp;
branches;
next	1.81;

1.81
date	99.07.12.13.46.01;	author rse;	state Exp;
branches;
next	1.80;

1.80
date	99.07.11.15.39.39;	author rse;	state Exp;
branches;
next	1.79;

1.79
date	99.07.10.15.14.47;	author rse;	state Exp;
branches;
next	1.78;

1.78
date	99.07.10.14.21.17;	author rse;	state Exp;
branches;
next	1.77;

1.77
date	99.07.09.08.06.41;	author rse;	state Exp;
branches;
next	1.76;

1.76
date	99.07.08.15.01.17;	author rse;	state Exp;
branches;
next	1.75;

1.75
date	99.07.08.10.39.39;	author rse;	state Exp;
branches;
next	1.74;

1.74
date	99.07.08.10.34.00;	author rse;	state Exp;
branches;
next	1.73;

1.73
date	99.07.08.10.22.33;	author rse;	state Exp;
branches;
next	1.72;

1.72
date	99.07.08.10.20.05;	author rse;	state Exp;
branches;
next	1.71;

1.71
date	99.07.08.10.19.10;	author rse;	state Exp;
branches;
next	1.70;

1.70
date	99.07.08.10.17.03;	author rse;	state Exp;
branches;
next	1.69;

1.69
date	99.07.08.09.41.00;	author rse;	state Exp;
branches;
next	1.68;

1.68
date	99.07.07.19.02.28;	author rse;	state Exp;
branches;
next	1.67;

1.67
date	99.07.04.15.39.12;	author rse;	state Exp;
branches;
next	1.66;

1.66
date	99.07.04.13.00.51;	author rse;	state Exp;
branches;
next	1.65;

1.65
date	99.07.04.12.05.35;	author rse;	state Exp;
branches;
next	1.64;

1.64
date	99.07.04.12.01.43;	author rse;	state Exp;
branches;
next	1.63;

1.63
date	99.07.04.11.04.52;	author rse;	state Exp;
branches;
next	1.62;

1.62
date	99.07.01.08.28.47;	author rse;	state Exp;
branches;
next	1.61;

1.61
date	99.06.28.17.15.56;	author rse;	state Exp;
branches;
next	1.60;

1.60
date	99.06.28.17.12.19;	author rse;	state Exp;
branches;
next	1.59;

1.59
date	99.06.28.13.17.04;	author rse;	state Exp;
branches;
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1.58
date	99.06.28.11.36.26;	author rse;	state Exp;
branches;
next	1.57;

1.57
date	99.06.28.10.02.07;	author rse;	state Exp;
branches;
next	1.56;

1.56
date	99.06.28.09.45.24;	author rse;	state Exp;
branches;
next	1.55;

1.55
date	99.06.28.07.51.55;	author rse;	state Exp;
branches;
next	1.54;

1.54
date	99.06.27.15.40.30;	author rse;	state Exp;
branches;
next	1.53;

1.53
date	99.06.27.15.38.04;	author rse;	state Exp;
branches;
next	1.52;

1.52
date	99.06.26.12.58.14;	author rse;	state Exp;
branches;
next	1.51;

1.51
date	99.06.26.12.47.55;	author rse;	state Exp;
branches;
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1.50
date	99.06.25.15.28.13;	author rse;	state Exp;
branches;
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1.49
date	99.06.25.09.10.29;	author rse;	state Exp;
branches;
next	1.48;

1.48
date	99.06.24.12.24.46;	author rse;	state Exp;
branches;
next	1.47;

1.47
date	99.06.24.11.50.04;	author rse;	state Exp;
branches;
next	1.46;

1.46
date	99.06.24.10.54.29;	author rse;	state Exp;
branches;
next	1.45;

1.45
date	99.06.24.10.47.19;	author rse;	state Exp;
branches;
next	1.44;

1.44
date	99.06.21.15.47.19;	author rse;	state Exp;
branches;
next	1.43;

1.43
date	99.06.21.15.30.44;	author rse;	state Exp;
branches;
next	1.42;

1.42
date	99.06.21.15.24.04;	author rse;	state Exp;
branches;
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1.41
date	99.06.21.10.31.29;	author rse;	state Exp;
branches;
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1.40
date	99.06.21.10.11.44;	author rse;	state Exp;
branches;
next	1.39;

1.39
date	99.06.21.10.07.29;	author rse;	state Exp;
branches;
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1.38
date	99.06.21.08.32.07;	author rse;	state Exp;
branches;
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1.37
date	99.06.20.10.04.32;	author rse;	state Exp;
branches;
next	1.36;

1.36
date	99.06.20.09.52.02;	author rse;	state Exp;
branches;
next	1.35;

1.35
date	99.06.20.09.44.27;	author rse;	state Exp;
branches;
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1.34
date	99.06.19.11.47.14;	author rse;	state Exp;
branches;
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1.33
date	99.06.19.11.46.04;	author rse;	state Exp;
branches;
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1.32
date	99.06.09.06.51.19;	author rse;	state Exp;
branches;
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1.31
date	99.06.04.11.16.04;	author rse;	state Exp;
branches;
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1.30
date	99.06.04.11.14.36;	author rse;	state Exp;
branches;
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1.29
date	99.06.04.10.47.42;	author rse;	state Exp;
branches;
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1.28
date	99.06.03.09.31.47;	author rse;	state Exp;
branches;
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1.27
date	99.06.01.15.29.22;	author rse;	state Exp;
branches;
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1.26
date	99.06.01.09.55.26;	author rse;	state Exp;
branches;
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1.25
date	99.06.01.07.56.34;	author rse;	state Exp;
branches;
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1.24
date	99.05.30.09.33.47;	author rse;	state Exp;
branches;
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1.23
date	99.05.25.14.28.47;	author rse;	state Exp;
branches;
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1.22
date	99.05.25.14.24.16;	author rse;	state Exp;
branches;
next	1.21;

1.21
date	99.05.25.11.53.29;	author rse;	state Exp;
branches;
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1.20
date	99.05.24.15.50.20;	author rse;	state Exp;
branches;
next	1.19;

1.19
date	99.05.24.15.48.36;	author rse;	state Exp;
branches;
next	1.18;

1.18
date	99.05.24.15.21.30;	author rse;	state Exp;
branches;
next	1.17;

1.17
date	99.05.24.11.13.35;	author rse;	state Exp;
branches;
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@Adjusted all copyright messages for new year 2007.
@
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@##
##  GNU Pth - The GNU Portable Threads
##  Copyright (c) 1999-2007 Ralf S. Engelschall <rse@@engelschall.com>
##
##  This file is part of GNU Pth, a non-preemptive thread scheduling
##  library which can be found at http://www.gnu.org/software/pth/.
##
##  This library is free software; you can redistribute it and/or
##  modify it under the terms of the GNU Lesser General Public
##  License as published by the Free Software Foundation; either
##  version 2.1 of the License, or (at your option) any later version.
##
##  This library is distributed in the hope that it will be useful,
##  but WITHOUT ANY WARRANTY; without even the implied warranty of
##  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
##  Lesser General Public License for more details.
##
##  You should have received a copy of the GNU Lesser General Public
##  License along with this library; if not, write to the Free Software
##  Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307
##  USA, or contact Ralf S. Engelschall <rse@@engelschall.com>.
##
##  pth.pod: Pth manual page
##

#                            ``Real programmers don't document.
#                              Documentation is for wimps who can't
#                              read the listings of the object deck.''

=pod

=head1 NAME

B<pth> - GNU Portable Threads

=head1 VERSION

GNU Pth PTH_VERSION_STR

=head1 SYNOPSIS

=over 4

=item B<Global Library Management>

pth_init,
pth_kill,
pth_ctrl,
pth_version.

=item B<Thread Attribute Handling>

pth_attr_of,
pth_attr_new,
pth_attr_init,
pth_attr_set,
pth_attr_get,
pth_attr_destroy.

=item B<Thread Control>

pth_spawn,
pth_once,
pth_self,
pth_suspend,
pth_resume,
pth_yield,
pth_nap,
pth_wait,
pth_cancel,
pth_abort,
pth_raise,
pth_join,
pth_exit.

=item B<Utilities>

pth_fdmode,
pth_time,
pth_timeout,
pth_sfiodisc.

=item B<Cancellation Management>

pth_cancel_point,
pth_cancel_state.

=item B<Event Handling>

pth_event,
pth_event_typeof,
pth_event_extract,
pth_event_concat,
pth_event_isolate,
pth_event_walk,
pth_event_status,
pth_event_free.

=item B<Key-Based Storage>

pth_key_create,
pth_key_delete,
pth_key_setdata,
pth_key_getdata.

=item B<Message Port Communication>

pth_msgport_create,
pth_msgport_destroy,
pth_msgport_find,
pth_msgport_pending,
pth_msgport_put,
pth_msgport_get,
pth_msgport_reply.

=item B<Thread Cleanups>

pth_cleanup_push,
pth_cleanup_pop.

=item B<Process Forking>

pth_atfork_push,
pth_atfork_pop,
pth_fork.

=item B<Synchronization>

pth_mutex_init,
pth_mutex_acquire,
pth_mutex_release,
pth_rwlock_init,
pth_rwlock_acquire,
pth_rwlock_release,
pth_cond_init,
pth_cond_await,
pth_cond_notify,
pth_barrier_init,
pth_barrier_reach.

=item B<User-Space Context>

pth_uctx_create,
pth_uctx_make,
pth_uctx_switch,
pth_uctx_destroy.

=item B<Generalized POSIX Replacement API>

pth_sigwait_ev,
pth_accept_ev,
pth_connect_ev,
pth_select_ev,
pth_poll_ev,
pth_read_ev,
pth_readv_ev,
pth_write_ev,
pth_writev_ev,
pth_recv_ev,
pth_recvfrom_ev,
pth_send_ev,
pth_sendto_ev.

=item B<Standard POSIX Replacement API>

pth_nanosleep,
pth_usleep,
pth_sleep,
pth_waitpid,
pth_system,
pth_sigmask,
pth_sigwait,
pth_accept,
pth_connect,
pth_select,
pth_pselect,
pth_poll,
pth_read,
pth_readv,
pth_write,
pth_writev,
pth_pread,
pth_pwrite,
pth_recv,
pth_recvfrom,
pth_send,
pth_sendto.

=back

=head1 DESCRIPTION

  ____  _   _
 |  _ \| |_| |__
 | |_) | __| '_ \         ``Only those who attempt
 |  __/| |_| | | |          the absurd can achieve
 |_|    \__|_| |_|          the impossible.''

B<Pth> is a very portable POSIX/ANSI-C based library for Unix platforms which
provides non-preemptive priority-based scheduling for multiple threads of
execution (aka `multithreading') inside event-driven applications. All threads
run in the same address space of the application process, but each thread has
its own individual program counter, run-time stack, signal mask and C<errno>
variable.

The thread scheduling itself is done in a cooperative way, i.e., the threads
are managed and dispatched by a priority- and event-driven non-preemptive
scheduler. The intention is that this way both better portability and run-time
performance is achieved than with preemptive scheduling. The event facility
allows threads to wait until various types of internal and external events
occur, including pending I/O on file descriptors, asynchronous signals,
elapsed timers, pending I/O on message ports, thread and process termination,
and even results of customized callback functions.

B<Pth> also provides an optional emulation API for POSIX.1c threads
(`Pthreads') which can be used for backward compatibility to existing
multithreaded applications. See B<Pth>'s pthread(3) manual page for
details.

=head2 Threading Background

When programming event-driven applications, usually servers, lots of
regular jobs and one-shot requests have to be processed in parallel.
To efficiently simulate this parallel processing on uniprocessor
machines, we use `multitasking' -- that is, we have the application
ask the operating system to spawn multiple instances of itself. On
Unix, typically the kernel implements multitasking in a preemptive and
priority-based way through heavy-weight processes spawned with fork(2).
These processes usually do I<not> share a common address space. Instead
they are clearly separated from each other, and are created by direct
cloning a process address space (although modern kernels use memory
segment mapping and copy-on-write semantics to avoid unnecessary copying
of physical memory).

The drawbacks are obvious: Sharing data between the processes is
complicated, and can usually only be done efficiently through shared
memory (but which itself is not very portable). Synchronization is
complicated because of the preemptive nature of the Unix scheduler
(one has to use I<atomic> locks, etc). The machine's resources can be
exhausted very quickly when the server application has to serve too many
long-running requests (heavy-weight processes cost memory). And when
each request spawns a sub-process to handle it, the server performance
and responsiveness is horrible (heavy-weight processes cost time to
spawn). Finally, the server application doesn't scale very well with the
load because of these resource problems. In practice, lots of tricks
are usually used to overcome these problems - ranging from pre-forked
sub-process pools to semi-serialized processing, etc.

One of the most elegant ways to solve these resource- and data-sharing
problems is to have multiple I<light-weight> threads of execution
inside a single (heavy-weight) process, i.e., to use I<multithreading>.
Those I<threads> usually improve responsiveness and performance of the
application, often improve and simplify the internal program structure,
and most important, require less system resources than heavy-weight
processes. Threads are neither the optimal run-time facility for all
types of applications, nor can all applications benefit from them. But
at least event-driven server applications usually benefit greatly from
using threads.

=head2 The World of Threading

Even though lots of documents exists which describe and define the world
of threading, to understand B<Pth>, you need only basic knowledge about
threading. The following definitions of thread-related terms should at
least help you understand thread programming enough to allow you to use
B<Pth>.

=over 2

=item B<o> B<process> vs. B<thread>

A process on Unix systems consists of at least the following fundamental
ingredients: I<virtual memory table>, I<program code>, I<program
counter>, I<heap memory>, I<stack memory>, I<stack pointer>, I<file
descriptor set>, I<signal table>. On every process switch, the kernel
saves and restores these ingredients for the individual processes. On
the other hand, a thread consists of only a private program counter,
stack memory, stack pointer and signal table. All other ingredients, in
particular the virtual memory, it shares with the other threads of the
same process.

=item B<o> B<kernel-space> vs. B<user-space> threading

Threads on a Unix platform traditionally can be implemented either
inside kernel-space or user-space. When threads are implemented by the
kernel, the thread context switches are performed by the kernel without
the application's knowledge. Similarly, when threads are implemented in
user-space, the thread context switches are performed by an application
library, without the kernel's knowledge. There also are hybrid threading
approaches where, typically, a user-space library binds one or more
user-space threads to one or more kernel-space threads (there usually
called light-weight processes - or in short LWPs).

User-space threads are usually more portable and can perform faster
and cheaper context switches (for instance via swapcontext(2) or
setjmp(3)/longjmp(3)) than kernel based threads. On the other hand,
kernel-space threads can take advantage of multiprocessor machines and
don't have any inherent I/O blocking problems. Kernel-space threads are
usually scheduled in preemptive way side-by-side with the underlying
processes. User-space threads on the other hand use either preemptive or
non-preemptive scheduling.

=item B<o> B<preemptive> vs. B<non-preemptive> thread scheduling

In preemptive scheduling, the scheduler lets a thread execute until a
blocking situation occurs (usually a function call which would block)
or the assigned timeslice elapses. Then it detracts control from the
thread without a chance for the thread to object. This is usually
realized by interrupting the thread through a hardware interrupt
signal (for kernel-space threads) or a software interrupt signal (for
user-space threads), like C<SIGALRM> or C<SIGVTALRM>. In non-preemptive
scheduling, once a thread received control from the scheduler it keeps
it until either a blocking situation occurs (again a function call which
would block and instead switches back to the scheduler) or the thread
explicitly yields control back to the scheduler in a cooperative way.

=item B<o> B<concurrency> vs. B<parallelism>

Concurrency exists when at least two threads are I<in progress> at the
same time. Parallelism arises when at least two threads are I<executing>
simultaneously. Real parallelism can be only achieved on multiprocessor
machines, of course. But one also usually speaks of parallelism or
I<high concurrency> in the context of preemptive thread scheduling
and of I<low concurrency> in the context of non-preemptive thread
scheduling.

=item B<o> B<responsiveness>

The responsiveness of a system can be described by the user visible
delay until the system responses to an external request. When this delay
is small enough and the user doesn't recognize a noticeable delay,
the responsiveness of the system is considered good. When the user
recognizes or is even annoyed by the delay, the responsiveness of the
system is considered bad.

=item B<o> B<reentrant>, B<thread-safe> and B<asynchronous-safe> functions

A reentrant function is one that behaves correctly if it is called
simultaneously by several threads and then also executes simultaneously.
Functions that access global state, such as memory or files, of course,
need to be carefully designed in order to be reentrant. Two traditional
approaches to solve these problems are caller-supplied states and
thread-specific data.

Thread-safety is the avoidance of I<data races>, i.e., situations
in which data is set to either correct or incorrect value depending
upon the (unpredictable) order in which multiple threads access and
modify the data. So a function is thread-safe when it still behaves
semantically correct when called simultaneously by several threads (it
is not required that the functions also execute simultaneously). The
traditional approach to achieve thread-safety is to wrap a function body
with an internal mutual exclusion lock (aka `mutex'). As you should
recognize, reentrant is a stronger attribute than thread-safe, because
it is harder to achieve and results especially in no run-time contention
between threads. So, a reentrant function is always thread-safe, but not
vice versa.

Additionally there is a related attribute for functions named
asynchronous-safe, which comes into play in conjunction with signal
handlers. This is very related to the problem of reentrant functions. An
asynchronous-safe function is one that can be called safe and without
side-effects from within a signal handler context. Usually very few
functions are of this type, because an application is very restricted in
what it can perform from within a signal handler (especially what system
functions it is allowed to call). The reason mainly is, because only a
few system functions are officially declared by POSIX as guaranteed to
be asynchronous-safe. Asynchronous-safe functions usually have to be
already reentrant.

=back

=head2 User-Space Threads

User-space threads can be implemented in various way. The two
traditional approaches are:

=over 3

=item B<1.>

B<Matrix-based explicit dispatching between small units of execution:>

Here the global procedures of the application are split into small
execution units (each is required to not run for more than a few
milliseconds) and those units are implemented by separate functions.
Then a global matrix is defined which describes the execution (and
perhaps even dependency) order of these functions. The main server
procedure then just dispatches between these units by calling one
function after each other controlled by this matrix. The threads are
created by more than one jump-trail through this matrix and by switching
between these jump-trails controlled by corresponding occurred events.

This approach gives the best possible performance, because one can
fine-tune the threads of execution by adjusting the matrix, and the
scheduling is done explicitly by the application itself. It is also very
portable, because the matrix is just an ordinary data structure, and
functions are a standard feature of ANSI C.

The disadvantage of this approach is that it is complicated to write
large applications with this approach, because in those applications
one quickly gets hundreds(!) of execution units and the control flow
inside such an application is very hard to understand (because it is
interrupted by function borders and one always has to remember the
global dispatching matrix to follow it). Additionally, all threads
operate on the same execution stack. Although this saves memory, it is
often nasty, because one cannot switch between threads in the middle of
a function. Thus the scheduling borders are the function borders.

=item B<2.>

B<Context-based implicit scheduling between threads of execution:>

Here the idea is that one programs the application as with forked
processes, i.e., one spawns a thread of execution and this runs from the
begin to the end without an interrupted control flow. But the control
flow can be still interrupted - even in the middle of a function.
Actually in a preemptive way, similar to what the kernel does for the
heavy-weight processes, i.e., every few milliseconds the user-space
scheduler switches between the threads of execution. But the thread
itself doesn't recognize this and usually (except for synchronization
issues) doesn't have to care about this.

The advantage of this approach is that it's very easy to program,
because the control flow and context of a thread directly follows
a procedure without forced interrupts through function borders.
Additionally, the programming is very similar to a traditional and well
understood fork(2) based approach.

The disadvantage is that although the general performance is increased,
compared to using approaches based on heavy-weight processes, it is decreased
compared to the matrix-approach above. Because the implicit preemptive
scheduling does usually a lot more context switches (every user-space context
switch costs some overhead even when it is a lot cheaper than a kernel-level
context switch) than the explicit cooperative/non-preemptive scheduling.
Finally, there is no really portable POSIX/ANSI-C based way to implement
user-space preemptive threading. Either the platform already has threads,
or one has to hope that some semi-portable package exists for it. And
even those semi-portable packages usually have to deal with assembler
code and other nasty internals and are not easy to port to forthcoming
platforms.

=back

So, in short: the matrix-dispatching approach is portable and fast, but
nasty to program. The thread scheduling approach is easy to program,
but suffers from synchronization and portability problems caused by its
preemptive nature.

=head2 The Compromise of Pth

But why not combine the good aspects of both approaches while avoiding
their bad aspects? That's the goal of B<Pth>. B<Pth> implements
easy-to-program threads of execution, but avoids the problems of
preemptive scheduling by using non-preemptive scheduling instead.

This sounds like, and is, a useful approach. Nevertheless, one has to
keep the implications of non-preemptive thread scheduling in mind when
working with B<Pth>. The following list summarizes a few essential
points:

=over 2

=item B<o>

B<Pth provides maximum portability, but NOT the fanciest features>.

This is, because it uses a nifty and portable POSIX/ANSI-C approach for
thread creation (and this way doesn't require any platform dependent
assembler hacks) and schedules the threads in non-preemptive way (which
doesn't require unportable facilities like C<SIGVTALRM>). On the other
hand, this way not all fancy threading features can be implemented.
Nevertheless the available facilities are enough to provide a robust and
full-featured threading system.

=item B<o>

B<Pth increases the responsiveness and concurrency of an event-driven
application, but NOT the concurrency of number-crunching applications>.

The reason is the non-preemptive scheduling. Number-crunching
applications usually require preemptive scheduling to achieve
concurrency because of their long CPU bursts. For them, non-preemptive
scheduling (even together with explicit yielding) provides only the old
concept of `coroutines'. On the other hand, event driven applications
benefit greatly from non-preemptive scheduling. They have only short
CPU bursts and lots of events to wait on, and this way run faster under
non-preemptive scheduling because no unnecessary context switching
occurs, as it is the case for preemptive scheduling. That's why B<Pth>
is mainly intended for server type applications, although there is no
technical restriction.

=item B<o>

B<Pth requires thread-safe functions, but NOT reentrant functions>.

This nice fact exists again because of the nature of non-preemptive
scheduling, where a function isn't interrupted and this way cannot be
reentered before it returned. This is a great portability benefit,
because thread-safety can be achieved more easily than reentrance
possibility. Especially this means that under B<Pth> more existing
third-party libraries can be used without side-effects than it's the case
for other threading systems.

=item B<o>

B<Pth doesn't require any kernel support, but can NOT
benefit from multiprocessor machines>.

This means that B<Pth> runs on almost all Unix kernels, because the
kernel does not need to be aware of the B<Pth> threads (because they
are implemented entirely in user-space). On the other hand, it cannot
benefit from the existence of multiprocessors, because for this, kernel
support would be needed. In practice, this is no problem, because
multiprocessor systems are rare, and portability is almost more
important than highest concurrency.

=back

=head2 The life cycle of a thread

To understand the B<Pth> Application Programming Interface (API), it
helps to first understand the life cycle of a thread in the B<Pth>
threading system. It can be illustrated with the following directed
graph:

             NEW
              |
              V
      +---> READY ---+
      |       ^      |
      |       |      V
   WAITING <--+-- RUNNING
                     |
      :              V
   SUSPENDED       DEAD

When a new thread is created, it is moved into the B<NEW> queue of the
scheduler. On the next dispatching for this thread, the scheduler picks
it up from there and moves it to the B<READY> queue. This is a queue
containing all threads which want to perform a CPU burst. There they are
queued in priority order. On each dispatching step, the scheduler always
removes the thread with the highest priority only. It then increases the
priority of all remaining threads by 1, to prevent them from `starving'.

The thread which was removed from the B<READY> queue is the new
B<RUNNING> thread (there is always just one B<RUNNING> thread, of
course). The B<RUNNING> thread is assigned execution control. After
this thread yields execution (either explicitly by yielding execution
or implicitly by calling a function which would block) there are three
possibilities: Either it has terminated, then it is moved to the B<DEAD>
queue, or it has events on which it wants to wait, then it is moved into
the B<WAITING> queue. Else it is assumed it wants to perform more CPU
bursts and immediately enters the B<READY> queue again.

Before the next thread is taken out of the B<READY> queue, the
B<WAITING> queue is checked for pending events. If one or more events
occurred, the threads that are waiting on them are immediately moved to
the B<READY> queue.

The purpose of the B<NEW> queue has to do with the fact that in B<Pth>
a thread never directly switches to another thread. A thread always
yields execution to the scheduler and the scheduler dispatches to the
next thread. So a freshly spawned thread has to be kept somewhere until
the scheduler gets a chance to pick it up for scheduling. That is
what the B<NEW> queue is for.

The purpose of the B<DEAD> queue is to support thread joining. When a
thread is marked to be unjoinable, it is directly kicked out of the
system after it terminated. But when it is joinable, it enters the
B<DEAD> queue. There it remains until another thread joins it.

Finally, there is a special separated queue named B<SUSPENDED>, to where
threads can be manually moved from the B<NEW>, B<READY> or B<WAITING>
queues by the application. The purpose of this special queue is to
temporarily absorb suspended threads until they are again resumed by
the application. Suspended threads do not cost scheduling or event
handling resources, because they are temporarily completely out of the
scheduler's scope. If a thread is resumed, it is moved back to the queue
from where it originally came and this way again enters the schedulers
scope.

=head1 APPLICATION PROGRAMMING INTERFACE (API)

In the following the B<Pth> I<Application Programming Interface> (API)
is discussed in detail. With the knowledge given above, it should now
be easy to understand how to program threads with this API. In good
Unix tradition, B<Pth> functions use special return values (C<NULL>
in pointer context, C<FALSE> in boolean context and C<-1> in integer
context) to indicate an error condition and set (or pass through) the
C<errno> system variable to pass more details about the error to the
caller.

=head2 Global Library Management

The following functions act on the library as a whole.  They are used to
initialize and shutdown the scheduler and fetch information from it.

=over 4

=item int B<pth_init>(void);

This initializes the B<Pth> library. It has to be the first B<Pth> API
function call in an application, and is mandatory. It's usually done at
the begin of the main() function of the application. This implicitly
spawns the internal scheduler thread and transforms the single execution
unit of the current process into a thread (the `main' thread). It
returns C<TRUE> on success and C<FALSE> on error.

=item int B<pth_kill>(void);

This kills the B<Pth> library. It should be the last B<Pth> API function call
in an application, but is not really required. It's usually done at the end of
the main function of the application. At least, it has to be called from within
the main thread. It implicitly kills all threads and transforms back the
calling thread into the single execution unit of the underlying process.  The
usual way to terminate a B<Pth> application is either a simple
`C<pth_exit(0);>' in the main thread (which waits for all other threads to
terminate, kills the threading system and then terminates the process) or a
`C<pth_kill(); exit(0)>' (which immediately kills the threading system and
terminates the process). The pth_kill() return immediately with a return
code of C<FALSE> if it is not called from within the main thread. Else it
kills the threading system and returns C<TRUE>.

=item long B<pth_ctrl>(unsigned long I<query>, ...);

This is a generalized query/control function for the B<Pth> library.  The
argument I<query> is a bitmask formed out of one or more C<PTH_CTRL_>I<XXXX>
queries. Currently the following queries are supported:

=over 4

=item C<PTH_CTRL_GETTHREADS>

This returns the total number of threads currently in existence.  This query
actually is formed out of the combination of queries for threads in a
particular state, i.e., the C<PTH_CTRL_GETTHREADS> query is equal to the
OR-combination of all the following specialized queries:

C<PTH_CTRL_GETTHREADS_NEW> for the number of threads in the
new queue (threads created via pth_spawn(3) but still not
scheduled once), C<PTH_CTRL_GETTHREADS_READY> for the number of
threads in the ready queue (threads who want to do CPU bursts),
C<PTH_CTRL_GETTHREADS_RUNNING> for the number of running threads
(always just one thread!), C<PTH_CTRL_GETTHREADS_WAITING> for
the number of threads in the waiting queue (threads waiting for
events), C<PTH_CTRL_GETTHREADS_SUSPENDED> for the number of
threads in the suspended queue (threads waiting to be resumed) and
C<PTH_CTRL_GETTHREADS_DEAD> for the number of threads in the new queue
(terminated threads waiting for a join).

=item C<PTH_CTRL_GETAVLOAD>

This requires a second argument of type `C<float *>' (pointer to a floating
point variable).  It stores a floating point value describing the exponential
averaged load of the scheduler in this variable. The load is a function from
the number of threads in the ready queue of the schedulers dispatching unit.
So a load around 1.0 means there is only one ready thread (the standard
situation when the application has no high load). A higher load value means
there a more threads ready who want to do CPU bursts. The average load value
updates once per second only. The return value for this query is always 0.

=item C<PTH_CTRL_GETPRIO>

This requires a second argument of type `C<pth_t>' which identifies a
thread.  It returns the priority (ranging from C<PTH_PRIO_MIN> to
C<PTH_PRIO_MAX>) of the given thread.

=item C<PTH_CTRL_GETNAME>

This requires a second argument of type `C<pth_t>' which identifies a
thread. It returns the name of the given thread, i.e., the return value of
pth_ctrl(3) should be casted to a `C<char *>'.

=item C<PTH_CTRL_DUMPSTATE>

This requires a second argument of type `C<FILE *>' to which a summary
of the internal B<Pth> library state is written to. The main information
which is currently written out is the current state of the thread pool.

=item C<PTH_CTRL_FAVOURNEW>

This requires a second argument of type `C<int>' which specified whether
the B<GNU Pth> scheduler favours new threads on startup, i.e., whether
they are moved from the new queue to the top (argument is C<TRUE>) or
middle (argument is C<FALSE>) of the ready queue. The default is to
favour new threads to make sure they do not starve already at startup,
although this slightly violates the strict priority based scheduling.

=back

The function returns C<-1> on error.

=item long B<pth_version>(void);

This function returns a hex-value `0xI<V>I<RR>I<T>I<LL>' which describes the
current B<Pth> library version. I<V> is the version, I<RR> the revisions,
I<LL> the level and I<T> the type of the level (alphalevel=0, betalevel=1,
patchlevel=2, etc). For instance B<Pth> version 1.0b1 is encoded as 0x100101.
The reason for this unusual mapping is that this way the version number is
steadily I<increasing>. The same value is also available under compile time as
C<PTH_VERSION>.

=back

=head2 Thread Attribute Handling

Attribute objects are used in B<Pth> for two things: First stand-alone/unbound
attribute objects are used to store attributes for to be spawned threads.
Bounded attribute objects are used to modify attributes of already existing
threads. The following attribute fields exists in attribute objects:

=over 4

=item C<PTH_ATTR_PRIO> (read-write) [C<int>]

Thread Priority between C<PTH_PRIO_MIN> and C<PTH_PRIO_MAX>.
The default is C<PTH_PRIO_STD>.

=item C<PTH_ATTR_NAME> (read-write) [C<char *>]

Name of thread (up to 40 characters are stored only), mainly for debugging
purposes.

=item C<PTH_ATTR_DISPATCHES> (read-write) [C<int>]

In bounded attribute objects, this field is incremented every time the
context is switched to the associated thread.

=item C<PTH_ATTR_JOINABLE> (read-write> [C<int>]

The thread detachment type, C<TRUE> indicates a joinable thread,
C<FALSE> indicates a detached thread. When a thread is detached,
after termination it is immediately kicked out of the system instead of
inserted into the dead queue.

=item C<PTH_ATTR_CANCEL_STATE> (read-write) [C<unsigned int>]

The thread cancellation state, i.e., a combination of C<PTH_CANCEL_ENABLE> or
C<PTH_CANCEL_DISABLE> and C<PTH_CANCEL_DEFERRED> or
C<PTH_CANCEL_ASYNCHRONOUS>.

=item C<PTH_ATTR_STACK_SIZE> (read-write) [C<unsigned int>]

The thread stack size in bytes. Use lower values than 64 KB with great care!

=item C<PTH_ATTR_STACK_ADDR> (read-write) [C<char *>]

A pointer to the lower address of a chunk of malloc(3)'ed memory for the
stack.

=item C<PTH_ATTR_TIME_SPAWN> (read-only) [C<pth_time_t>]

The time when the thread was spawned.
This can be queried only when the attribute object is bound to a thread.

=item C<PTH_ATTR_TIME_LAST> (read-only) [C<pth_time_t>]

The time when the thread was last dispatched.
This can be queried only when the attribute object is bound to a thread.

=item C<PTH_ATTR_TIME_RAN> (read-only) [C<pth_time_t>]

The total time the thread was running.
This can be queried only when the attribute object is bound to a thread.

=item C<PTH_ATTR_START_FUNC> (read-only) [C<void *(*)(void *)>]

The thread start function.
This can be queried only when the attribute object is bound to a thread.

=item C<PTH_ATTR_START_ARG> (read-only) [C<void *>]

The thread start argument.
This can be queried only when the attribute object is bound to a thread.

=item C<PTH_ATTR_STATE> (read-only) [C<pth_state_t>]

The scheduling state of the thread, i.e., either C<PTH_STATE_NEW>,
C<PTH_STATE_READY>, C<PTH_STATE_WAITING>, or C<PTH_STATE_DEAD>
This can be queried only when the attribute object is bound to a thread.

=item C<PTH_ATTR_EVENTS> (read-only) [C<pth_event_t>]

The event ring the thread is waiting for.
This can be queried only when the attribute object is bound to a thread.

=item C<PTH_ATTR_BOUND> (read-only) [C<int>]

Whether the attribute object is bound (C<TRUE>) to a thread or not (C<FALSE>).

=back

The following API functions can be used to handle the attribute objects:

=over 4

=item pth_attr_t B<pth_attr_of>(pth_t I<tid>);

This returns a new attribute object I<bound> to thread I<tid>.  Any queries on
this object directly fetch attributes from I<tid>. And attribute modifications
directly change I<tid>. Use such attribute objects to modify existing threads.

=item pth_attr_t B<pth_attr_new>(void);

This returns a new I<unbound> attribute object. An implicit pth_attr_init() is
done on it. Any queries on this object just fetch stored attributes from it.
And attribute modifications just change the stored attributes.  Use such
attribute objects to pre-configure attributes for to be spawned threads.

=item int B<pth_attr_init>(pth_attr_t I<attr>);

This initializes an attribute object I<attr> to the default values:
C<PTH_ATTR_PRIO> := C<PTH_PRIO_STD>, C<PTH_ATTR_NAME> := `C<unknown>',
C<PTH_ATTR_DISPATCHES> := C<0>, C<PTH_ATTR_JOINABLE> := C<TRUE>,
C<PTH_ATTR_CANCELSTATE> := C<PTH_CANCEL_DEFAULT>,
C<PTH_ATTR_STACK_SIZE> := 64*1024 and
C<PTH_ATTR_STACK_ADDR> := C<NULL>. All other C<PTH_ATTR_*> attributes are
read-only attributes and don't receive default values in I<attr>, because they
exists only for bounded attribute objects.

=item int B<pth_attr_set>(pth_attr_t I<attr>, int I<field>, ...);

This sets the attribute field I<field> in I<attr> to a value
specified as an additional argument on the variable argument
list. The following attribute I<fields> and argument pairs can
be used:

 PTH_ATTR_PRIO           int
 PTH_ATTR_NAME           char *
 PTH_ATTR_DISPATCHES     int
 PTH_ATTR_JOINABLE       int
 PTH_ATTR_CANCEL_STATE   unsigned int
 PTH_ATTR_STACK_SIZE     unsigned int
 PTH_ATTR_STACK_ADDR     char *

=item int B<pth_attr_get>(pth_attr_t I<attr>, int I<field>, ...);

This retrieves the attribute field I<field> in I<attr> and stores its
value in the variable specified through a pointer in an additional
argument on the variable argument list. The following I<fields> and
argument pairs can be used:

 PTH_ATTR_PRIO           int *
 PTH_ATTR_NAME           char **
 PTH_ATTR_DISPATCHES     int *
 PTH_ATTR_JOINABLE       int *
 PTH_ATTR_CANCEL_STATE   unsigned int *
 PTH_ATTR_STACK_SIZE     unsigned int *
 PTH_ATTR_STACK_ADDR     char **
 PTH_ATTR_TIME_SPAWN     pth_time_t *
 PTH_ATTR_TIME_LAST      pth_time_t *
 PTH_ATTR_TIME_RAN       pth_time_t *
 PTH_ATTR_START_FUNC     void *(**)(void *)
 PTH_ATTR_START_ARG      void **
 PTH_ATTR_STATE          pth_state_t *
 PTH_ATTR_EVENTS         pth_event_t *
 PTH_ATTR_BOUND          int *

=item int B<pth_attr_destroy>(pth_attr_t I<attr>);

This destroys a attribute object I<attr>. After this I<attr> is no
longer a valid attribute object.

=back

=head2 Thread Control

The following functions control the threading itself and make up the main API
of the B<Pth> library.

=over 4

=item pth_t B<pth_spawn>(pth_attr_t I<attr>, void *(*I<entry>)(void *), void *I<arg>);

This spawns a new thread with the attributes given in I<attr> (or
C<PTH_ATTR_DEFAULT> for default attributes - which means that thread priority,
joinability and cancel state are inherited from the current thread) with the
starting point at routine I<entry>; the dispatch count is not inherited from
the current thread if I<attr> is not specified - rather, it is initialized
to zero.  This entry routine is called as `pth_exit(I<entry>(I<arg>))' inside
the new thread unit, i.e., I<entry>'s return value is fed to an implicit
pth_exit(3). So the thread can also exit by just returning. Nevertheless
the thread can also exit explicitly at any time by calling pth_exit(3). But
keep in mind that calling the POSIX function exit(3) still terminates the
complete process and not just the current thread.

There is no B<Pth>-internal limit on the number of threads one can spawn,
except the limit implied by the available virtual memory. B<Pth> internally
keeps track of thread in dynamic data structures. The function returns
C<NULL> on error.

=item int B<pth_once>(pth_once_t *I<ctrlvar>, void (*I<func>)(void *), void *I<arg>);

This is a convenience function which uses a control variable of type
C<pth_once_t> to make sure a constructor function I<func> is called only once
as `I<func>(I<arg>)' in the system. In other words: Only the first call to
pth_once(3) by any thread in the system succeeds. The variable referenced via
I<ctrlvar> should be declared as `C<pth_once_t> I<variable-name> =
C<PTH_ONCE_INIT>;' before calling this function.

=item pth_t B<pth_self>(void);

This just returns the unique thread handle of the currently running thread.
This handle itself has to be treated as an opaque entity by the application.
It's usually used as an argument to other functions who require an argument of
type C<pth_t>.

=item int B<pth_suspend>(pth_t I<tid>);

This suspends a thread I<tid> until it is manually resumed again via
pth_resume(3). For this, the thread is moved to the B<SUSPENDED> queue
and this way is completely out of the scheduler's event handling and
thread dispatching scope. Suspending the current thread is not allowed.
The function returns C<TRUE> on success and C<FALSE> on errors.

=item int B<pth_resume>(pth_t I<tid>);

This function resumes a previously suspended thread I<tid>, i.e. I<tid>
has to stay on the B<SUSPENDED> queue. The thread is moved to the
B<NEW>, B<READY> or B<WAITING> queue (dependent on what its state was
when the pth_suspend(3) call were made) and this way again enters the
event handling and thread dispatching scope of the scheduler. The
function returns C<TRUE> on success and C<FALSE> on errors.

=item int B<pth_raise>(pth_t I<tid>, int I<sig>)

This function raises a signal for delivery to thread I<tid> only.  When one
just raises a signal via raise(3) or kill(2), its delivered to an arbitrary
thread which has this signal not blocked.  With pth_raise(3) one can send a
signal to a thread and its guarantees that only this thread gets the signal
delivered. But keep in mind that nevertheless the signals I<action> is still
configured I<process>-wide.  When I<sig> is 0 plain thread checking is
performed, i.e., `C<pth_raise(tid, 0)>' returns C<TRUE> when thread I<tid>
still exists in the B<PTH> system but doesn't send any signal to it.

=item int B<pth_yield>(pth_t I<tid>);

This explicitly yields back the execution control to the scheduler thread.
Usually the execution is implicitly transferred back to the scheduler when a
thread waits for an event. But when a thread has to do larger CPU bursts, it
can be reasonable to interrupt it explicitly by doing a few pth_yield(3) calls
to give other threads a chance to execute, too.  This obviously is the
cooperating part of B<Pth>.  A thread I<has not> to yield execution, of
course. But when you want to program a server application with good response
times the threads should be cooperative, i.e., when they should split their CPU
bursts into smaller units with this call.

Usually one specifies I<tid> as C<NULL> to indicate to the scheduler that it
can freely decide which thread to dispatch next.  But if one wants to indicate
to the scheduler that a particular thread should be favored on the next
dispatching step, one can specify this thread explicitly. This allows the
usage of the old concept of I<coroutines> where a thread/routine switches to a
particular cooperating thread. If I<tid> is not C<NULL> and points to a I<new>
or I<ready> thread, it is guaranteed that this thread receives execution
control on the next dispatching step. If I<tid> is in a different state (that
is, not in C<PTH_STATE_NEW> or C<PTH_STATE_READY>) an error is reported.

The function usually returns C<TRUE> for success and only C<FALSE> (with
C<errno> set to C<EINVAL>) if I<tid> specified an invalid or still not
new or ready thread.

=item int B<pth_nap>(pth_time_t I<naptime>);

This functions suspends the execution of the current thread until I<naptime>
is elapsed. I<naptime> is of type C<pth_time_t> and this way has theoretically
a resolution of one microsecond. In practice you should neither rely on this
nor that the thread is awakened exactly after I<naptime> has elapsed. It's
only guarantees that the thread will sleep at least I<naptime>. But because
of the non-preemptive nature of B<Pth> it can last longer (when another thread
kept the CPU for a long time). Additionally the resolution is dependent of the
implementation of timers by the operating system and these usually have only a
resolution of 10 microseconds or larger. But usually this isn't important for
an application unless it tries to use this facility for real time tasks.

=item int B<pth_wait>(pth_event_t I<ev>);

This is the link between the scheduler and the event facility (see below for
the various pth_event_xxx() functions). It's modeled like select(2), i.e., one
gives this function one or more events (in the event ring specified by I<ev>)
on which the current thread wants to wait. The scheduler awakes the
thread when one ore more of them occurred or failed after tagging
them as such. The I<ev> argument is a I<pointer> to an event ring
which isn't changed except for the tagging. pth_wait(3) returns the
number of occurred or failed events and the application can use
pth_event_status(3) to test which events occurred or failed.

=item int B<pth_cancel>(pth_t I<tid>);

This cancels a thread I<tid>. How the cancellation is done depends on the
cancellation state of I<tid> which the thread can configure itself. When its
state is C<PTH_CANCEL_DISABLE> a cancellation request is just made pending.
When it is C<PTH_CANCEL_ENABLE> it depends on the cancellation type what is
performed. When its C<PTH_CANCEL_DEFERRED> again the cancellation request is
just made pending. But when its C<PTH_CANCEL_ASYNCHRONOUS> the thread is
immediately canceled before pth_cancel(3) returns. The effect of a thread
cancellation is equal to implicitly forcing the thread to call
`C<pth_exit(PTH_CANCELED)>' at one of his cancellation points.  In B<Pth>
thread enter a cancellation point either explicitly via pth_cancel_point(3) or
implicitly by waiting for an event.

=item int B<pth_abort>(pth_t I<tid>);

This is the cruel way to cancel a thread I<tid>. When it's already dead and
waits to be joined it just joins it (via `C<pth_join(>I<tid>C<, NULL)>') and
this way kicks it out of the system.  Else it forces the thread to be not
joinable and to allow asynchronous cancellation and then cancels it via
`C<pth_cancel(>I<tid>C<)>'.

=item int B<pth_join>(pth_t I<tid>, void **I<value>);

This joins the current thread with the thread specified via I<tid>.
It first suspends the current thread until the I<tid> thread has
terminated. Then it is awakened and stores the value of I<tid>'s
pth_exit(3) call into *I<value> (if I<value> and not C<NULL>) and
returns to the caller. A thread can be joined only when it has the
attribute C<PTH_ATTR_JOINABLE> set to C<TRUE> (the default). A thread
can only be joined once, i.e., after the pth_join(3) call the thread
I<tid> is completely removed from the system.

=item void B<pth_exit>(void *I<value>);

This terminates the current thread. Whether it's immediately removed
from the system or inserted into the dead queue of the scheduler depends
on its join type which was specified at spawning time. If it has the
attribute C<PTH_ATTR_JOINABLE> set to C<FALSE>, it's immediately removed
and I<value> is ignored. Else the thread is inserted into the dead queue
and I<value> remembered for a subsequent pth_join(3) call by another
thread.

=back

=head2 Utilities

Utility functions.

=over 4

=item int B<pth_fdmode>(int I<fd>, int I<mode>);

This switches the non-blocking mode flag on file descriptor I<fd>.  The
argument I<mode> can be C<PTH_FDMODE_BLOCK> for switching I<fd> into blocking
I/O mode, C<PTH_FDMODE_NONBLOCK> for switching I<fd> into non-blocking I/O
mode or C<PTH_FDMODE_POLL> for just polling the current mode. The current mode
is returned (either C<PTH_FDMODE_BLOCK> or C<PTH_FDMODE_NONBLOCK>) or
C<PTH_FDMODE_ERROR> on error. Keep in mind that since B<Pth> 1.1 there is no
longer a requirement to manually switch a file descriptor into non-blocking
mode in order to use it. This is automatically done temporarily inside B<Pth>.
Instead when you now switch a file descriptor explicitly into non-blocking
mode, pth_read(3) or pth_write(3) will never block the current thread.

=item pth_time_t B<pth_time>(long I<sec>, long I<usec>);

This is a constructor for a C<pth_time_t> structure which is a convenient
function to avoid temporary structure values. It returns a I<pth_time_t>
structure which holds the absolute time value specified by I<sec> and I<usec>.

=item pth_time_t B<pth_timeout>(long I<sec>, long I<usec>);

This is a constructor for a C<pth_time_t> structure which is a convenient
function to avoid temporary structure values.  It returns a I<pth_time_t>
structure which holds the absolute time value calculated by adding I<sec> and
I<usec> to the current time.

=item Sfdisc_t *B<pth_sfiodisc>(void);

This functions is always available, but only reasonably usable when B<Pth>
was built with B<Sfio> support (C<--with-sfio> option) and C<PTH_EXT_SFIO> is
then defined by C<pth.h>. It is useful for applications which want to use the
comprehensive B<Sfio> I/O library with the B<Pth> threading library. Then this
function can be used to get an B<Sfio> discipline structure (C<Sfdisc_t>)
which can be pushed onto B<Sfio> streams (C<Sfio_t>) in order to let this
stream use pth_read(3)/pth_write(2) instead of read(2)/write(2). The benefit
is that this way I/O on the B<Sfio> stream does only block the current thread
instead of the whole process. The application has to free(3) the C<Sfdisc_t>
structure when it is no longer needed. The Sfio package can be found at
http://www.research.att.com/sw/tools/sfio/.

=back

=head2 Cancellation Management

B<Pth> supports POSIX style thread cancellation via pth_cancel(3) and the
following two related functions:

=over 4

=item void B<pth_cancel_state>(int I<newstate>, int *I<oldstate>);

This manages the cancellation state of the current thread.  When I<oldstate>
is not C<NULL> the function stores the old cancellation state under the
variable pointed to by I<oldstate>. When I<newstate> is not C<0> it sets the
new cancellation state. I<oldstate> is created before I<newstate> is set.  A
state is a combination of C<PTH_CANCEL_ENABLE> or C<PTH_CANCEL_DISABLE> and
C<PTH_CANCEL_DEFERRED> or C<PTH_CANCEL_ASYNCHRONOUS>.
C<PTH_CANCEL_ENABLE|PTH_CANCEL_DEFERRED> (or C<PTH_CANCEL_DEFAULT>) is the
default state where cancellation is possible but only at cancellation points.
Use C<PTH_CANCEL_DISABLE> to complete disable cancellation for a thread and
C<PTH_CANCEL_ASYNCHRONOUS> for allowing asynchronous cancellations, i.e.,
cancellations which can happen at any time.

=item void B<pth_cancel_point>(void);

This explicitly enter a cancellation point. When the current cancellation
state is C<PTH_CANCEL_DISABLE> or no cancellation request is pending, this has
no side-effect and returns immediately. Else it calls
`C<pth_exit(PTH_CANCELED)>'.

=back

=head2 Event Handling

B<Pth> has a very flexible event facility which is linked into the scheduler
through the pth_wait(3) function. The following functions provide the handling
of event rings.

=over 4

=item pth_event_t B<pth_event>(unsigned long I<spec>, ...);

This creates a new event ring consisting of a single initial event.  The type
of the generated event is specified by I<spec>. The following types are
available:

=over 4

=item C<PTH_EVENT_FD>

This is a file descriptor event. One or more of C<PTH_UNTIL_FD_READABLE>,
C<PTH_UNTIL_FD_WRITEABLE> or C<PTH_UNTIL_FD_EXCEPTION> have to be OR-ed into
I<spec> to specify on which state of the file descriptor you want to wait.  The
file descriptor itself has to be given as an additional argument.  Example:
`C<pth_event(PTH_EVENT_FD|PTH_UNTIL_FD_READABLE, fd)>'.

=item C<PTH_EVENT_SELECT>

This is a multiple file descriptor event modeled directly after the select(2)
call (actually it is also used to implement pth_select(3) internally).  It's a
convenient way to wait for a large set of file descriptors at once and at each
file descriptor for a different type of state. Additionally as a nice
side-effect one receives the number of file descriptors which causes the event
to be occurred (using BSD semantics, i.e., when a file descriptor occurred in
two sets it's counted twice). The arguments correspond directly to the
select(2) function arguments except that there is no timeout argument (because
timeouts already can be handled via C<PTH_EVENT_TIME> events).

Example: `C<pth_event(PTH_EVENT_SELECT, &rc, nfd, rfds, wfds, efds)>' where
C<rc> has to be of type `C<int *>', C<nfd> has to be of type `C<int>' and
C<rfds>, C<wfds> and C<efds> have to be of type `C<fd_set *>' (see
select(2)). The number of occurred file descriptors are stored in C<rc>.

=item C<PTH_EVENT_SIGS>

This is a signal set event. The two additional arguments have to be a pointer
to a signal set (type `C<sigset_t *>') and a pointer to a signal number
variable (type `C<int *>').  This event waits until one of the signals in
the signal set occurred.  As a result the occurred signal number is stored in
the second additional argument. Keep in mind that the B<Pth> scheduler doesn't
block signals automatically.  So when you want to wait for a signal with this
event you've to block it via sigprocmask(2) or it will be delivered without
your notice. Example: `C<sigemptyset(&set); sigaddset(&set, SIGINT);
pth_event(PTH_EVENT_SIG, &set, &sig);>'.

=item C<PTH_EVENT_TIME>

This is a time point event. The additional argument has to be of type
C<pth_time_t> (usually on-the-fly generated via pth_time(3)). This events
waits until the specified time point has elapsed. Keep in mind that the value
is an absolute time point and not an offset. When you want to wait for a
specified amount of time, you've to add the current time to the offset
(usually on-the-fly achieved via pth_timeout(3)).  Example:
`C<pth_event(PTH_EVENT_TIME, pth_timeout(2,0))>'.

=item C<PTH_EVENT_MSG>

This is a message port event. The additional argument has to be of type
C<pth_msgport_t>. This events waits until one or more messages were received
on the specified message port.  Example: `C<pth_event(PTH_EVENT_MSG, mp)>'.

=item C<PTH_EVENT_TID>

This is a thread event. The additional argument has to be of type C<pth_t>.
One of C<PTH_UNTIL_TID_NEW>, C<PTH_UNTIL_TID_READY>, C<PTH_UNTIL_TID_WAITING>
or C<PTH_UNTIL_TID_DEAD> has to be OR-ed into I<spec> to specify on which
state of the thread you want to wait.  Example:
`C<pth_event(PTH_EVENT_TID|PTH_UNTIL_TID_DEAD, tid)>'.

=item C<PTH_EVENT_FUNC>

This is a custom callback function event. Three additional arguments
have to be given with the following types: `C<int (*)(void *)>',
`C<void *>' and `C<pth_time_t>'. The first is a function pointer to
a check function and the second argument is a user-supplied context
value which is passed to this function. The scheduler calls this
function on a regular basis (on his own scheduler stack, so be very
careful!) and the thread is kept sleeping while the function returns
C<FALSE>. Once it returned C<TRUE> the thread will be awakened. The
check interval is defined by the third argument, i.e., the check
function is polled again not until this amount of time elapsed. Example:
`C<pth_event(PTH_EVENT_FUNC, func, arg, pth_time(0,500000))>'.

=back

=item unsigned long B<pth_event_typeof>(pth_event_t I<ev>);

This returns the type of event I<ev>. It's a combination of the describing
C<PTH_EVENT_XX> and C<PTH_UNTIL_XX> value. This is especially useful to know
which arguments have to be supplied to the pth_event_extract(3) function.

=item int B<pth_event_extract>(pth_event_t I<ev>, ...);

When pth_event(3) is treated like sprintf(3), then this function is
sscanf(3), i.e., it is the inverse operation of pth_event(3). This means that
it can be used to extract the ingredients of an event.  The ingredients are
stored into variables which are given as pointers on the variable argument
list.  Which pointers have to be present depends on the event type and has to
be determined by the caller before via pth_event_typeof(3).

To make it clear, when you constructed I<ev> via `C<ev =
pth_event(PTH_EVENT_FD, fd);>' you have to extract it via
`C<pth_event_extract(ev, &fd)>', etc. For multiple arguments of an event the
order of the pointer arguments is the same as for pth_event(3). But always
keep in mind that you have to always supply I<pointers> to I<variables> and
these variables have to be of the same type as the argument of pth_event(3)
required.

=item pth_event_t B<pth_event_concat>(pth_event_t I<ev>, ...);

This concatenates one or more additional event rings to the event ring I<ev>
and returns I<ev>. The end of the argument list has to be marked with a
C<NULL> argument. Use this function to create real events rings out of the
single-event rings created by pth_event(3).

=item pth_event_t B<pth_event_isolate>(pth_event_t I<ev>);

This isolates the event I<ev> from possibly appended events in the event ring.
When in I<ev> only one event exists, this returns C<NULL>. When remaining
events exists, they form a new event ring which is returned.

=item pth_event_t B<pth_event_walk>(pth_event_t I<ev>, int I<direction>);

This walks to the next (when I<direction> is C<PTH_WALK_NEXT>) or previews
(when I<direction> is C<PTH_WALK_PREV>) event in the event ring I<ev> and
returns this new reached event. Additionally C<PTH_UNTIL_OCCURRED> can be
OR-ed into I<direction> to walk to the next/previous occurred event in the
ring I<ev>.

=item pth_status_t B<pth_event_status>(pth_event_t I<ev>);

This returns the status of event I<ev>. This is a fast operation
because only a tag on I<ev> is checked which was either set or still
not set by the scheduler. In other words: This doesn't check the
event itself, it just checks the last knowledge of the scheduler. The
possible returned status codes are: C<PTH_STATUS_PENDING> (event is
still pending), C<PTH_STATUS_OCCURRED> (event successfully occurred),
C<PTH_STATUS_FAILED> (event failed).

=item int B<pth_event_free>(pth_event_t I<ev>, int I<mode>);

This deallocates the event I<ev> (when I<mode> is C<PTH_FREE_THIS>) or all
events appended to the event ring under I<ev> (when I<mode> is
C<PTH_FREE_ALL>).

=back

=head2 Key-Based Storage

The following functions provide thread-local storage through unique keys
similar to the POSIX B<Pthread> API. Use this for thread specific global data.

=over 4

=item int B<pth_key_create>(pth_key_t *I<key>, void (*I<func>)(void *));

This created a new unique key and stores it in I<key>.  Additionally I<func>
can specify a destructor function which is called on the current threads
termination with the I<key>.

=item int B<pth_key_delete>(pth_key_t I<key>);

This explicitly destroys a key I<key>.

=item int B<pth_key_setdata>(pth_key_t I<key>, const void *I<value>);

This stores I<value> under I<key>.

=item void *B<pth_key_getdata>(pth_key_t I<key>);

This retrieves the value under I<key>.

=back

=head2 Message Port Communication

The following functions provide message ports which can be used for efficient
and flexible inter-thread communication.

=over 4

=item pth_msgport_t B<pth_msgport_create>(const char *I<name>);

This returns a pointer to a new message port. If name I<name>
is not C<NULL>, the I<name> can be used by other threads via
pth_msgport_find(3) to find the message port in case they do not know
directly the pointer to the message port.

=item void B<pth_msgport_destroy>(pth_msgport_t I<mp>);

This destroys a message port I<mp>. Before all pending messages on it are
replied to their origin message port.

=item pth_msgport_t B<pth_msgport_find>(const char *I<name>);

This finds a message port in the system by I<name> and returns the pointer to
it.

=item int B<pth_msgport_pending>(pth_msgport_t I<mp>);

This returns the number of pending messages on message port I<mp>.

=item int B<pth_msgport_put>(pth_msgport_t I<mp>, pth_message_t *I<m>);

This puts (or sends) a message I<m> to message port I<mp>.

=item pth_message_t *B<pth_msgport_get>(pth_msgport_t I<mp>);

This gets (or receives) the top message from message port I<mp>.  Incoming
messages are always kept in a queue, so there can be more pending messages, of
course.

=item int B<pth_msgport_reply>(pth_message_t *I<m>);

This replies a message I<m> to the message port of the sender.

=back

=head2 Thread Cleanups

Per-thread cleanup functions.

=over 4

=item int B<pth_cleanup_push>(void (*I<handler>)(void *), void *I<arg>);

This pushes the routine I<handler> onto the stack of cleanup routines for the
current thread.  These routines are called in LIFO order when the thread
terminates.

=item int B<pth_cleanup_pop>(int I<execute>);

This pops the top-most routine from the stack of cleanup routines for the
current thread. When I<execute> is C<TRUE> the routine is additionally called.

=back

=head2 Process Forking

The following functions provide some special support for process forking
situations inside the threading environment.

=over 4

=item int B<pth_atfork_push>(void (*I<prepare>)(void *), void (*)(void *I<parent>), void (*)(void *I<child>), void *I<arg>);

This function declares forking handlers to be called before and after
pth_fork(3), in the context of the thread that called pth_fork(3). The
I<prepare> handler is called before fork(2) processing commences. The
I<parent> handler is called   after fork(2) processing completes in the parent
process.  The I<child> handler is called after fork(2) processing completed in
the child process. If no handling is desired at one or more of these three
points, the corresponding handler can be given as C<NULL>.  Each handler is
called with I<arg> as the argument.

The order of calls to pth_atfork_push(3) is significant. The I<parent> and
I<child> handlers are called in the order in which they were established by
calls to pth_atfork_push(3), i.e., FIFO. The I<prepare> fork handlers are
called in the opposite order, i.e., LIFO.

=item int B<pth_atfork_pop>(void);

This removes the top-most handlers on the forking handler stack which were
established with the last pth_atfork_push(3) call. It returns C<FALSE> when no
more handlers couldn't be removed from the stack.

=item pid_t B<pth_fork>(void);

This is a variant of fork(2) with the difference that the current thread only
is forked into a separate process, i.e., in the parent process nothing changes
while in the child process all threads are gone except for the scheduler and
the calling thread. When you really want to duplicate all threads in the
current process you should use fork(2) directly. But this is usually not
reasonable. Additionally this function takes care of forking handlers as
established by pth_fork_push(3).

=back

=head2 Synchronization

The following functions provide synchronization support via mutual exclusion
locks (B<mutex>), read-write locks (B<rwlock>), condition variables (B<cond>)
and barriers (B<barrier>). Keep in mind that in a non-preemptive threading
system like B<Pth> this might sound unnecessary at the first look, because a
thread isn't interrupted by the system. Actually when you have a critical code
section which doesn't contain any pth_xxx() functions, you don't need any
mutex to protect it, of course.

But when your critical code section contains any pth_xxx() function the chance
is high that these temporarily switch to the scheduler. And this way other
threads can make progress and enter your critical code section, too.  This is
especially true for critical code sections which implicitly or explicitly use
the event mechanism.

=over 4

=item int B<pth_mutex_init>(pth_mutex_t *I<mutex>);

This dynamically initializes a mutex variable of type `C<pth_mutex_t>'.
Alternatively one can also use static initialization via `C<pth_mutex_t
mutex = PTH_MUTEX_INIT>'.

=item int B<pth_mutex_acquire>(pth_mutex_t *I<mutex>, int I<try>, pth_event_t I<ev>);

This acquires a mutex I<mutex>.  If the mutex is already locked by another
thread, the current threads execution is suspended until the mutex is unlocked
again or additionally the extra events in I<ev> occurred (when I<ev> is not
C<NULL>).  Recursive locking is explicitly supported, i.e., a thread is allowed
to acquire a mutex more than once before its released. But it then also has be
released the same number of times until the mutex is again lockable by others.
When I<try> is C<TRUE> this function never suspends execution. Instead it
returns C<FALSE> with C<errno> set to C<EBUSY>.

=item int B<pth_mutex_release>(pth_mutex_t *I<mutex>);

This decrements the recursion locking count on I<mutex> and when it is zero it
releases the mutex I<mutex>.

=item int B<pth_rwlock_init>(pth_rwlock_t *I<rwlock>);

This dynamically initializes a read-write lock variable of type
`C<pth_rwlock_t>'.  Alternatively one can also use static initialization
via `C<pth_rwlock_t rwlock = PTH_RWLOCK_INIT>'.

=item int B<pth_rwlock_acquire>(pth_rwlock_t *I<rwlock>, int I<op>, int I<try>, pth_event_t I<ev>);

This acquires a read-only (when I<op> is C<PTH_RWLOCK_RD>) or a read-write
(when I<op> is C<PTH_RWLOCK_RW>) lock I<rwlock>. When the lock is only locked
by other threads in read-only mode, the lock succeeds.  But when one thread
holds a read-write lock, all locking attempts suspend the current thread until
this lock is released again. Additionally in I<ev> events can be given to let
the locking timeout, etc. When I<try> is C<TRUE> this function never suspends
execution. Instead it returns C<FALSE> with C<errno> set to C<EBUSY>.

=item int B<pth_rwlock_release>(pth_rwlock_t *I<rwlock>);

This releases a previously acquired (read-only or read-write) lock.

=item int B<pth_cond_init>(pth_cond_t *I<cond>);

This dynamically initializes a condition variable variable of type
`C<pth_cond_t>'.  Alternatively one can also use static initialization via
`C<pth_cond_t cond = PTH_COND_INIT>'.

=item int B<pth_cond_await>(pth_cond_t *I<cond>, pth_mutex_t *I<mutex>, pth_event_t I<ev>);

This awaits a condition situation. The caller has to follow the semantics of
the POSIX condition variables: I<mutex> has to be acquired before this
function is called. The execution of the current thread is then suspended
either until the events in I<ev> occurred (when I<ev> is not C<NULL>) or
I<cond> was notified by another thread via pth_cond_notify(3).  While the
thread is waiting, I<mutex> is released. Before it returns I<mutex> is
reacquired.

=item int B<pth_cond_notify>(pth_cond_t *I<cond>, int I<broadcast>);

This notified one or all threads which are waiting on I<cond>.  When
I<broadcast> is C<TRUE> all thread are notified, else only a single
(unspecified) one.

=item int B<pth_barrier_init>(pth_barrier_t *I<barrier>, int I<threshold>);

This dynamically initializes a barrier variable of type `C<pth_barrier_t>'.
Alternatively one can also use static initialization via `C<pth_barrier_t
barrier = PTH_BARRIER_INIT(>I<threadhold>C<)>'.

=item int B<pth_barrier_reach>(pth_barrier_t *I<barrier>);

This function reaches a barrier I<barrier>. If this is the last thread (as
specified by I<threshold> on init of I<barrier>) all threads are awakened.
Else the current thread is suspended until the last thread reached the barrier
and this way awakes all threads. The function returns (beside C<FALSE> on
error) the value C<TRUE> for any thread which neither reached the barrier as
the first nor the last thread; C<PTH_BARRIER_HEADLIGHT> for the thread which
reached the barrier as the first thread and C<PTH_BARRIER_TAILLIGHT> for the
thread which reached the barrier as the last thread.

=back

=head2 User-Space Context

The following functions provide a stand-alone sub-API for user-space
context switching. It internally is based on the same underlying machine
context switching mechanism the threads in B<GNU Pth> are based on.
Hence these functions you can use for implementing your own simple
user-space threads. The C<pth_uctx_t> context is somewhat modeled after
POSIX ucontext(3).

The time required to create (via pth_uctx_make(3)) a user-space context
can range from just a few microseconds up to a more dramatical time
(depending on the machine context switching method which is available on
the platform). On the other hand, the raw performance in switching the
user-space contexts is always very good (nearly independent of the used
machine context switching method). For instance, on an Intel Pentium-III
CPU with 800Mhz running under FreeBSD 4 one usually achieves about
260,000 user-space context switches (via pth_uctx_switch(3)) per second.

=over 4

=item int B<pth_uctx_create>(pth_uctx_t *I<uctx>);

This function creates a user-space context and stores it into I<uctx>.
There is still no underlying user-space context configured. You still
have to do this with pth_uctx_make(3). On success, this function returns
C<TRUE>, else C<FALSE>.

=item int B<pth_uctx_make>(pth_uctx_t I<uctx>, char *I<sk_addr>, size_t I<sk_size>, const sigset_t *I<sigmask>, void (*I<start_func>)(void *), void *I<start_arg>, pth_uctx_t I<uctx_after>);

This function makes a new user-space context in I<uctx> which will
operate on the run-time stack I<sk_addr> (which is of maximum
size I<sk_size>), with the signals in I<sigmask> blocked (if
I<sigmask> is not C<NULL>) and starting to execute with the call
I<start_func>(I<start_arg>). If I<sk_addr> is C<NULL>, a stack
is dynamically allocated. The stack size I<sk_size> has to be at
least 16384 (16KB). If the start function I<start_func> returns and
I<uctx_after> is not C<NULL>, an implicit user-space context switch
to this context is performed. Else (if I<uctx_after> is C<NULL>) the
process is terminated with exit(3). This function is somewhat modeled
after POSIX makecontext(3). On success, this function returns C<TRUE>,
else C<FALSE>.

=item int B<pth_uctx_switch>(pth_uctx_t I<uctx_from>, pth_uctx_t I<uctx_to>);

This function saves the current user-space context in I<uctx_from> for
later restoring by another call to pth_uctx_switch(3) and restores
the new user-space context from I<uctx_to>, which previously had to
be set with either a previous call to pth_uctx_switch(3) or initially
by pth_uctx_make(3). This function is somewhat modeled after POSIX
swapcontext(3). If I<uctx_from> or I<uctx_to> are C<NULL> or if
I<uctx_to> contains no valid user-space context, C<FALSE> is returned
instead of C<TRUE>. These are the only errors possible.

=item int B<pth_uctx_destroy>(pth_uctx_t I<uctx>);

This function destroys the user-space context in I<uctx>. The run-time
stack associated with the user-space context is deallocated only if it
was not given by the application (see I<sk_addr> of pth_uctx_create(3)).
If I<uctx> is C<NULL>, C<FALSE> is returned instead of C<TRUE>. This is
the only error possible.

=back

=head2 Generalized POSIX Replacement API

The following functions are generalized replacements functions for the POSIX
API, i.e., they are similar to the functions under `B<Standard POSIX
Replacement API>' but all have an additional event argument which can be used
for timeouts, etc.

=over 4

=item int B<pth_sigwait_ev>(const sigset_t *I<set>, int *I<sig>, pth_event_t I<ev>);

This is equal to pth_sigwait(3) (see below), but has an additional event
argument I<ev>. When pth_sigwait(3) suspends the current threads execution it
usually only uses the signal event on I<set> to awake. With this function any
number of extra events can be used to awake the current thread (remember that
I<ev> actually is an event I<ring>).

=item int B<pth_connect_ev>(int I<s>, const struct sockaddr *I<addr>, socklen_t I<addrlen>, pth_event_t I<ev>);

This is equal to pth_connect(3) (see below), but has an additional event
argument I<ev>. When pth_connect(3) suspends the current threads execution it
usually only uses the I/O event on I<s> to awake. With this function any
number of extra events can be used to awake the current thread (remember that
I<ev> actually is an event I<ring>).

=item int B<pth_accept_ev>(int I<s>, struct sockaddr *I<addr>, socklen_t *I<addrlen>, pth_event_t I<ev>);

This is equal to pth_accept(3) (see below), but has an additional event
argument I<ev>. When pth_accept(3) suspends the current threads execution it
usually only uses the I/O event on I<s> to awake. With this function any
number of extra events can be used to awake the current thread (remember that
I<ev> actually is an event I<ring>).

=item int B<pth_select_ev>(int I<nfd>, fd_set *I<rfds>, fd_set *I<wfds>, fd_set *I<efds>, struct timeval *I<timeout>, pth_event_t I<ev>);

This is equal to pth_select(3) (see below), but has an additional event
argument I<ev>. When pth_select(3) suspends the current threads execution it
usually only uses the I/O event on I<rfds>, I<wfds> and I<efds> to awake. With
this function any number of extra events can be used to awake the current
thread (remember that I<ev> actually is an event I<ring>).

=item int B<pth_poll_ev>(struct pollfd *I<fds>, unsigned int I<nfd>, int I<timeout>, pth_event_t I<ev>);

This is equal to pth_poll(3) (see below), but has an additional event argument
I<ev>. When pth_poll(3) suspends the current threads execution it usually only
uses the I/O event on I<fds> to awake. With this function any number of extra
events can be used to awake the current thread (remember that I<ev> actually
is an event I<ring>).

=item ssize_t B<pth_read_ev>(int I<fd>, void *I<buf>, size_t I<nbytes>, pth_event_t I<ev>);

This is equal to pth_read(3) (see below), but has an additional event argument
I<ev>. When pth_read(3) suspends the current threads execution it usually only
uses the I/O event on I<fd> to awake. With this function any number of extra
events can be used to awake the current thread (remember that I<ev> actually
is an event I<ring>).

=item ssize_t B<pth_readv_ev>(int I<fd>, const struct iovec *I<iovec>, int I<iovcnt>, pth_event_t I<ev>);

This is equal to pth_readv(3) (see below), but has an additional event
argument I<ev>. When pth_readv(3) suspends the current threads execution it
usually only uses the I/O event on I<fd> to awake. With this function any
number of extra events can be used to awake the current thread (remember that
I<ev> actually is an event I<ring>).

=item ssize_t B<pth_write_ev>(int I<fd>, const void *I<buf>, size_t I<nbytes>, pth_event_t I<ev>);

This is equal to pth_write(3) (see below), but has an additional event argument
I<ev>. When pth_write(3) suspends the current threads execution it usually
only uses the I/O event on I<fd> to awake. With this function any number of
extra events can be used to awake the current thread (remember that I<ev>
actually is an event I<ring>).

=item ssize_t B<pth_writev_ev>(int I<fd>, const struct iovec *I<iovec>, int I<iovcnt>, pth_event_t I<ev>);

This is equal to pth_writev(3) (see below), but has an additional event
argument I<ev>. When pth_writev(3) suspends the current threads execution it
usually only uses the I/O event on I<fd> to awake. With this function any
number of extra events can be used to awake the current thread (remember that
I<ev> actually is an event I<ring>).

=item ssize_t B<pth_recv_ev>(int I<fd>, void *I<buf>, size_t I<nbytes>, int I<flags>, pth_event_t I<ev>);

This is equal to pth_recv(3) (see below), but has an additional event
argument I<ev>. When pth_recv(3) suspends the current threads execution it
usually only uses the I/O event on I<fd> to awake. With this function any
number of extra events can be used to awake the current thread (remember that
I<ev> actually is an event I<ring>).

=item ssize_t B<pth_recvfrom_ev>(int I<fd>, void *I<buf>, size_t I<nbytes>, int I<flags>, struct sockaddr *I<from>, socklen_t *I<fromlen>, pth_event_t I<ev>);

This is equal to pth_recvfrom(3) (see below), but has an additional event
argument I<ev>. When pth_recvfrom(3) suspends the current threads execution it
usually only uses the I/O event on I<fd> to awake. With this function any
number of extra events can be used to awake the current thread (remember that
I<ev> actually is an event I<ring>).

=item ssize_t B<pth_send_ev>(int I<fd>, const void *I<buf>, size_t I<nbytes>, int I<flags>, pth_event_t I<ev>);

This is equal to pth_send(3) (see below), but has an additional event
argument I<ev>. When pth_send(3) suspends the current threads execution it
usually only uses the I/O event on I<fd> to awake. With this function any
number of extra events can be used to awake the current thread (remember that
I<ev> actually is an event I<ring>).

=item ssize_t B<pth_sendto_ev>(int I<fd>, const void *I<buf>, size_t I<nbytes>, int I<flags>, const struct sockaddr *I<to>, socklen_t I<tolen>, pth_event_t I<ev>);

This is equal to pth_sendto(3) (see below), but has an additional event
argument I<ev>. When pth_sendto(3) suspends the current threads execution it
usually only uses the I/O event on I<fd> to awake. With this function any
number of extra events can be used to awake the current thread (remember that
I<ev> actually is an event I<ring>).

=back

=head2 Standard POSIX Replacement API

The following functions are standard replacements functions for the POSIX API.
The difference is mainly that they suspend the current thread only instead of
the whole process in case the file descriptors will block.

=over 4

=item int B<pth_nanosleep>(const struct timespec *I<rqtp>, struct timespec *I<rmtp>);

This is a variant of the POSIX nanosleep(3) function. It suspends the
current threads execution until the amount of time in I<rqtp> elapsed.
The thread is guaranteed to not wake up before this time, but because
of the non-preemptive scheduling nature of B<Pth>, it can be awakened
later, of course. If I<rmtp> is not C<NULL>, the C<timespec> structure
it references is updated to contain the unslept amount (the request time
minus the time actually slept time). The difference between nanosleep(3)
and pth_nanosleep(3) is that that pth_nanosleep(3) suspends only the
execution of the current thread and not the whole process.

=item int B<pth_usleep>(unsigned int I<usec>);

This is a variant of the 4.3BSD usleep(3) function. It suspends the current
threads execution until I<usec> microseconds (= I<usec>*1/1000000 sec)
elapsed.  The thread is guaranteed to not wake up before this time, but
because of the non-preemptive scheduling nature of B<Pth>, it can be awakened
later, of course.  The difference between usleep(3) and pth_usleep(3) is that
that pth_usleep(3) suspends only the execution of the current thread and not
the whole process.

=item unsigned int B<pth_sleep>(unsigned int I<sec>);

This is a variant of the POSIX sleep(3) function. It suspends the current
threads execution until I<sec> seconds elapsed.  The thread is guaranteed to
not wake up before this time, but because of the non-preemptive scheduling
nature of B<Pth>, it can be awakened later, of course.  The difference between
sleep(3) and pth_sleep(3) is that pth_sleep(3) suspends only the
execution of the current thread and not the whole process.

=item pid_t B<pth_waitpid>(pid_t I<pid>, int *I<status>, int I<options>);

This is a variant of the POSIX waitpid(2) function. It suspends the
current threads execution until I<status> information is available for a
terminated child process I<pid>.  The difference between waitpid(2) and
pth_waitpid(3) is that pth_waitpid(3) suspends only the execution of the
current thread and not the whole process.  For more details about the
arguments and return code semantics see waitpid(2).

=item int B<pth_system>(const char *I<cmd>);

This is a variant of the POSIX system(3) function. It executes the
shell command I<cmd> with Bourne Shell (C<sh>) and suspends the current
threads execution until this command terminates. The difference between
system(3) and pth_system(3) is that pth_system(3) suspends only
the execution of the current thread and not the whole process. For more
details about the arguments and return code semantics see system(3).

=item int B<pth_sigmask>(int I<how>, const sigset_t *I<set>, sigset_t *I<oset>)

This is the B<Pth> thread-related equivalent of POSIX sigprocmask(2) respectively
pthread_sigmask(3). The arguments I<how>, I<set> and I<oset> directly relate
to sigprocmask(2), because B<Pth> internally just uses sigprocmask(2) here. So
alternatively you can also directly call sigprocmask(2), but for consistency
reasons you should use this function pth_sigmask(3).

=item int B<pth_sigwait>(const sigset_t *I<set>, int *I<sig>);

This is a variant of the POSIX.1c sigwait(3) function. It suspends the current
threads execution until a signal in I<set> occurred and stores the signal
number in I<sig>. The important point is that the signal is not delivered to a
signal handler. Instead it's caught by the scheduler only in order to awake
the pth_sigwait() call. The trick and noticeable point here is that this way
you get an asynchronous aware application that is written completely
synchronously. When you think about the problem of I<asynchronous safe>
functions you should recognize that this is a great benefit.

=item int B<pth_connect>(int I<s>, const struct sockaddr *I<addr>, socklen_t I<addrlen>);

This is a variant of the 4.2BSD connect(2) function. It establishes a
connection on a socket I<s> to target specified in I<addr> and I<addrlen>.
The difference between connect(2) and pth_connect(3) is that
pth_connect(3) suspends only the execution of the current thread and not the
whole process.  For more details about the arguments and return code semantics
see connect(2).

=item int B<pth_accept>(int I<s>, struct sockaddr *I<addr>, socklen_t *I<addrlen>);

This is a variant of the 4.2BSD accept(2) function. It accepts a connection on
a socket by extracting the first connection request on the queue of pending
connections, creating a new socket with the same properties of I<s> and
allocates a new file descriptor for the socket (which is returned).  The
difference between accept(2) and pth_accept(3) is that pth_accept(3)
suspends only the execution of the current thread and not the whole process.
For more details about the arguments and return code semantics see accept(2).

=item int B<pth_select>(int I<nfd>, fd_set *I<rfds>, fd_set *I<wfds>, fd_set *I<efds>, struct timeval *I<timeout>);

This is a variant of the 4.2BSD select(2) function.  It examines the I/O
descriptor sets whose addresses are passed in I<rfds>, I<wfds>, and I<efds> to
see if some of their descriptors are ready for reading, are ready for writing,
or have an exceptional condition pending, respectively.  For more details
about the arguments and return code semantics see select(2).

=item int B<pth_pselect>(int I<nfd>, fd_set *I<rfds>, fd_set *I<wfds>, fd_set *I<efds>, const struct timespec *I<timeout>, const sigset_t *I<sigmask>);

This is a variant of the POSIX pselect(2) function, which in turn
is a stronger variant of 4.2BSD select(2). The difference is that
the higher-resolution C<struct timespec> is passed instead of the
lower-resolution C<struct timeval> and that a signal mask is specified
which is temporarily set while waiting for input. For more details about
the arguments and return code semantics see pselect(2) and select(2).

=item int B<pth_poll>(struct pollfd *I<fds>, unsigned int I<nfd>, int I<timeout>);

This is a variant of the SysV poll(2) function. It examines the I/O
descriptors which are passed in the array I<fds> to see if some of them are
ready for reading, are ready for writing, or have an exceptional condition
pending, respectively. For more details about the arguments and return code
semantics see poll(2).

=item ssize_t B<pth_read>(int I<fd>, void *I<buf>, size_t I<nbytes>);

This is a variant of the POSIX read(2) function. It reads up to I<nbytes>
bytes into I<buf> from file descriptor I<fd>.  The difference between read(2)
and pth_read(2) is that pth_read(2) suspends execution of the current
thread until the file descriptor is ready for reading. For more details about
the arguments and return code semantics see read(2).

=item ssize_t B<pth_readv>(int I<fd>, const struct iovec *I<iovec>, int I<iovcnt>);

This is a variant of the POSIX readv(2) function. It reads data from
file descriptor I<fd> into the first I<iovcnt> rows of the I<iov> vector.  The
difference between readv(2) and pth_readv(2) is that pth_readv(2)
suspends execution of the current thread until the file descriptor is ready for
reading. For more details about the arguments and return code semantics see
readv(2).

=item ssize_t B<pth_write>(int I<fd>, const void *I<buf>, size_t I<nbytes>);

This is a variant of the POSIX write(2) function. It writes I<nbytes> bytes
from I<buf> to file descriptor I<fd>.  The difference between write(2) and
pth_write(2) is that pth_write(2) suspends execution of the current
thread until the file descriptor is ready for writing.  For more details about
the arguments and return code semantics see write(2).

=item ssize_t B<pth_writev>(int I<fd>, const struct iovec *I<iovec>, int I<iovcnt>);

This is a variant of the POSIX writev(2) function. It writes data to
file descriptor I<fd> from the first I<iovcnt> rows of the I<iov> vector.  The
difference between writev(2) and pth_writev(2) is that pth_writev(2)
suspends execution of the current thread until the file descriptor is ready for
reading. For more details about the arguments and return code semantics see
writev(2).

=item ssize_t B<pth_pread>(int I<fd>, void *I<buf>, size_t I<nbytes>, off_t I<offset>);

This is a variant of the POSIX pread(3) function.  It performs the same action
as a regular read(2), except that it reads from a given position in the file
without changing the file pointer.  The first three arguments are the same as
for pth_read(3) with the addition of a fourth argument I<offset> for the
desired position inside the file.

=item ssize_t B<pth_pwrite>(int I<fd>, const void *I<buf>, size_t I<nbytes>, off_t I<offset>);

This is a variant of the POSIX pwrite(3) function.  It performs the same
action as a regular write(2), except that it writes to a given position in the
file without changing the file pointer. The first three arguments are the same
as for pth_write(3) with the addition of a fourth argument I<offset> for the
desired position inside the file.

=item ssize_t B<pth_recv>(int I<fd>, void *I<buf>, size_t I<nbytes>, int I<flags>);

This is a variant of the SUSv2 recv(2) function and equal to
``pth_recvfrom(fd, buf, nbytes, flags, NULL, 0)''.

=item ssize_t B<pth_recvfrom>(int I<fd>, void *I<buf>, size_t I<nbytes>, int I<flags>, struct sockaddr *I<from>, socklen_t *I<fromlen>);

This is a variant of the SUSv2 recvfrom(2) function. It reads up to
I<nbytes> bytes into I<buf> from file descriptor I<fd> while using
I<flags> and I<from>/I<fromlen>. The difference between recvfrom(2) and
pth_recvfrom(2) is that pth_recvfrom(2) suspends execution of the
current thread until the file descriptor is ready for reading. For more
details about the arguments and return code semantics see recvfrom(2).

=item ssize_t B<pth_send>(int I<fd>, const void *I<buf>, size_t I<nbytes>, int I<flags>);

This is a variant of the SUSv2 send(2) function and equal to
``pth_sendto(fd, buf, nbytes, flags, NULL, 0)''.

=item ssize_t B<pth_sendto>(int I<fd>, const void *I<buf>, size_t I<nbytes>, int I<flags>, const struct sockaddr *I<to>, socklen_t I<tolen>);

This is a variant of the SUSv2 sendto(2) function. It writes I<nbytes>
bytes from I<buf> to file descriptor I<fd> while using I<flags> and
I<to>/I<tolen>. The difference between sendto(2) and pth_sendto(2) is
that pth_sendto(2) suspends execution of the current thread until
the file descriptor is ready for writing. For more details about the
arguments and return code semantics see sendto(2).

=back

=head1 EXAMPLE

The following example is a useless server which does nothing more than
listening on TCP port 12345 and displaying the current time to the
socket when a connection was established. For each incoming connection a
thread is spawned. Additionally, to see more multithreading, a useless
ticker thread runs simultaneously which outputs the current time to
C<stderr> every 5 seconds. The example contains I<no> error checking and
is I<only> intended to show you the look and feel of B<Pth>.

 #include <stdio.h>
 #include <stdlib.h>
 #include <errno.h>
 #include <sys/types.h>
 #include <sys/socket.h>
 #include <netinet/in.h>
 #include <arpa/inet.h>
 #include <signal.h>
 #include <netdb.h>
 #include <unistd.h>
 #include "pth.h"

 #define PORT 12345

 /* the socket connection handler thread */
 static void *handler(void *_arg)
 {
     int fd = (int)_arg;
     time_t now;
     char *ct;

     now = time(NULL);
     ct = ctime(&now);
     pth_write(fd, ct, strlen(ct));
     close(fd);
     return NULL;
 }

 /* the stderr time ticker thread */
 static void *ticker(void *_arg)
 {
     time_t now;
     char *ct;
     float load;

     for (;;) {
         pth_sleep(5);
         now = time(NULL);
         ct = ctime(&now);
         ct[strlen(ct)-1] = '\0';
         pth_ctrl(PTH_CTRL_GETAVLOAD, &load);
         printf("ticker: time: %s, average load: %.2f\n", ct, load);
     }
 }

 /* the main thread/procedure */
 int main(int argc, char *argv[])
 {
     pth_attr_t attr;
     struct sockaddr_in sar;
     struct protoent *pe;
     struct sockaddr_in peer_addr;
     int peer_len;
     int sa, sw;
     int port;

     pth_init();
     signal(SIGPIPE, SIG_IGN);

     attr = pth_attr_new();
     pth_attr_set(attr, PTH_ATTR_NAME, "ticker");
     pth_attr_set(attr, PTH_ATTR_STACK_SIZE, 64*1024);
     pth_attr_set(attr, PTH_ATTR_JOINABLE, FALSE);
     pth_spawn(attr, ticker, NULL);

     pe = getprotobyname("tcp");
     sa = socket(AF_INET, SOCK_STREAM, pe->p_proto);
     sar.sin_family = AF_INET;
     sar.sin_addr.s_addr = INADDR_ANY;
     sar.sin_port = htons(PORT);
     bind(sa, (struct sockaddr *)&sar, sizeof(struct sockaddr_in));
     listen(sa, 10);

     pth_attr_set(attr, PTH_ATTR_NAME, "handler");
     for (;;) {
         peer_len = sizeof(peer_addr);
         sw = pth_accept(sa, (struct sockaddr *)&peer_addr, &peer_len);
         pth_spawn(attr, handler, (void *)sw);
     }
 }

=head1 BUILD ENVIRONMENTS

In this section we will discuss the canonical ways to establish the build
environment for a B<Pth> based program. The possibilities supported by B<Pth>
range from very simple environments to rather complex ones.

=head2 Manual Build Environment (Novice)

As a first example, assume we have the above test program staying in the
source file C<foo.c>. Then we can create a very simple build environment by
just adding the following C<Makefile>:

 $ vi Makefile
 | CC      = cc
 | CFLAGS  = `pth-config --cflags`
 | LDFLAGS = `pth-config --ldflags`
 | LIBS    = `pth-config --libs`
 |
 | all: foo
 | foo: foo.o
 |     $(CC) $(LDFLAGS) -o foo foo.o $(LIBS)
 | foo.o: foo.c
 |     $(CC) $(CFLAGS) -c foo.c
 | clean:
 |     rm -f foo foo.o

This imports the necessary compiler and linker flags on-the-fly from the
B<Pth> installation via its C<pth-config> program. This approach is
straight-forward and works fine for small projects.

=head2 Autoconf Build Environment (Advanced)

The previous approach is simple but inflexible. First, to speed up
building, it would be nice to not expand the compiler and linker flags
every time the compiler is started. Second, it would be useful to
also be able to build against uninstalled B<Pth>, that is, against
a B<Pth> source tree which was just configured and built, but not
installed. Third, it would be also useful to allow checking of the
B<Pth> version to make sure it is at least a minimum required version.
And finally, it would be also great to make sure B<Pth> works correctly
by first performing some sanity compile and run-time checks. All this
can be done if we use GNU B<autoconf> and the C<AC_CHECK_PTH> macro
provided by B<Pth>. For this, we establish the following three files:

First we again need the C<Makefile>, but this time it contains B<autoconf>
placeholders and additional cleanup targets. And we create it under the name
C<Makefile.in>, because it is now an input file for B<autoconf>:

 $ vi Makefile.in
 | CC      = @@CC@@
 | CFLAGS  = @@CFLAGS@@
 | LDFLAGS = @@LDFLAGS@@
 | LIBS    = @@LIBS@@
 |
 | all: foo
 | foo: foo.o
 |     $(CC) $(LDFLAGS) -o foo foo.o $(LIBS)
 | foo.o: foo.c
 |     $(CC) $(CFLAGS) -c foo.c
 | clean:
 |     rm -f foo foo.o
 | distclean:
 |     rm -f foo foo.o
 |     rm -f config.log config.status config.cache
 |     rm -f Makefile

Because B<autoconf> generates additional files, we added a canonical
C<distclean> target which cleans this up. Secondly, we wrote
C<configure.ac>, a (minimal) B<autoconf> script specification:

 $ vi configure.ac
 | AC_INIT(Makefile.in)
 | AC_CHECK_PTH(1.3.0)
 | AC_OUTPUT(Makefile)

Then we let B<autoconf>'s C<aclocal> program generate for us an C<aclocal.m4>
file containing B<Pth>'s C<AC_CHECK_PTH> macro. Then we generate the final
C<configure> script out of this C<aclocal.m4> file and the C<configure.ac>
file:

 $ aclocal --acdir=`pth-config --acdir`
 $ autoconf

After these steps, the working directory should look similar to this:

 $ ls -l
 -rw-r--r--  1 rse  users    176 Nov  3 11:11 Makefile.in
 -rw-r--r--  1 rse  users  15314 Nov  3 11:16 aclocal.m4
 -rwxr-xr-x  1 rse  users  52045 Nov  3 11:16 configure
 -rw-r--r--  1 rse  users     63 Nov  3 11:11 configure.ac
 -rw-r--r--  1 rse  users   4227 Nov  3 11:11 foo.c

If we now run C<configure> we get a correct C<Makefile> which
immediately can be used to build C<foo> (assuming that B<Pth> is already
installed somewhere, so that C<pth-config> is in C<$PATH>):

 $ ./configure
 creating cache ./config.cache
 checking for gcc... gcc
 checking whether the C compiler (gcc   ) works... yes
 checking whether the C compiler (gcc   ) is a cross-compiler... no
 checking whether we are using GNU C... yes
 checking whether gcc accepts -g... yes
 checking how to run the C preprocessor... gcc -E
 checking for GNU Pth... version 1.3.0, installed under /usr/local
 updating cache ./config.cache
 creating ./config.status
 creating Makefile
 rse@@en1:/e/gnu/pth/ac
 $ make
 gcc -g -O2 -I/usr/local/include -c foo.c
 gcc -L/usr/local/lib -o foo foo.o -lpth

If B<Pth> is installed in non-standard locations or C<pth-config>
is not in C<$PATH>, one just has to drop the C<configure> script
a note about the location by running C<configure> with the option
C<--with-pth=>I<dir> (where I<dir> is the argument which was used with
the C<--prefix> option when B<Pth> was installed).

=head2 Autoconf Build Environment with Local Copy of Pth (Expert)

Finally let us assume the C<foo> program stays under either a I<GPL> or
I<LGPL> distribution license and we want to make it a stand-alone package for
easier distribution and installation.  That is, we don't want to oblige the
end-user to install B<Pth> just to allow our C<foo> package to
compile. For this, it is a convenient practice to include the required
libraries (here B<Pth>) into the source tree of the package (here C<foo>).
B<Pth> ships with all necessary support to allow us to easily achieve this
approach. Say, we want B<Pth> in a subdirectory named C<pth/> and this
directory should be seamlessly integrated into the configuration and build
process of C<foo>.

First we again start with the C<Makefile.in>, but this time it is a more
advanced version which supports subdirectory movement:

 $ vi Makefile.in
 | CC      = @@CC@@
 | CFLAGS  = @@CFLAGS@@
 | LDFLAGS = @@LDFLAGS@@
 | LIBS    = @@LIBS@@
 |
 | SUBDIRS = pth
 |
 | all: subdirs_all foo
 |
 | subdirs_all:
 |     @@$(MAKE) $(MFLAGS) subdirs TARGET=all
 | subdirs_clean:
 |     @@$(MAKE) $(MFLAGS) subdirs TARGET=clean
 | subdirs_distclean:
 |     @@$(MAKE) $(MFLAGS) subdirs TARGET=distclean
 | subdirs:
 |     @@for subdir in $(SUBDIRS); do \
 |         echo "===> $$subdir ($(TARGET))"; \
 |         (cd $$subdir; $(MAKE) $(MFLAGS) $(TARGET) || exit 1) || exit 1; \
 |         echo "<=== $$subdir"; \
 |     done
 |
 | foo: foo.o
 |     $(CC) $(LDFLAGS) -o foo foo.o $(LIBS)
 | foo.o: foo.c
 |     $(CC) $(CFLAGS) -c foo.c
 |
 | clean: subdirs_clean
 |     rm -f foo foo.o
 | distclean: subdirs_distclean
 |     rm -f foo foo.o
 |     rm -f config.log config.status config.cache
 |     rm -f Makefile

Then we create a slightly different B<autoconf> script C<configure.ac>:

 $ vi configure.ac
 | AC_INIT(Makefile.in)
 | AC_CONFIG_AUX_DIR(pth)
 | AC_CHECK_PTH(1.3.0, subdir:pth --disable-tests)
 | AC_CONFIG_SUBDIRS(pth)
 | AC_OUTPUT(Makefile)

Here we provided a default value for C<foo>'s C<--with-pth> option as the
second argument to C<AC_CHECK_PTH> which indicates that B<Pth> can be found in
the subdirectory named C<pth/>. Additionally we specified that the
C<--disable-tests> option of B<Pth> should be passed to the C<pth/>
subdirectory, because we need only to build the B<Pth> library itself. And we
added a C<AC_CONFIG_SUBDIR> call which indicates to B<autoconf> that it should
configure the C<pth/> subdirectory, too. The C<AC_CONFIG_AUX_DIR> directive
was added just to make B<autoconf> happy, because it wants to find a
C<install.sh> or C<shtool> script if C<AC_CONFIG_SUBDIRS> is used.

Now we let B<autoconf>'s C<aclocal> program again generate for us an
C<aclocal.m4> file with the contents of B<Pth>'s C<AC_CHECK_PTH> macro.
Finally we generate the C<configure> script out of this C<aclocal.m4>
file and the C<configure.ac> file.

 $ aclocal --acdir=`pth-config --acdir`
 $ autoconf

Now we have to create the C<pth/> subdirectory itself. For this, we extract the
B<Pth> distribution to the C<foo> source tree and just rename it to C<pth/>:

 $ gunzip <pth-X.Y.Z.tar.gz | tar xvf -
 $ mv pth-X.Y.Z pth

Optionally to reduce the size of the C<pth/> subdirectory, we can strip down
the B<Pth> sources to a minimum with the I<striptease> feature:

 $ cd pth
 $ ./configure
 $ make striptease
 $ cd ..

After this the source tree of C<foo> should look similar to this:

 $ ls -l
 -rw-r--r--  1 rse  users    709 Nov  3 11:51 Makefile.in
 -rw-r--r--  1 rse  users  16431 Nov  3 12:20 aclocal.m4
 -rwxr-xr-x  1 rse  users  57403 Nov  3 12:21 configure
 -rw-r--r--  1 rse  users    129 Nov  3 12:21 configure.ac
 -rw-r--r--  1 rse  users   4227 Nov  3 11:11 foo.c
 drwxr-xr-x  2 rse  users   3584 Nov  3 12:36 pth
 $ ls -l pth/
 -rw-rw-r--  1 rse  users   26344 Nov  1 20:12 COPYING
 -rw-rw-r--  1 rse  users    2042 Nov  3 12:36 Makefile.in
 -rw-rw-r--  1 rse  users    3967 Nov  1 19:48 README
 -rw-rw-r--  1 rse  users     340 Nov  3 12:36 README.1st
 -rw-rw-r--  1 rse  users   28719 Oct 31 17:06 config.guess
 -rw-rw-r--  1 rse  users   24274 Aug 18 13:31 config.sub
 -rwxrwxr-x  1 rse  users  155141 Nov  3 12:36 configure
 -rw-rw-r--  1 rse  users  162021 Nov  3 12:36 pth.c
 -rw-rw-r--  1 rse  users   18687 Nov  2 15:19 pth.h.in
 -rw-rw-r--  1 rse  users    5251 Oct 31 12:46 pth_acdef.h.in
 -rw-rw-r--  1 rse  users    2120 Nov  1 11:27 pth_acmac.h.in
 -rw-rw-r--  1 rse  users    2323 Nov  1 11:27 pth_p.h.in
 -rw-rw-r--  1 rse  users     946 Nov  1 11:27 pth_vers.c
 -rw-rw-r--  1 rse  users   26848 Nov  1 11:27 pthread.c
 -rw-rw-r--  1 rse  users   18772 Nov  1 11:27 pthread.h.in
 -rwxrwxr-x  1 rse  users   26188 Nov  3 12:36 shtool

Now when we configure and build the C<foo> package it looks similar to this:

 $ ./configure
 creating cache ./config.cache
 checking for gcc... gcc
 checking whether the C compiler (gcc   ) works... yes
 checking whether the C compiler (gcc   ) is a cross-compiler... no
 checking whether we are using GNU C... yes
 checking whether gcc accepts -g... yes
 checking how to run the C preprocessor... gcc -E
 checking for GNU Pth... version 1.3.0, local under pth
 updating cache ./config.cache
 creating ./config.status
 creating Makefile
 configuring in pth
 running /bin/sh ./configure  --enable-subdir --enable-batch
 --disable-tests --cache-file=.././config.cache --srcdir=.
 loading cache .././config.cache
 checking for gcc... (cached) gcc
 checking whether the C compiler (gcc   ) works... yes
 checking whether the C compiler (gcc   ) is a cross-compiler... no
 [...]
 $ make
 ===> pth (all)
 ./shtool scpp -o pth_p.h -t pth_p.h.in -Dcpp -Cintern -M '==#==' pth.c
 pth_vers.c
 gcc -c -I. -O2 -pipe pth.c
 gcc -c -I. -O2 -pipe pth_vers.c
 ar rc libpth.a pth.o pth_vers.o
 ranlib libpth.a
 <=== pth
 gcc -g -O2 -Ipth -c foo.c
 gcc -Lpth -o foo foo.o -lpth

As you can see, B<autoconf> now automatically configures the local
(stripped down) copy of B<Pth> in the subdirectory C<pth/> and the
C<Makefile> automatically builds the subdirectory, too.

=head1 SYSTEM CALL WRAPPER FACILITY

B<Pth> per default uses an explicit API, including the system calls. For
instance you've to explicitly use pth_read(3) when you need a thread-aware
read(3) and cannot expect that by just calling read(3) only the current thread
is blocked. Instead with the standard read(3) call the whole process will be
blocked. But because for some applications (mainly those consisting of lots of
third-party stuff) this can be inconvenient.  Here it's required that a call
to read(3) `magically' means pth_read(3). The problem here is that such
magic B<Pth> cannot provide per default because it's not really portable.
Nevertheless B<Pth> provides a two step approach to solve this problem:

=head2 Soft System Call Mapping

This variant is available on all platforms and can I<always> be enabled by
building B<Pth> with C<--enable-syscall-soft>. This then triggers some
C<#define>'s in the C<pth.h> header which map for instance read(3) to
pth_read(3), etc. Currently the following functions are mapped: fork(2),
nanosleep(3), usleep(3), sleep(3), sigwait(3), waitpid(2), system(3),
select(2), poll(2), connect(2), accept(2), read(2), write(2), recv(2),
send(2), recvfrom(2), sendto(2).

The drawback of this approach is just that really all source files
of the application where these function calls occur have to include
C<pth.h>, of course. And this also means that existing libraries,
including the vendor's B<stdio>, usually will still block the whole
process if one of its I/O functions block.

=head2 Hard System Call Mapping

This variant is available only on those platforms where the syscall(2)
function exists and there it can be enabled by building B<Pth> with
C<--enable-syscall-hard>. This then builds wrapper functions (for instances
read(3)) into the B<Pth> library which internally call the real B<Pth>
replacement functions (pth_read(3)). Currently the following functions
are mapped: fork(2), nanosleep(3), usleep(3), sleep(3), waitpid(2),
system(3), select(2), poll(2), connect(2), accept(2), read(2), write(2).

The drawback of this approach is that it depends on syscall(2) interface
and prototype conflicts can occur while building the wrapper functions
due to different function signatures in the vendor C header files.
But the advantage of this mapping variant is that the source files of
the application where these function calls occur have not to include
C<pth.h> and that existing libraries, including the vendor's B<stdio>,
magically become thread-aware (and then block only the current thread).

=head1 IMPLEMENTATION NOTES

B<Pth> is very portable because it has only one part which perhaps has
to be ported to new platforms (the machine context initialization). But
it is written in a way which works on mostly all Unix platforms which
support makecontext(2) or at least sigstack(2) or sigaltstack(2) [see
C<pth_mctx.c> for details]. Any other B<Pth> code is POSIX and ANSI C
based only.

The context switching is done via either SUSv2 makecontext(2) or POSIX
make[sig]setjmp(3) and [sig]longjmp(3). Here all CPU registers, the
program counter and the stack pointer are switched. Additionally the
B<Pth> dispatcher switches also the global Unix C<errno> variable [see
C<pth_mctx.c> for details] and the signal mask (either implicitly via
sigsetjmp(3) or in an emulated way via explicit setprocmask(2) calls).

The B<Pth> event manager is mainly select(2) and gettimeofday(2) based,
i.e., the current time is fetched via gettimeofday(2) once per context
switch for time calculations and all I/O events are implemented via a
single central select(2) call [see C<pth_sched.c> for details].

The thread control block management is done via virtual priority
queues without any additional data structure overhead. For this, the
queue linkage attributes are part of the thread control blocks and the
queues are actually implemented as rings with a selected element as the
entry point [see C<pth_tcb.h> and C<pth_pqueue.c> for details].

Most time critical code sections (especially the dispatcher and event
manager) are speeded up by inline functions (implemented as ANSI C
pre-processor macros). Additionally any debugging code is I<completely>
removed from the source when not built with C<-DPTH_DEBUG> (see Autoconf
C<--enable-debug> option), i.e., not only stub functions remain [see
C<pth_debug.c> for details].

=head1 RESTRICTIONS

B<Pth> (intentionally) provides no replacements for non-thread-safe
functions (like strtok(3) which uses a static internal buffer) or
synchronous system functions (like gethostbyname(3) which doesn't
provide an asynchronous mode where it doesn't block). When you want to
use those functions in your server application together with threads,
you've to either link the application against special third-party
libraries (or for thread-safe/reentrant functions possibly against an
existing C<libc_r> of the platform vendor). For an asynchronous DNS
resolver library use the GNU B<adns> package from Ian Jackson ( see
http://www.gnu.org/software/adns/adns.html ).

=head1 HISTORY

The B<Pth> library was designed and implemented between February and
July 1999 by I<Ralf S. Engelschall> after evaluating numerous (mostly
preemptive) thread libraries and after intensive discussions with
I<Peter Simons>, I<Martin Kraemer>, I<Lars Eilebrecht> and I<Ralph
Babel> related to an experimental (matrix based) non-preemptive C++
scheduler class written by I<Peter Simons>.

B<Pth> was then implemented in order to combine the I<non-preemptive>
approach of multithreading (which provides better portability and
performance) with an API similar to the popular one found in B<Pthread>
libraries (which provides easy programming).

So the essential idea of the non-preemptive approach was taken over from
I<Peter Simons> scheduler. The priority based scheduling algorithm was
suggested by I<Martin Kraemer>. Some code inspiration also came from
an experimental threading library (B<rsthreads>) written by I<Robert
S. Thau> for an ancient internal test version of the Apache webserver.
The concept and API of message ports was borrowed from AmigaOS' B<Exec>
subsystem. The concept and idea for the flexible event mechanism came
from I<Paul Vixie>'s B<eventlib> (which can be found as a part of
B<BIND> v8).

=head1 BUG REPORTS AND SUPPORT

If you think you have found a bug in B<Pth>, you should send a report as
complete as possible to I<bug-pth@@gnu.org>. If you can, please try to
fix the problem and include a patch, made with 'C<diff -u3>', in your
report. Always, at least, include a reasonable amount of description in
your report to allow the author to deterministically reproduce the bug.

For further support you additionally can subscribe to the
I<pth-users@@gnu.org> mailing list by sending an Email to
I<pth-users-request@@gnu.org> with `C<subscribe pth-users>' (or
`C<subscribe pth-users> I<address>' if you want to subscribe
from a particular Email I<address>) in the body. Then you can
discuss your issues with other B<Pth> users by sending messages to
I<pth-users@@gnu.org>. Currently (as of August 2000) you can reach about
110 Pth users on this mailing list. Old postings you can find at
I<http://www.mail-archive.com/pth-users@@gnu.org/>.

=head1 SEE ALSO

=head2 Related Web Locations

`comp.programming.threads Newsgroup Archive',
http://www.deja.com/topics_if.xp?
search=topic&group=comp.programming.threads

`comp.programming.threads Frequently Asked Questions (F.A.Q.)',
http://www.lambdacs.com/newsgroup/FAQ.html

`I<Multithreading - Definitions and Guidelines>',
Numeric Quest Inc 1998;
http://www.numeric-quest.com/lang/multi-frame.html

`I<The Single UNIX Specification, Version 2 - Threads>',
The Open Group 1997;
http://www.opengroup.org/onlinepubs /007908799/xsh/threads.html

SMI Thread Resources,
Sun Microsystems Inc;
http://www.sun.com/workshop/threads/

Bibliography on threads and multithreading,
Torsten Amundsen;
http://liinwww.ira.uka.de/bibliography/Os/threads.html

=head2 Related Books

B. Nichols, D. Buttlar, J.P. Farrel:
`I<Pthreads Programming - A POSIX Standard for Better Multiprocessing>',
O'Reilly 1996;
ISBN 1-56592-115-1

B. Lewis, D. J. Berg:
`I<Multithreaded Programming with Pthreads>',
Sun Microsystems Press, Prentice Hall 1998;
ISBN 0-13-680729-1

B. Lewis, D. J. Berg:
`I<Threads Primer - A Guide To Multithreaded Programming>',
Prentice Hall 1996;
ISBN 0-13-443698-9

S. J. Norton, M. D. Dipasquale:
`I<Thread Time - The Multithreaded Programming Guide>',
Prentice Hall 1997;
ISBN 0-13-190067-6

D. R. Butenhof:
`I<Programming with POSIX Threads>',
Addison Wesley 1997;
ISBN 0-201-63392-2

=head2 Related Manpages

pth-config(1), pthread(3).

getcontext(2), setcontext(2), makecontext(2), swapcontext(2),
sigstack(2), sigaltstack(2), sigaction(2), sigemptyset(2), sigaddset(2),
sigprocmask(2), sigsuspend(2), sigsetjmp(3), siglongjmp(3), setjmp(3),
longjmp(3), select(2), gettimeofday(2).

=head1 AUTHOR

 Ralf S. Engelschall
 rse@@engelschall.com
 www.engelschall.com

=cut

@


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@
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##  Copyright (c) 1999-2006 Ralf S. Engelschall <rse@@engelschall.com>
@


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@Adjusted all copyright messages for new year 2005.
@
text
@d3 1
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##  Copyright (c) 1999-2005 Ralf S. Engelschall <rse@@engelschall.com>
@


1.165
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@The pth_uctx_save() and pth_uctx_restore() API functions
unfortunately were broken by design because they are C
_functions_. This leads to one more deadly nesting on the
run-time stack which effectively caused the pth_mctx_restore()
in pth_uctx_restore() to return to the end of pth_uctx_save()
but then the control flow unfortunately returns to the
pth_uctx_restore() caller instead of the pth_uctx_save() caller
because the call to pth_uctx_restore() had already overwritten the
run-time stack position where the original return address for the
pth_uctx_save() call was stored.

The only workaround would be to #define pth_uctx_save() and
pth_uctx_restore() as C _macros_, but this then would require that
lots of the GNU Pth internals from pth_mctx.c would have to be
exported in the GNU Pth API (which in turn is not acceptable). So,
the only consequence is to remove the two functions again from the
GNU Pth API.

Prompted by hints from: Stefan Brantschen <sbr@@acm.org>
@
text
@d3 1
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##  Copyright (c) 1999-2004 Ralf S. Engelschall <rse@@engelschall.com>
@


1.164
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@Added PTH_CTRL_FAVOURNEW control which allows the user
to disable the favouring of new threads on scheduling
to get more strict priority based scheduling behavior.

Triggered by: Vinu V <Vinu_V@@mindtree.com>
@
text
@a144 2
pth_uctx_save,
pth_uctx_restore,
d1521 2
a1522 2
have to do this with pth_uctx_make(3) or pth_uctx_set(3). On success,
this function returns C<TRUE>, else C<FALSE>.
a1538 17
=item int B<pth_uctx_save>(pth_uctx_t I<uctx>);

This function saves the current user-space context in I<uctx> for later
restoring by either pth_uctx_restore(3) or pth_uctx_switch(3). This
function is somewhat modeled after POSIX getcontext(3). If I<uctx> is
C<NULL>, C<FALSE> is returned instead of C<TRUE>. This is the only error
possible.

=item int B<pth_uctx_restore>(pth_uctx_t I<uctx>);

This function restores the current user-space context from I<uctx>,
which previously had to be set with either pth_uctx_make(3) or
pth_uctx_save(3). This function is somewhat modeled after POSIX
setcontext(3). If I<uctx> is C<NULL> or I<uctx> contains no valid
user-space context, C<FALSE> is returned instead of C<TRUE>. These are
the only errors possible.

d1542 7
a1548 7
later restoring by either pth_uctx_restore(3) or pth_uctx_switch(3) and
restores the new user-space context from I<uctx>, which previously
had to be set with either pth_uctx_make(3) or pth_uctx_save(3). This
function is somewhat modeled after POSIX swapcontext(3). If I<uctx_from>
or I<uctx_to> are C<NULL> or if I<uctx_to> contains no valid user-space
context, C<FALSE> is returned instead of C<TRUE>. These are the only
errors possible.
d1554 3
a1556 3
was given by the application (see I<sk_addr> of pth_uctx_create(3)).
If I<uctx> is C<NULL>, C<FALSE> is returned instead of C<TRUE>. This
is the only error possible.
@


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@
text
@d682 9
@


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@Adjusted all copyright messages for new year 2003.
@
text
@d3 1
a3 1
##  Copyright (c) 1999-2003 Ralf S. Engelschall <rse@@engelschall.com>
@


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@Added soft and hard syscall mapping for nanosleep(3) and
usleep(3) functions.
@
text
@d3 1
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##  Copyright (c) 1999-2002 Ralf S. Engelschall <rse@@engelschall.com>
@


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@1. The function "int pth_event_occurred(pth_event_t)" was replaced
with "pth_status_t pth_event_status(pth_event_t)" where pth_status_t
can have values of PTH_STATUS_PENDING (replacing the old FALSE return
value of pth_event_occurred), PTH_STATUS_OCCURRED (replacing
the old TRUE return value of pth_event_occurred), and
PTH_STATUS_FAILED (a new return value indicating an error in
processing the event). This was scheduler/event-manager errors can
be indicated which happended while processing the event. For
backward compatibility reasons, a macro pth_event_occurred() was
added. This will be removed soon.

2. Use the new PTH_STATUS_FAILED event status in the scheduler's
event-manager for filedescriptor events if the internal select(2)
call returned with an error. Additionally this PTH_STATUS_FAILED
is recognized by the high-level API functions (pth_select, etc)
and produce the necessary POSIX conforming return codes (usually
-1 and errno == EBADF).

Parts submitted by: Thanh Luu <tluu@@synapcity.com>
@
text
@d2270 3
a2272 3
sleep(3), sigwait(3), waitpid(2), system(3), select(2), poll(2),
connect(2), accept(2), read(2), write(2), recv(2), send(2), recvfrom(2),
sendto(2).
d2287 2
a2288 2
are mapped: fork(2), sleep(3), waitpid(2), system(3), select(2),
poll(2), connect(2), accept(2), read(2), write(2).
@


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log
@Added thread attribute PTH_ATTR_DISPATCHES which (in bounded
attribute objects) is incremented every time the context
is switched to the associated thread. This can be used for
statistical information.
@
text
@d96 1
a96 1
pth_event_occurred,
d973 6
a978 5
on which the current thread wants to wait.  The scheduler awakes the thread
when one ore more of them occurred after tagging them as occurred. The I<ev>
argument is a I<pointer> to an event ring which isn't changed except for the
tagging. pth_wait(3) returns the number of occurred events and the application
can use pth_event_occurred(3) to test which events occurred.
d1240 1
a1240 1
=item int B<pth_event_occurred>(pth_event_t I<ev>);
d1242 7
a1248 4
This checks whether the event I<ev> occurred. This is a fast operation because
only a tag on I<ev> is checked which was either set or still not set by the
scheduler. In other words: This doesn't check the event itself, it just checks
the last knowledge of the scheduler.
@


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log
@Added a stand-alone sub-API for manual user-space context switching.
It is somewhat modeled after the POSIX ucontext(3) facility and
consists of an opaque data type pth_uctx_t and the management functions
pth_uctx_create(), pth_uctx_make(), pth_uctx_save(), pth_uctx_restore(),
pth_uctx_switch() and pth_uctx_destroy(). These functions are based on
the same underlying machine context switching facility (pth_mctx) the
threads in GNU Pth are using. This facility can be used to implement
co-routines without a full real multithreading environment or even to
implement an own multithreading environment.
@
text
@d717 5
d807 3
a809 2
C<PTH_ATTR_JOINABLE> := C<TRUE>, C<PTH_ATTR_CANCELSTATE> :=
C<PTH_CANCEL_DEFAULT>, C<PTH_ATTR_STACK_SIZE> := 64*1024 and
d823 1
d838 1
d871 8
a878 6
starting point at routine I<entry>. This entry routine is called as
`pth_exit(I<entry>(I<arg>))' inside the new thread unit, i.e., I<entry>'s
return value is fed to an implicit pth_exit(3). So the thread usually can exit
by just returning. Nevertheless the thread can also exit explicitly at any
time by calling pth_exit(3). But keep in mind that calling the POSIX function
exit(3) still terminates the complete process and not just the current thread.
@


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@Add a Pth variant of the new POSIX pselect(2) function, including
soft and hard syscall mapping support for it.
@
text
@d141 9
d1473 80
@


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@Added pth_nanosleep() function.

Obtained from: NetBSD, Nick Hudson <skrll@@netbsd.org>
@
text
@d169 1
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@


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log
@Matthew Mondor <mmondor@@gobot.ca> wrote:

> I noticed that pth_msgport_create(), although inspired from the AmigaOS
> API, does not support NULL for port identifyer, which would be very
> useful for thread-specific private message ports (mmftpd uses those and
> unfortunately currently has to generate unique strings to create ports).
> AmigaOS had this functionality...

So, make him happy and allow NULL from now on, too.
@
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@remove trailing whitespaces
@
text
@d1269 4
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This returns a pointer to a new message port with name I<name>. The I<name>
can be used by other threads via pth_msgport_find(3) to find the message port
in case they do not know directly the pointer to the message port.
@


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@Fixed more ENglish errors.

Submitted by: Felix Berger <bflat1@@gmx.net>
@
text
@d555 2
a556 2
the scheduler gets a chance to pick it up for scheduling. That is 
what the B<NEW> queue is for. 
d802 1
a802 1
be used: 
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a808 1
 PTH_ATTR_STACK_SIZE     unsigned int 
d1647 1
a1647 1
The difference between connect(2) and pth_connect(3) is that 
@


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@Woohhooo! Major GNU Pth source tree overhauling:
- Removed all generated files from CVS.
- Use OSSP devtool stuff to re-generate files on demand.
- Switched to Autoconf 2.52 and Libtool 1.4.2 environment.
@
text
@d492 1
a492 1
third-party libraries can be used without side-effects than its the case
d555 1
a555 1
the scheduler gets a chance to pick it up for scheduling. That is for
d576 2
a577 2
is discussed in detail. With the knowledge given above, it should be
now easy to understand how to program threads with this API. In good
d612 1
a612 1
code of C<FALSE> if it is called not from within the main thread. Else
d770 1
a770 1
The following API functions exists to handle the attribute objects:
d842 2
a843 2
The following functions control the threading itself and form the main API of
the B<Pth> library.
d931 1
a931 1
C<errno> set to C<EINVAL>) if I<tid> specified and invalid or still not
d1005 1
a1005 1
The following functions are utility functions.
d1305 1
a1305 1
The following functions provide per-thread cleanup functions.
d1591 1
a1591 1
elapsed.  The thread is guaranteed to not awakened before this time, but
d1601 1
a1601 1
not awakened before this time, but because of the non-preemptive scheduling
d1603 1
a1603 1
sleep(3) and pth_sleep(3) is that that pth_sleep(3) suspends only the
d1611 1
a1611 1
pth_waitpid(3) is that that pth_waitpid(3) suspends only the execution of the
d1620 1
a1620 1
system(3) and pth_system(3) is that that pth_system(3) suspends only
d1647 1
a1647 1
The difference between connect(2) and pth_connect(3) is that that
d1658 1
a1658 1
difference between accept(2) and pth_accept(3) is that that pth_accept(3)
d1682 1
a1682 1
and pth_read(2) is that that pth_read(2) suspends execution of the current
d1690 1
a1690 1
difference between readv(2) and pth_readv(2) is that that pth_readv(2)
d1699 1
a1699 1
pth_write(2) is that that pth_write(2) suspends execution of the current
d1707 1
a1707 1
difference between writev(2) and pth_writev(2) is that that pth_writev(2)
d1738 1
a1738 1
pth_recvfrom(2) is that that pth_recvfrom(2) suspends execution of the
d1752 1
a1752 1
that that pth_sendto(2) suspends execution of the current thread until
d1881 1
a1881 1
The previous approach is simple but unflexible. First, to speed up
d1884 1
a1884 1
also be able to build against an uninstalled B<Pth>, that is, against
d2199 1
a2199 1
manager) are speeded up by inlined functions (implemented as ANSI C
@


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@bump copyright year
@
text
@d1917 1
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C<configure.in>, a (minimal) B<autoconf> script specification:
d1919 1
a1919 1
 $ vi configure.in
d1926 1
a1926 1
C<configure> script out of this C<aclocal.m4> file and the C<configure.in>
d1938 1
a1938 1
 -rw-r--r--  1 rse  users     63 Nov  3 11:11 configure.in
d2019 1
a2019 1
Then we create a slightly different B<autoconf> script C<configure.in>:
d2021 1
a2021 1
 $ vi configure.in
d2041 1
a2041 1
file and the C<configure.in> file.
d2066 1
a2066 1
 -rw-r--r--  1 rse  users    129 Nov  3 12:21 configure.in
@


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@fix typo (found by Takashi Ishihara <tishihara@@ucdavis.edu>)
@
text
@d3 1
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##  Copyright (c) 1999-2001 Ralf S. Engelschall <rse@@engelschall.com>
@


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@
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@d1100 1
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C<PTH_UNTIL_FD_WRITEABLE> or C<PTH_UNTIL_FD_EXECPTION> have to be OR-ed into
@


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@
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@d1916 2
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C<distclean> target which cleanups this, too. Second, we write
a (minimalistic) B<autoconf> script specification in a file
C<configure.in>:
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easier distribution and installation.  That is, we don't want that the
end-user first has to install B<Pth> just to allow our C<foo> package to
@


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@*** empty log message ***
@
text
@d708 4
a711 3
The thread detachment type, C<TRUE> indicates a joinable thread, C<FALSE>
indicates a detached thread.  When a the is detached after termination it is
immediately kicked out of the system instead of inserted into the dead queue.
d982 8
a989 7
This joins the current thread with the thread specified via I<tid>.  It first
suspends the current thread until the I<tid> thread has terminated. Then it is
awakened and stores the value of I<tid>'s pth_exit(3) call into *I<value> (if
I<value> and not C<NULL>) and returns to the caller.  A thread can be joined
only when it was I<not> spawned with C<PTH_FLAG_NOJOIN>. A thread can only be
joined once, i.e., after the pth_join(3) call the thread I<tid> is removed
from the system.
d993 7
a999 6
This terminates the current thread. Whether it's immediately removed from the
system or inserted into the dead queue of the scheduler depends on its join
type which was specified at spawning time. When it was spawned with
C<PTH_FLAG_NOJOIN> it's immediately removed and I<value> is ignored.
Else the thread is inserted into the dead queue and I<value> remembered
for a pth_join(3) call by another thread.
@


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@
text
@d2201 1
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C<pth_debug.h> for details].
@


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@
text
@d1442 1
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=item int B<pth_barrier_init>(pth_barrier_t *I<barrier>, int I<threshold);
@


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@
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##  Copyright (c) 1999-2000 Ralf S. Engelschall <rse@@engelschall.com>
@


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@
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@d2140 1
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pth_read(3), etc.  Currently the following functions are mapped: fork(2),
d2142 2
a2143 1
connect(2), accept(2), read(2), write(2).
@


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@
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@d162 1
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sleep(3), sigwait(3), waitpid(2), select(2), poll(2), connect(2),
accept(2), read(2), write(2).
d2156 3
a2158 3
replacement functions (pth_read(3)).  Currently the following functions are
mapped: fork(2), sleep(3), waitpid(2), select(2), poll(2), connect(2),
accept(2), read(2), write(2).
@


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@
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usually only uses the I/O event on I<fd> to awake. With this function any
d1489 1
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usually only uses the I/O event on I<fd> to awake. With this function any
@


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@
text
@d1587 1
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elapsed. The thread is guaranteed to not awakened before this time, but
d1589 1
a1589 1
later, of course. The difference between usleep(3) and pth_usleep(3) is that
d1591 1
a1591 3
the whole process.  The function returns the value C<0> if successful,
otherwise the value C<-1> is returned and the global variable C<errno> is set
to indicate the error.
d1595 6
a1600 10
This is a variant of the POSIX sleep(3) function. It
suspends the current threads execution until I<sec> seconds elapsed.  The
thread is guaranteed to not awakened before this time, but because of the
non-preemptive scheduling nature of B<Pth>, it can be awakened later, of
course. The difference between sleep(3) and pth_sleep(3) is that that
pth_sleep(3) suspends only the execution of the current thread and not the
whole process.  If the function returns because the requested time has
elapsed, the value returned will be C<0>. If the function returns due to the
delivery of a signal, the value returned will be the unslept amount (the
requested time minus the time actually slept) in seconds.
@


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@
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@d1586 2
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threads execution until I<usec> microsecond (= I<usec> * 1/1000000 sec)
elapsed.  The thread is guaranteed to not awakened before this time, but
d1589 1
a1589 1
later, of course.  The difference between usleep(3) and pth_usleep(3) is that
d1591 3
a1593 1
the whole process.
d1601 1
a1601 1
course.  The difference between sleep(3) and pth_sleep(3) is that that
d1603 4
a1606 1
whole process.
@


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@*** empty log message ***
@
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@d2244 3
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I<pth-users@@gnu.org>. Currently (as of January 2000) you can reach about
50 Pth users on this mailing list.
@


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@
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@d293 1
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=item B<o> B<preemtive> vs. B<non-preemtive> thread scheduling
d538 1
a538 1
this thread yields execution (either explicitly by yielding excution
d1163 1
a1163 1
C<FALSE>. Once it returned C<TRUE> the thread will be awakend. The
d1865 1
a1865 1
straight-foreward and works fine for small projects.
d1963 1
a1963 1
compile. For this, it is a convinient practice to include the required
@


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@
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@d28 1
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#                              read the listings of the object deck.
@


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@
text
@d151 5
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pth_writev_ev.
d173 5
a177 1
pth_pwrite.
d1541 32
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@


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@
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@d915 4
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particular cooperating thread.  If I<tid> is not C<NULL> and points to a
I<ready> thread, it is guaranteed that this thread receives execution control
on the next dispatching step. If I<tid> is in a different state (that is, still
not I<ready>) this has no effect and is equal to calling this function with
I<tid> specified as C<NULL>.
d921 2
a922 2
C<errno> set to C<EINVAL>) if I<tid> specified and invalid or still not ready
thread.
@


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@
text
@d1011 1
a1011 1
=item pth_time_t B<pth_time>(int I<sec>, int I<usec>);
d1017 1
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=item pth_time_t B<pth_timeout>(int I<sec>, int I<usec>);
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The thread stack size in bytes. Use lower values than 32KB with great care!
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C<PTH_CANCEL_DEFAULT>, C<PTH_ATTR_STACK_SIZE> := 32*1024 and
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     pth_attr_set(attr, PTH_ATTR_STACK_SIZE, 32*1024);
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awakened and stores the value of I<tid>'s pth_exit(3) call into I<value> and
returns to the caller. A thread can be joined only when it was I<not> spawned
with C<PTH_FLAG_NOJOIN>. A thread can only be joined once, i.e., after the
pth_join(3) call the thread I<tid> is removed from the system.
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threads.  The following attribute fields exists in attribute objects:
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This sets the attribute field I<field> in I<attr> to a value specified as an
additional argument on the variable argument list. The following
attribute fields exists:
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a826 2
This destroys a attribute object I<attr>. After this I<attr> is no longer a
valid attribute object.
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B<Pth> (intentionally) provides no replacements for thread-safe
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B<Pth> installation via its C<pth-config> program. This approach works fine
for small projects.
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The previous approach is simple but unflexible. First, to speed up building it
would be nice to not expand the compiler and linker flags every time the
compiler is started. Second, it would be useful to also be able to build
against an uninstalled B<Pth>, that is, against a B<Pth> source tree which was
just configured and built, but not installed. Third, it would be also useful
to allow checking of the B<Pth> version to make sure it is at least a minimum
required version. And finally, it would be also great to make sure B<Pth>
works correctly by first performing some sanity compile and run-time checks.
All this can be done if we use GNU B<autoconf> and the C<AC_CHECK_PTH> macro
provided by B<Pth>.  For this, we establish the following three files:
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C<distclean> target which cleans up this, too.  Second, we write a
(minimalistic) B<autoconf> script specification in a file C<configure.in>:
d1814 1
a1814 1
 | AC_CHECK_PTH(1.2.0)
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If we now run C<configure> we get a correct C<Makefile> which immediately can
be used to build C<foo> (assuming that B<Pth> is already installed somewhere):
d1846 1
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 checking for GNU Pth... version 1.2.0, installed under /usr/local
d1852 8
a1859 2
 gcc -g -O2 -I/sw/pkg/pth/include -c foo.c
 gcc -L/sw/pkg/pth/lib -o foo foo.o -lpth
d1917 1
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 | AC_CHECK_PTH(1.2.0, subdir:pth --disable-tests)
d1931 4
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Now we let B<autoconf>'s C<aclocal> program again generate an C<aclocal.m4>
file for us with the contents of B<Pth>'s C<AC_CHECK_PTH> macro and finally we
generate the C<configure> script out of this C<aclocal.m4> file and the
C<configure.in> file:
d1990 1
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 checking for GNU Pth... version 1.3a1, local under pth
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As you can see B<autoconf> now automatically configures the local (stripped
down) copy of B<Pth> in the subdirectory C<pth/> and the C<Makefile>
automatically builds the subdirectory, too.
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The following example is a useless server which does nothing more
than listening on a TCP port (specified numerically on the command
line) and displaying the current time to the socket when a connection
was established. For each incoming connection a thread is spawned.
Additionally, to see more multithreading, a useless ticker thread
runs simultaneously which outputs the current time to C<stderr> every
5 seconds. The example contains I<no> error checking and is I<only>
intended to show you the look and feel of B<Pth>.
d1672 2
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     if (argc != 2) {
         fprintf(stderr, "Usage: %s <port>\n", argv[0]);
         exit(1);
     }

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     port = atoi(argv[1]);
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     sar.sin_port = htons(port);
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traditional approach to achieve tread-safety is to wrap a function body
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side-effects from within a signal handler context. Usually very less
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function after each other controlled by this matrix. The threads
are created by more than one jump-trail through this matrix and by
switching the individual jump-trails between function calls controlled
by corresponding occurred events.
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kills the treading system and returns C<TRUE>.
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just made pending. But when its C<PTH_CANCEL_ASYNCHRONOUS> the tread is
d1714 5
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=item C<PTH_EVENT_PID>

This is a process event. Three additional arguments have to be given which
correspond to the arguments of the waitpid(2) function: `C<pid_t>', `C<int
*>' and `C<int>'.  This events waits until the process changed to the
specified state.  Example: `C<pth_event(PTH_EVENT_PID, pid, &status, 0)>'.

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This is a custom callback function event. Two additional arguments have to be
given with the following types: `C<int (*)(void *)>' and `C<void *>'. The
first is a function pointer and the second is an argument which is passed to
the function. The scheduler calls this function on a regular basis (on his own
scheduler stack, so be careful!) and the thread is kept sleeping while the
function returns 0. Once it returned not 0 the thread will be awakend.
Example: `C<pth_event(PTH_EVENT_FUNC, func, arg)>'.
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similar to the POSIX Pthread API. Use this for thread specific global data.
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July 1999 by I<Ralf S. Engelschall> after evaluating various (mostly
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performance) with an API similar to the popular one found in Pthread
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So the essential idea for the non-preemptive approach was taken over
from I<Peter Simons> scheduler. The priority based scheduling algorithm
was contributed by I<Martin Kraemer>. Some code inspiration also came
from an experimental threading library (B<rsthreads>) written by
I<Robert S. Thau> for an ancient internal test version of the Apache
webserver. The concept and API of message ports was borrowed from
AmigaOS' B<Exec> subsystem. The concept and idea for the flexible event
mechanism came from I<Paul Vixie>'s B<eventlib> (which can be found as a
part of B<BIND> v8).
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execution (aka "multithreading") inside event-driven applications. All threads
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("Pthreads") which can be used for backward compatibility to existing
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machines, we use "multitasking" -- that is, we have the application
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with an internal mutual exclusion lock (aka "mutex"). As you should
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concept of "coroutines". On the other hand, event driven applications
d526 1
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priority of all remaining threads by 1, to prevent them from "starving".
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unit of the current process into a thread (the "main" thread). It
d600 1
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``C<pth_exit(0);>'' in the main thread (which waits for all other threads to
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``C<pth_kill(); exit(0)>'' (which immediately kills the threading system and
d622 11
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C<PTH_CTRL_GETTHREADS_NEW> for the number of threads in the new queue (threads
created via pth_spawn(3) but still not scheduled once),
C<PTH_CTRL_GETTHREADS_READY> for the number of threads in the ready queue
(threads who want to do CPU bursts), C<PTH_CTRL_GETTHREADS_RUNNING> for the
number of running threads (always just one thread!),
C<PTH_CTRL_GETTHREADS_WAITING> for the number of threads in the waiting queue
(threads waiting for events), C<PTH_CTRL_GETTHREADS_DEAD> for the number of
threads in the new queue (terminated threads waiting for a join).
d636 1
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This requires a second argument of type ``C<float *>'' (pointer to a floating
d647 1
a647 1
This requires a second argument of type ``C<pth_t>'' which identifies a
d653 1
a653 1
This requires a second argument of type ``C<pth_t>'' which identifies a
d655 1
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pth_ctrl(3) should be casted to a ``C<char *>''.
d659 1
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This requires a second argument of type ``C<FILE *>'' to which a summary
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This function returns a hex-value ``0xI<V>I<RR>I<T>I<LL>'' which describes the
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C<PTH_ATTR_PRIO> := C<PTH_PRIO_STD>, C<PTH_ATTR_NAME> := "C<unknown>",
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``pth_exit(I<entry>(I<arg>))'' inside the new thread unit, i.e., I<entry>'s
d831 1
a831 1
as ``I<func>(I<arg>)'' in the system. In other words: Only the first call to
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I<ctrlvar> should be declared as ``C<pth_once_t> I<variable-name> =
C<PTH_ONCE_INIT>;'' before calling this function.
d868 1
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performed, i.e., ``C<pth_raise(tid, 0)>'' returns C<TRUE> when thread I<tid>
d932 1
a932 1
``C<pth_exit(PTH_CANCELED)>'' at one of his cancellation points.  In B<Pth>
d939 1
a939 1
waits to be joined it just joins it (via ``C<pth_join(>I<tid>C<, NULL)>'') and
d942 1
a942 1
``C<pth_cancel(>I<tid>C<)>''.
d1038 1
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``C<pth_exit(PTH_CANCELED)>''.
d1064 1
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``C<pth_event(PTH_EVENT_FD|PTH_UNTIL_FD_READABLE, fd)>''.
d1078 3
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Example: ``C<pth_event(PTH_EVENT_SELECT, &rc, nfd, rfds, wfds, efds)>'' where
C<rc> has to be of type ``C<int *>'', C<nfd> has to be of type ``C<int>'' and
C<rfds>, C<wfds> and C<efds> have to be of type ``C<fd_set *>'' (see
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to a signal set (type ``C<sigset_t *>'') and a pointer to a signal number
variable (type ``C<int *>'').  This event waits until one of the signals in
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your notice. Example: ``C<sigemptyset(&set); sigaddset(&set, SIGINT);
pth_event(PTH_EVENT_SIG, &set, &sig);>''.
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``C<pth_event(PTH_EVENT_TIME, pth_timeout(2,0))>''.
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on the specified message port.  Example: ``C<pth_event(PTH_EVENT_MSG, mp)>''.
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``C<pth_event(PTH_EVENT_TID|PTH_UNTIL_TID_DEAD, tid)>''.
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correspond to the arguments of the waitpid(2) function: ``C<pid_t>'', ``C<int
*>'' and ``C<int>''.  This events waits until the process changed to the
specified state.  Example: ``C<pth_event(PTH_EVENT_PID, pid, &status, 0)>''.
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given with the following types: ``C<int (*)(void *)>'' and ``C<void *>''. The
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Example: ``C<pth_event(PTH_EVENT_FUNC, func, arg)>''.
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To make it clear, when you constructed I<ev> via ``C<ev =
pth_event(PTH_EVENT_FD, fd);>'' you have to extract it via
``C<pth_event_extract(ev, &fd)>'', etc. For multiple arguments of an event the
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This dynamically initializes a mutex variable of type ``C<pth_mutex_t>''.
Alternatively one can also use static initialization via ``C<pth_mutex_t
mutex = PTH_MUTEX_INIT>''.
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``C<pth_rwlock_t>''.  Alternatively one can also use static initialization
via ``C<pth_rwlock_t rwlock = PTH_RWLOCK_INIT>''.
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``C<pth_cond_t>''.  Alternatively one can also use static initialization via
``C<pth_cond_t cond = PTH_COND_INIT>''.
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This dynamically initializes a barrier variable of type ``C<pth_barrier_t>''.
Alternatively one can also use static initialization via ``C<pth_barrier_t
barrier = PTH_BARRIER_INIT(>I<threadhold>C<)>''.
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API, i.e., they are similar to the functions under "B<Standard POSIX
Replacement API>" but all have an additional event argument which can be used
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The following example is a useless server which does nothing more than
listening on a specified TCP port and displaying the current time to the
socket when a connection was established. For each incoming connection a
thread is spawned. The example contains I<no> error checking and is I<only>
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d1691 1
d1708 1
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to read(3) ``magically'' means pth_read(3). The problem here is that such
d2133 1
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fix the problem and include a patch, made with ``C<diff -u3>'', in your
d2139 2
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I<pth-users-request@@gnu.org> with ``C<subscribe pth-users>'' (or
``C<subscribe pth-users> I<address>'' if you want to subscribe
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``comp.programming.threads Newsgroup Archive'',
d2154 1
a2154 1
``comp.programming.threads Frequently Asked Questions (F.A.Q.)'',
d2157 1
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``I<Multithreading - Definitions and Guidelines>'',
d2161 1
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``I<The Single UNIX Specification, Version 2 - Threads>'',
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``I<Pthreads Programming - A POSIX Standard for Better Multiprocessing>'',
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``I<Multithreaded Programming with Pthreads>'',
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``I<Threads Primer - A Guide To Multithreaded Programming>'',
d2191 1
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``I<Thread Time - The Multithreaded Programming Guide>'',
d2196 1
a2196 1
``I<Programming with POSIX Threads>'',
d2204 1
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sigprocmask(2).  sigsuspend(2), sigsetjmp(3), siglongjmp(3), setjmp(3),
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pth_sfiodisc,
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scheduler. The intention is, that this way both better portability and run-time
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multithreaded applications.
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regular jobs and one-shot requests have to processed in parallel.
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of memory).
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(one has to use atomic locks, etc). The machine's resources can be
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load because of these resource problems. In practice, lot's of tricks
are usually used to overcome these problems (ranging from pre-forked
sub-process pools to semi-serialized processing, etc).
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One the most elegant ways to solve these resource- and data-sharing
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processes. Threads are neither the optimal runtime facility for all
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descriptors>, I<signal table>. On every process switch, the kernel
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called light-weight processes / LWP).
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User-space threads are usually more portable and can perform faster and
cheaper context switches (for instance via setjmp(3)/longjmp(3)) than
kernel based threads. On the other hand, kernel-space threads can take
advantage of multiprocessor machines and don't have any I/O blocking
problems. Kernel-space threads are usually scheduled in preemptive way
side-by-side with the underlying processes. User-space threads on the
other hand use either preemptive or non-preemptive scheduling.
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In preemptive scheduling the scheduler lets a thread execute until
a blocking situation occurres (usually a function call which would
block) or the assigned timeslice elapses. Then it detracts control from
the thread without a chance for the thread to object. This is usually
realized by interrupting the thread through a software signal (like
C<SIGALRM> or C<SIGVTALRM>). In non-preemptive scheduling, once a thread
received control from the scheduler it keeps it until either a blocking
situation occurs (again a function call which would block and instead
switches to the scheduler) or the thread explicitly yields control back
to the scheduler in a cooperative way.
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Responsiveness of a system can be described by the user visible delay until
the system responses to an external request. When this delay is small enough
and the user doesn't recognize a noticeable delay, the responsiveness of the
system is considered good. When the user recognizes or is even annoyed by the
delay, the responsiveness of the system is considered bad.
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=item B<o> B<reentrant>, B<thread-safe> and B<async-safe> functions
d321 30
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simultaneously by several threads. Functions that access global state,
such as memory or files, of course, need to be carefully designed
in order to be reentrant. Two traditional approaches to solve these
problems are caller-supplied states and thread-specific data.

Thread-safety is the avoidance of I<data races>, i.e., situations in
which data is set to either correct or incorrect value depending upon
the (unpredictable) order in which multiple threads access and modify
the data. So a function is thread-safe when it behaves semantically
correct when executed by several threads. As you should recognize,
reentrant is a slightly stronger attribute than thread-safe, because it
is usually harder to achieve.

Additionally there is a related attribute named I<asynchronous-safe> which
comes into play in conjunction with signal handlers. This is very related to
the problem of I<reentrant> functions. An I<asynchronous safe> function is one
that can be called safe and without side-effects from within a signal handler
context. Usually very less functions are of this type. The problem
is that an application is very restricted in what it can perform
from within a signal handler, because only a few POSIX functions are
officially declared as and guaranteed to be async-safe.
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execution units (each runs for no more than a few milliseconds) and
those units are implemented by separate functions. Then a global
matrix is defined which describes the execution (and perhaps even
dependency) order of these functions. The main server procedure then
just dispatches between these units by calling one function after each
other controlled by this matrix. The threads are created by more than
one jump-trail through this matrix and by switching the threads between
these jump-trails controlled by corresponding occurred events.
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This approach gives the best possible performance because one can
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The disadvantage of this approach is that it is complicated to write large
applications with this approach, because in those applications one quickly
gets hundreds(!) of execution units and the control flow inside such an
application is very hard to understand (because it is interrupted by
function borders and one always has to remember the global dispatching
matrix to follow it). Additionally all threads operate on the same
execution stack. Although this saves memory it is often nasty because
one cannot switch between threads in the middle of a function. Thus the
scheduling borders are the function borders.
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Actually in a preemptive way similar to what the kernel does for the
heavy-weight processes, i.e., every few milliseconds the scheduler
switches between the threads of execution. But the thread itself doesn't
recognize this and usually (except for synchronization issues) doesn't
have to care about this.
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Additionally the programming is very similar to a fork(2) based
approach.
d413 1
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compared to using approaches with heavy-weight processes, it is decreased
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Finally there is no really portable POSIX/ANSI-C based way to implement
user-space preemptive threads. Either the platform already has threads,
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even those semi-portable packages have to deal with assembler code and
other nasty internals and are not easy to port to forthcoming platforms.
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So, in short: The matrix-dispatching approach is portable and fast, but
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This is because it uses a nifty and portable POSIX/ANSI-C approach for
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hand this way not all fancy threading features can be implemented.
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The reason is the non-preemptive scheduling. Number-crunching applications
usually require preemptive scheduling to achieve concurrency because of their
long CPU bursts. For them non-preemptive scheduling (even together with explicit
yielding) provides only the old concept of "coroutines". On the other hand,
event driven applications benefit greatly from non-preemptive scheduling. They
have only short CPU bursts and lots of events to wait on and this way run
faster under preemptive scheduling because of no unnecessary context switching
occurs as it is the case for preemptive scheduling. That's why B<Pth> is
mainly intended for server type applications.
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reentered before it returned. This is a great portability benefit, because
thread-safety can be achieved more easily than reentrance possibility.
Especially this means that under B<Pth> more existing third-party libraries
can be used without side-effects than its the case for other threading
systems.
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benefit from the existence of multiprocessors, because for this kernel
support would be needed. In practice, this is no problem because
multiprocessor systems are rare, and portability is more important than
highest concurrency.
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To understand the B<Pth> API it helps to first understand the life cycle
of a thread in the B<Pth> threading system. It can be illustrated with
the following graph:
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scheduler.  On the next dispatching, the scheduler picks it up from there and
moves it to the B<READY> queue. This is a queue containing all threads which
want to perform a CPU burst. There they are queued in priority order.  On each
dispatching step, the scheduler always removes the thread with the
highest priority only. It then increases the priority of all remaining
threads by 1, to prevent them from "starving".

The thread which was removed from the B<READY> queue is the new B<RUNNING>
thread (there is always just one B<RUNNING> thread, of course). The B<RUNNING>
thread is assigned execution control. After this thread yields execution
(either explicitly or implicitly by calling a function which would block)
there are three possibilities: Either it has terminated, then it is moved to
the B<DEAD> queue, or it has events on which it wants to wait, then it is
moved into the B<WAITING> queue. Else it is assumed it wants to perform more
CPU bursts and enters the B<READY> queue again.
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B<WAITING> queue is checked for pending events. If one or more events of
a thread occurred, the threads that are waiting on them are immediately
moved to the B<READY> queue.

The purpose of the B<NEW> queue has to do with the fact that a thread
never directly switches to another thread. A thread always yields
execution to the scheduler and the scheduler dispatches to the next
thread. So a freshly spawned thread has to be kept somewhere until the
scheduler gets a chance to pick it up for scheduling. That is for what
the B<NEW> queue is for. The purpose of the B<DEAD> queue is to support
thread joining. When a thread is marked to be unjoinable, it is directly
kicked out of the system after it terminated. But when it is joinable it
enters the B<DEAD> queue. There it remains until another thread joins
it.
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Finally there is a special separated queue named B<SUSPENDED> to where
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queue by the application. The purpose of this special queue is to
d562 2
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from where it originally came.
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=head1 APPLICATION PROGRAMMERS INTERFACE
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In the following the B<Pth> I<Application Programming Interface> (API) is
discussed in detail. With the knowledge given above it should be now easy to
understand how to program threads with this API.
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execution (aka `multithreading') inside event-driven applications. All threads
d557 2
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unit of the current process into a thread (the "main" thread).
d571 3
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terminates the process). The pth_kill() return immediately with a return code
of C<FALSE> if it is called not from within the main thread. Else kills the
treading system and returns C<TRUE>.
d630 2
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keeps track of thread in dynamic data structures.
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                     V
                   DEAD
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provided by B<Pth>.  For this we establish the following three files:
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compile. For this it is a convinient practice to include the required
d1889 1
a1889 1
Now we have to create the C<pth/> subdirectory itself. For this we extract the
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a1993 4
The drawback of this approach is just that really all source files of the
application where these function calls occur have to include C<pth.h>, of
course. And this also means that this way existing libraries, including the
vendor's B<stdio> usually will still block the whole process.
d2005 7
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The drawback of this approach is that it depends on syscall(2) and that
prototype conflicts can occur while building the wrapper functions due to
different function signatures in the vendor headers. But the advantage of this
mapping variant is that the source files of the application where these
function calls occur have not to include C<pth.h> and that existing libraries,
including the vendor's B<stdio>, magically become thread-aware.
d2015 31
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B<Pth> is very portable because it has only one part which perhaps has to be
ported to new platforms (the machine context initialization). But it is
written in a way which works on mostly all Unix platforms which support
sigstack(2) or sigaltstack(2) [see C<pth_mctx.c> for details]. Any other code
is straight-forward POSIX and ANSI C based.

The context switching is done via POSIX [sig]setjmp(3) and [sig]longjmp(3).
Here all CPU registers, the program counter and the stack pointer are
switched. Additionally the B<Pth> dispatcher switches also the global Unix
C<errno> variable [see C<pth_mctx.c> for details] and the signal mask (either
implicitly via sigsetjmp(3) or in an emulated way via explicit setprocmask(2)
calls).

The B<Pth> event manager is mainly select(2) and gettimeofday(2) based, i.e.,
the current time is fetched via gettimeofday(2) once per context switch for
calculations and both the time and all I/O events are implemented via a single
select(2) call [see C<pth_sched.c> for details].

The thread control block management is done via priority queues without any
additional data structure overhead. For this the queue linkage attributes are
part of the thread control blocks and the queues are actually implemented as
rings with a selected element as the entry point [see C<pth_tcb.h> and
C<pth_pqueue.c> for details].

Most time critical sections (especially the dispatcher and event manager) are
speeded up by inlined functions (implemented as ANSI C pre-processor macros).
Additionally any debugging code is I<completely> removed from the source when
not built with C<-DPTH_DEBUG> (see Autoconf C<--enable-debug> option), i.e.,
not only stub functions remain [see C<pth_debug.h> for details].
d2050 9
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functions (like strtok(3) which uses a static internal buffer) or synchronous
system functions (like gethostbyname(3) which doesn't provide an asynchronous
mode where it doesn't block). When you want to use those functions in your
server application together with threads you've to either link the application
against special third-party libraries (or for thread-safe/reentrant functions
possibly against an existing C<libc_r> of the platform vendor).  For an
asynchronous DNS resolver library use either the C<libresolv> from B<BIND
8> ( see ftp://ftp.isc.org/isc/bind/ ) or the forthcoming GNU B<adns> package
from Ian Jackson ( see http://www.gnu.org/software/adns/adns.html ).
d2062 21
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The B<Pth> library was designed and implemented between February and July 1999
by I<Ralf S. Engelschall> after evaluating various (mostly preemptive) thread
libraries and intensive discussions with I<Peter Simons>, I<Martin Kraemer>,
I<Lars Eilebrecht> and I<Ralph Babel> related to an experimental (matrix
based) non-preemptive C++ scheduler class written by I<Peter Simons>.

B<Pth> was then implemented in order to combine the I<non-preemptive> approach
of multithreading (providing better portability and performance) with an API
similar to the one found in POSIX thread libraries (providing easy
programming).

So the essential idea for the non-preemptive approach was taken over from
I<Peter Simons> scheduler. The priority based scheduling algorithm was
contributed by I<Martin Kraemer>. Some code inspiration also came from an old
threading library (B<rsthreads>) written by I<Robert S. Thau> for an ancient
internal test version of Apache. The concept and API of message ports was
borrowed from AmigaOS' B<Exec>. The concept and idea for the flexible event
mechanism came from I<Paul Vixie>'s B<eventlib> (part of B<BIND8>).
d2087 13
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complete as possible to I<bug-pth@@gnu.org>. If you can, please try to fix the
problem and include a patch, made with ``C<diff -u3>'', in your report.
Always at least include a reasonable amount of description in your report to
allow the author to reproduce the bug.

For further support you additionally can subscribe yourself to the
I<pth-users@@gnu.org> mailing list by sending a mail to
I<pth-users-request@@gnu.org> with ``C<subscribe pth-users>'' in the body.
Then you can discuss your issues with other B<Pth> users by sending messages
to I<pth-users@@gnu.org>.
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runs in the same address space of the application process, but each thread has
its own individual program-counter, run-time stack, signal mask and errno
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Additionally B<Pth> provides an optional emulation API for POSIX.1c threads
("pthreads") which can be used for backward compatibility to existing
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When programming event driven applications, usually servers, lots of regular
jobs and one-shot requests have to processed in parallel. To achieve this in
an efficient way on uniprocessor machines the idea of multitasking is
implemented by the operating system which can be used by the applications to
spawn multiple instances of itself. On Unix the kernel classically implements
multitasking in a preemptive and priority-based way through heavy-weight
processes spawned with fork(2). These processes do usually I<not> share a
common address space. Instead they are clearly separated from each other and
were created by direct cloning a process address space (although modern
kernels use memory segment mapping and copy-on-write semantics to avoid
unnecessary copying of memory).

The drawbacks are obvious: Sharing data between the processes is complicated
and can usually only solved in an efficient way through shared memory (but
which itself is not very portable). Synchronization is complicated because of
the preemptive nature of the Unix scheduler (one has to use atomic locks,
etc). The machine resources can be exhausted very quickly when the server
application has to serve too much longer running requests (heavy-weight
processes cost memory). Additionally when for each request a sub-process is
spawned to handle it, the server performance and responsiveness is horrible
(heavy-weight processes cost time to spawn).  And finally the server
application doesn't scale very well with the load because of these resource
problems. Lot's of tricks are usually done in practice to overcome these
problems (ranging from pre-forked sub-process pools to semi-serialized
processing, etc).

One the most elegant ways to solve these resource and data sharing problems is
to have multiple I<light-weight> threads of execution inside a single
(heavy-weight) process, i.e., to use I<multithreading>.  Those I<threads>
usually improve responsiveness and performance of the application, often
improve and simplify the internal program structure and especially require
less system resources. Threads neither are the optimal runtime facility for
all types of applications nor can all applications gain from them. But at
least event driven server applications usually benefit greatly from using
threads.
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Lots of documents exists which describe and define the world of threading. To
understand B<Pth> only the basic knowledge about threading is actually
required. The following definitions of thread related terms should at least
help you in understanding the programming context of threads in order to allow
you to use B<Pth>.
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A process on Unix systems consist of at least the following fundamental
ingredients: I<virtual memory table>, I<program code>, I<program counter>,
I<heap memory>, I<stack memory>, I<stack pointer>, I<file descriptors>,
I<signal table>. On every process switch the kernel saves and restores these
ingredients for the individual processes. On the other hand a thread consists
only of a private program counter, stack memory, stack pointer and signal
table. All other ingredients, especially the virtual memory, it shares with
the other threads of the same process.
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Threads on a Unix platform classically can be implemented either inside kernel
space or user space. When threads are implemented by the kernel, the thread
context switches are performed by the kernel without notice by the
application. When threads are implemented in user space, the thread context
switches are performed by an application library without notice by the kernel.
Additionally there exist also hybrid threading approaches where typically a
user-space library binds one or more user-space threads to one or more
kernel-space threads (there usually called light-weight processes / LWP).

User space threads are usually more portable and can perform faster and
cheaper context switches (for instance via setjmp(3)/longjmp(3)) than kernel
based threads. On the other hand, kernel space threads can take advantage of
multiprocessor machines and don't have any I/O blocking problems. Kernel-space
threads are usually always scheduled in preemptive way side-by-side with the
underlaying processes. User-space threads on the other hand use either
preemptive or non-preemptive scheduling.
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C<SIGALRM> or C<SIGVTALRM>). In non-preemptive scheduling once a thread
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=item B<o> B<concurrency> vs. B<paralleism>
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Concurrency exists when at least two threads are I<in progress> at the same
time. Parallelism arises when at least two threads are I<executing>
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machines, of course. But one also usually speaks of parallelism or I<high
concurreny> in the context of preemptive thread scheduling and of I<low
concurreny> in the context of non-preemptive thread scheduling.
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simultaneously by several threads. Functions that access global state, like
memory or files, have inherently reentrant problems, of course. Two classical
approaches to solve these problems are caller-supplied states and
thread-specific data.

Thread-safety is the avoidance of I<data races>, i.e., situations in which data
is set to either correct or incorrect value depending upon the (unpredictable)
order in which multiple threads access and modify the data.  So a function is
thread-safe when it behaves logically correct when executed by several
threads. As you should recognize, reentrant is a stronger attribute than
thread-safe.
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context. Usually very less functions are of this type. The problem is that an
application is very restricted in what it can perform from within a signal
handler, because only a few POSIX functions are officially declared as and
guarrantied to be async-safe.
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=head2 User-Land Threads
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User-land threads can be implemented in various way. The two classical
approaches are:
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execution units (each has to run maximal a few milliseconds) and those units
are implemented by separate program functions. Then a global matrix is created
which describes the execution (and perhaps even dependency) order of these
functions. The main server procedure then does just dispatching between these
units by calling one function after each other controlled by this matrix.  The
treads are created by more than one jump-trail through this matrix and by
switching between these jump-trails controlled by corresponding occurred
events.

The advantage of this approach is that the performance is really as maximal as
possible (because one can fine-tune the threads of execution by adjusting the
matrix and the scheduling is done explicitly by the application itself).
Additionally this is very portable, because the matrix is just an ordinary
data structure and functions are a standard feature of ANSI C.
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applications with this approach, because in those applications one quickly get
hundreds(!) of execution units and the control flow inside such an application
is very hard to understand (because it is interrupted by function borders and
one always has to remember the global dispatching matrix to follow it).
Additionally all threads operate on the same execution stack. Although this
saves memory it is often nasty because one cannot switch between threads in
the middle of a function. The scheduling borders are function borders.
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B<Context-based based implicit scheduling between threads of execution:>
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Here the idea is that one programs the application as with fork(2)'ed
processes, i.e., one spawns a thread of execution and this runs from the begin
to the end without an interrupted control flow. But the control flow can be
still interrupted - even in the middle of a function.  Actually in a preemptive
way similar to what the kernel does for the heavy-weight processes, i.e., every
few milliseconds the scheduler switches between the threads of execution. But
the thread itself doesn't recognize this and usually (except for
synchronization issues) doesn't have to care about this.

The advantage of this approach is that it's usually very easy to program,
because the control flow and context of a thread directly follows a procedure
without forced interrupts through function borders. Additionally the
programming is very similar to a fork(2)'ed approach.
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scheduling does usually a lot more context switches (every user-land context
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user-space preemptive threads. Either the platform already has threads or one
has to hope that some semi-portable package exists for it. And even those
semi-portable packages have to deal with assembler code and other nasty
internals and are not easy to port to forthcoming platforms.
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So, in short: The matrix-dispatching approach is portable and fast, but nasty
to program. The thread scheduling approach is easy to program, but suffers
from synchronization and portability problems caused by its preemptive nature.
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But why not combine the good aspects of both discussed approaches while trying
to avoid their bad aspects? That's the general intention and goal of B<Pth>.
In detail this means that B<Pth> implements the easy to program threads of
execution but in a way which doesn't have the portability side-effects of
preemptive scheduling. This means that instead a non-preemptive scheduling is
used.

This sounds and is an interesting approach. Nevertheless one has to keep the
implications of non-preemptive thread scheduling in mind when working with
B<Pth>. The following list summarizes a few essential points:
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The reasons are mainly because it uses a nifty and portable POSIX/ANSI-C
approach for thread creation (and this way doesn't require any platform
dependent assembler hacks) and schedules the threads in non-preemptive way
(which doesn't require unportable facilities like C<SIGVTALRM>).  On the other
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B<Pth increases the responsiveness and concurrency of an event driven
application, but NOT the concurrency of number crunching applications>.
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The reason is the non-preemptive scheduling. Number crunching applications
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This means that B<Pth> runs on mostly all types of Unix kernels, because the
kernel does not even recognize the B<Pth> threads (because they are
implemented entirely in user-space).  On the other hand, it cannot benefit
from the existance of multiprocessors, because for this kernel support would
be needed. Practice this is no problem because multiprocessor systems are rare
and portability is more important than highest concurrency.
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To better understand the B<Pth> API it is reasonable to first understand the
life cycle of a thread in the B<Pth> threading system. It can be illustrated
with the following graph:
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      +---> READY----+
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scheduler.  On the next dispatching the scheduler picks it up from there and
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want to perform a CPU burst. There they are queued in priority order.  Per
dispatching step, the scheduler always removes the thread with the highest
priority only. The assigned queue priority for all remaining threads every
time is increased by 1 to prevent thread starvation.
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Before the next thread is taken out of the B<READY> queue, the B<WAITING>
queue is checked for pending events. When one or more events of a thread
occured, it is immediately moved to the B<READY> queue, too.

The purpose of the B<NEW> queue has to do with the fact that a thread never
directly switches to another thread. A thread always yields execution to the
scheduler and the scheduler dispatches to the next thread. The purpose of the
B<DEAD> queue is to support thread joining. When a thread is marked to be
unjoinable, it is directly kicked out of the system after it terminated. But
when it is joinable it enters the B<DEAD> queue. There is remains until
another thread joins it.
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disscussed in detail. With the knowledge given above it should be now easy to
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The following functions act on a global library basis.  They are used to
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This initializes the B<Pth> library. It has to be really the first B<Pth> API
function call in an application and is mandatory. It's usually done at the
begin of the main() function of the application. This implicitly spawns the
internal scheduler thread and transforms the single execution unit of the
current process into a thread (the "main" thread).
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the main function of the application. At least it has to be called from within
d554 1
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calling thread into the single execution unit of the underlaying process.  The
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=item long B<pth_ctrl>(unsigned lont I<query>, ...);
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signal to a thread and its guarranties that only this thread gets the signal
d822 1
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I<ready> thread, it is guarrantied that this thread receives execution control
d835 1
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a resolution of one microsecond. In pratice you should neither rely on this
d837 1
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only guarranties that the thread will sleep at least I<naptime>. But because
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the various pth_event_xxx() functions). It's modelled like select(2), i.e., one
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when one ore more of them occurred after tagging them as occured. The I<ev>
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tagging. pth_wait(3) returns the number of occured events and the application
can use pth_event_occurred(3) to test which events occured.
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performed. When its C<PTH_CANCEL_DEFERRED> again the calcellation request is
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immediately cancelled before pth_cancel(3) returns. The effect of a thread
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This is the crual way to cancel a thread I<tid>. When it's already dead and
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awakend and stores the value of I<tid>'s pth_exit(3) call into I<value> and
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This switches the non-blocking mode flag on filedescriptor I<fd>.  The
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longer a requirement to manually switch a filedescriptor into non-blocking
d913 1
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Instead when you now switch a filedescriptor explicitly into non-blocking
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This functions is always available, but only reasonably useable when B<Pth>
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This is a filedescriptor event. One or more of C<PTH_UNTIL_FD_READABLE>,
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I<spec> to specify on which state of the filedescriptor you want to wait.  The
filedescriptor itself has to be given as an additional argument.  Example:
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This is a multiple filedescriptor event modeled directly after the select(2)
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convinient way to wait for a large set of filedescriptors at once and at each
filedescriptor for a different type of state. Additionally as a nice
side-effect one receives the number of filedescriptors which causes the event
to be occurred (using BSD semantics, i.e., when a filedescriptor occurred in
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select(2)). The number of occurred filedescriptors are stored in C<rc>.
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When pth_event(3) is threated like sprintf(3), then this function is
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similar to the POSIX pthread API. Use this for thread specific global data.
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C<NULL>).  Recursive locking is explicity supported, i.e., a thread is allowed
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the whole process in case the filedescriptors will block.
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elapsed.  The thread is guarrantied to not awakened before this time, but
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thread is guarrantied to not awakened before this time, but because of the
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signal handler. Instead it's catched by the scheduler only in order to awake
d1538 1
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bytes into I<buf> from filedescriptor I<fd>.  The difference between read(2)
d1540 1
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thread until the filedescriptor is ready for reading. For more details about
d1546 1
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filedescriptor I<fd> into the first I<iovcnt> rows of the I<iov> vector.  The
d1548 1
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suspends execution of the current thread until the filedescriptor is ready for
d1555 1
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from I<buf> to filedescriptor I<fd>.  The difference between write(2) and
d1557 1
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thread until the filedescriptor is ready for writing.  For more details about
d1563 1
a1563 1
filedescriptor I<fd> from the first I<iovcnt> rows of the I<iov> vector.  The
d1565 1
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suspends execution of the current thread until the filedescriptor is ready for
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third-party stuff) this can be inconvinient.  Here it's required that a call
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##  Copyright (c) 1999 Ralf S. Engelschall <rse@@engelschall.com>
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=item void B<pth_kill>(void);
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the main function of the application. It implicitly kills all threads and
transforms back the calling thread into the single execution unit of the
underlaying process.
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##  This file is part of GNU Pth, a non-preemptive thread scheduling 
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#                            ``Real programmers don't document.  
#                              Documentation is for wimps who can't 
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pth_cleanup_push, 
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processing, etc). 
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thread-specific data. 
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guarrantied to be async-safe.  
d336 1
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B<Matrix-based explicit dispatching between small units of execution:> 
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events. 
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B<Context-based based implicit scheduling between threads of execution:> 
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used. 
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=item B<o> 
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B<Pth provides maximum portability, but NOT the fanciest features>. 
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=item B<o> 
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application, but NOT the concurrency of number crunching applications>. 
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=item B<o> 
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B<Pth requires thread-safe functions, but NOT reentrant functions>. 
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=item B<o> 
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benefit from multiprocessor machines>. 
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CPU bursts and enters the B<READY> queue again. 
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current process into a thread (the "main" thread). 
d787 1
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bursts into smaller units with this call. 
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=item pth_event_t B<pth_event>(unsigned long I<spec>, ...); 
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timeouts already can be handled via C<PTH_EVENT_TIME> events). 
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mutex to protect it, of course. 
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the event mechanism. 
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the whole process. 
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whole process. 
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desired position inside the file. 
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desired position inside the file. 
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 int main(int argc, char *argv[]) 
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 | 
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 | 
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accept(2), read(2), write(2).  
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accept(2), read(2), write(2). 
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is straight-forward POSIX and ANSI C based. 
d2006 1
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based) non-preemptive C++ scheduler class written by I<Peter Simons>. 
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programming). 
d2058 1
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Bibliography on threads and multithreading, 
d2065 2
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``I<Pthreads Programming - A POSIX Standard for Better Multiprocessing>'', 
O'Reilly 1996; 
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``I<Threads Primer - A Guide To Multithreaded Programming>'', 
Prentice Hall 1996; 
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##  pth.pod -- Pth manual page
##
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##  GNU Pth - The GNU Portable Threads
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##
##  pth.pod: Pth manual page
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the main function of the application. At least it has to be called from within
the main thread. It implicitly kills all threads and transforms back the
calling thread into the single execution unit of the underlaying process.  The
usual way to terminate a B<Pth> application is either a simple
``C<pth_exit(0);>'' in the main thread (which waits for all other threads to
terminate, kills the threading system and then terminates the process) or a
``C<pth_kill(); exit(0)>'' (which immediately kills the threading system and
terminates the process). The pth_kill() return immediately with a return code
of C<FALSE> if it is called not from within the main thread. Else kills the
treading system and returns C<TRUE>.
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         peer_len = sizeof(peer_addr);
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execution ("multithreading") inside even driven applications. All threads runs
in the same address space of the application process, but each thread has its
own individual program-counter, run-time stack, signal mask and errno
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The thread scheduling itself is done in a cooperative way, i.e. the threads
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scheduler. The intention is that this way both better portability and run-time
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(heavy-weight) process, i.e. to use I<multithreading>.  Those I<threads>
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Thread-safety is the avoidance of I<data races>, i.e. situations in which data
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processes, i.e. one spawns a thread of execution and this runs from the begin
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way similar to what the kernel does for the heavy-weight processes, i.e. every
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particular state, i.e. the C<PTH_CTRL_GETTHREADS> query is equal to the
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thread. It returns the name of the given thread, i.e. the return value of
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The thread cancellation state, i.e.  a combination of C<PTH_CANCEL_ENABLE> or
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The scheduling state of the thread, i.e. either C<PTH_STATE_NEW>,
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``pth_exit(I<entry>(I<arg>))'' inside the new thread unit, i.e. I<entry>'s
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performed, i.e.  ``C<pth_raise(tid, 0)>'' returns C<TRUE> when thread I<tid>
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times the threads should be cooperative, i.e. when they should split their CPU
d795 1
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on the next dispatching step. If I<tid> is in a different state (i.e.  still
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the various pth_event_xxx() functions). It's modelled like select(2), i.e. one
d855 1
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with C<PTH_FLAG_NOJOIN>. A thread can only be joined once, i.e.  after the
d935 1
a935 1
C<PTH_CANCEL_ASYNCHRONOUS> for allowing asynchronous cancellations, i.e.
d978 1
a978 1
to be occurred (using BSD semantics, i.e. when a filedescriptor occurred in
d1052 1
a1052 1
sscanf(3), i.e. it is the inverse operation of pth_event(3). This means that
d1211 2
a1212 2
calls to pth_atfork_push(3), i.e. FIFO. The I<prepare> fork handlers are
called in the opposite order, i.e. LIFO.
d1223 1
a1223 1
is forked into a separate process, i.e. in the parent process nothing changes
d1261 1
a1261 1
C<NULL>).  Recursive locking is explicity supported, i.e. a thread is allowed
d1336 1
a1336 1
API, i.e. they are similar to the functions under "B<Standard POSIX
d1701 1
a1701 1
The B<Pth> event manager is mainly select(2) and gettimeofday(2) based, i.e.
d1715 1
a1715 1
not built with C<-DPTH_DEBUG> (see Autoconf C<--enable-debug> option), i.e.
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##  version 2 of the License, or (at your option) any later version.
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in the same address space of the application process, but each thread has it's
@


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In the following the B<Pth> I<Application Programmers Interface> (API) is
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@d197 1
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implemented by the operation system which can be used by the applications to
d1752 1
a1752 1
=head1 BUG REPORTS
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@d616 1
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=item C<PTH_ATTR_NAME> (read-write) [B<char *>]
d736 8
a743 7
C<PTH_ATTR_DEFAULT> for default attributes) with the starting point at routine
I<entry>. This entry routine is called as ``pth_exit(I<entry>(I<arg>))''
inside the new thread unit, i.e. I<entry>'s return value is fed to an implicit
pth_exit(3). So the thread usually can exit by just returning. Nevertheless
the thread can also exit explicitly at any time by calling pth_exit(3). But
keep in mind that calling the POSIX function exit(3) still terminates the
complete process and not just the current thread.
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=item int B<pth_connect_ev>(int I<s>, const struct sockaddr *I<addr>, int I<addrlen>, pth_event_t I<ev>);
d1357 1
a1357 1
=item int B<pth_accept_ev>(int I<s>, struct sockaddr *I<addr>, int *I<addrlen>, pth_event_t I<ev>);
d1471 1
a1471 1
=item int B<pth_connect>(int I<s>, const struct sockaddr *I<addr>, int I<addrlen>);
d1480 1
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=item int B<pth_accept>(int I<s>, struct sockaddr *I<addr>, int *I<addrlen>);
@


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##  modify it under the terms of the GNU Library General Public
d17 1
a17 1
##  Library General Public License for more details.
d19 1
a19 1
##  You should have received a copy of the GNU Library General Public
@


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@d616 1
a616 1
=item C<PTH_ATTR_NAME> (read-write) [C<char *>]
d736 7
a742 8
C<PTH_ATTR_DEFAULT> for default attributes - which means that thread priority,
joinability and cancel state are inherited from the current thread) with the
starting point at routine I<entry>. This entry routine is called as
``pth_exit(I<entry>(I<arg>))'' inside the new thread unit, i.e. I<entry>'s
return value is fed to an implicit pth_exit(3). So the thread usually can exit
by just returning. Nevertheless the thread can also exit explicitly at any
time by calling pth_exit(3). But keep in mind that calling the POSIX function
exit(3) still terminates the complete process and not just the current thread.
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=item void B<pth_yield>(void);
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This explicitly yields back the execution to the scheduler thread.  Usually
the execution is transferred back to the scheduler when a thread waits for an
event. But when a thread has to do larger CPU bursts, it can be reasonable to
interrupt it explicitly by doing a few pth_yield() calls to give other threads
a chance to execute, too.  This obviously is the cooperating part of B<Pth>.
A thread I<has not> to yield execution, of course. But when you want to
program a server application with good response times the threads should be
cooperative, i.e. when they should split their CPU bursts into smaller units
with this call.
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structure when it is no longer needed.
@


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a1583 1
         printf("ticker: time: %s, average load: %.2f\n", ct, pth_load());
@


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@d1244 1
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returns C<FALSE> with C<errno> set to C<EAGAIN>.
d1265 1
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execution. Instead it returns C<FALSE> with C<errno> set to C<EAGAIN>.
@


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a74 1
pth_timeout.
d880 13
@


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@
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@d861 1
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C<PTH_FDMODE_ERROR> on error. Keep in mind that since Pth 1.1 there is no
d863 1
a863 1
mode in order to use it. This is automatically done temporarily inside Pth.
@


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@d129 3
a131 1
pth_cond_notify.
d1200 6
a1205 5
locks (mutex), read-write locks (rwlock) and condition variables (cond). Keep
in mind that in a non-preemptive threading system like B<Pth> this might sound
unnecessary at the first look, because a thread isn't interrupted by the
system. Actually when you have a critical code section which doesn't contain
any pth_xxx() functions, you don't need any mutex to protect it, of course. 
d1211 1
a1211 1
the event mechanism.
d1278 17
@


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@
text
@d71 1
a71 1
pth_nonblocking,
d852 1
a852 1
=item int B<pth_nonblocking>(int I<fd>);
d854 10
a863 2
This switches filedescriptor I<fd> into non-blocking mode which is a
prerequisite to use it together with the B<Pth> library.
a1529 1
     pth_nonblocking(fd);
a1572 1
     pth_nonblocking(sa);
@


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@
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@d1219 1
a1219 1
returns C<FALSE> with C<errno> set to C<EBUSY>.
d1240 1
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execution. Instead it returns C<FALSE> with C<errno> set to C<EBUSY>.
@


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@d1559 1
a1559 1
     pth_attr_set(attr, PTH_ATTR_NAME, "ticker")
d1573 1
a1573 1
     pth_attr_set(attr, PTH_ATTR_NAME, "handler")
@


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@d729 1
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C<PTH_ATTR_NONE> for no attributes) with the starting point at routine
@


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@
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@d793 1
a793 1
=item int B<pth_wait>(pth_event_t *I<ev>);
@


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@d726 1
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=item pth_t B<pth_spawn>(pth_attr_t *I<attr>, void *(*I<entry>)(void *), void *I<arg>);
@


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@


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text
@d1685 8
@


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@d1202 1
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This dynamically initializes a mutex variable of type ``C<pth_mutex_t *>''.
d1204 1
a1204 1
*mutex = PTH_MUTEX_INITIALIZER>''.
d1225 2
a1226 2
``C<pth_rwlock_t *>''.  Alternatively one can also use static initialization
via ``C<pth_rwlock_t *rwlock = PTH_RWLOCK_INITIALIZER>''.
d1245 2
a1246 2
``C<pth_cond_t *>''.  Alternatively one can also use static initialization via
``C<pth_cond_t *cond = PTH_COND_INITIALIZER>''.
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function to avoid temporary structure values.
@


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a141 1
pth_write_ev.
d155 5
a159 1
pth_write.
d1315 8
d1331 8
d1440 9
d1456 25
@


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@
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@d139 1
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pth_write_ev,
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a153 1
pth_write,
d1602 1
a1602 1
The B<Pth> library was designed and implemented between February and June 1999
@


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@d1530 1
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usleep(3), sleep(3), sigwait(3), waitpid(2), select(2), poll(2), connect(2),
@


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@d160 5
a164 4
provides non-preemptive scheduling for multiple threads of execution
("multithreading") inside even driven applications. All threads runs in the
same address space of the application process, but each thread has it's own
individual program-counter, run-time stack, signal mask and errno variable.
@


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@a138 1
pth_readline_ev.
a152 1
pth_readline.
a1307 8
=item ssize_t B<pth_readline_ev>(int I<fd>, void *I<buf>, size_t I<buflen>, pth_event_t I<ev>);

This is equal to pth_readline(3) (see below), but has an additional event
argument I<ev>. When pth_readline(3) suspends the current threads execution it
usually only uses the I/O event on I<fd> to awake. With this function any
number of extra events can be used to awake the current thread (remember that
I<ev> actually is an event I<ring>).

a1415 10

=item ssize_t B<pth_readline>(int I<fd>, void *I<buf>, size_t I<buflen>);

This is a convenience function which is based on pth_read(3).  It reads bytes
from filedescriptor I<fd> into I<buf> until a newline (``C<\n>'')is found, EOF
occurred or I<buflen> is reached. It internally uses thread-local buffering to
be able to read larger chunks of data. Do either use pth_read(3) I<or>
pth_readline(3) because pth_read(3) currently isn't aware of the buffering of
pth_readline(3). When you need generalized I/O with buffering then use a real
I/O library and let it use pth_read(3)/pth_write(3).
@


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@d137 1
d152 1
d1294 8
d1410 8
@


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@
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@d1531 2
a1532 2
usleep(3), sleep(3), sigwait(3), waitpid(2), select(2), connect(2), accept(2),
read(2), write(2).  
d1546 2
a1547 2
mapped: fork(2), sleep(3), waitpid(2), select(2), connect(2), accept(2),
read(2), write(2). 
@


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@d513 1
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This initializes the B<Pth> library. It has to be the first B<Pth> API
d1513 43
d1590 1
a1590 7
B<Pth> uses an explicit API (i.e. for instance you've to use pth_read(3) and
cannot just use read(3)) which might by nasty for some users. The reason is
because this way B<Pth> doesn't require any system call wrappers which usually
cannot be provided in a portable way. And portability is one of B<Pth>' major
goals.

Additionally B<Pth> (intentionally) provides no replacements for thread-safe
@


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@d136 1
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pth_write_ev,
d139 1
d150 1
a150 1
pth_write,
d153 1
d907 17
d1284 1
a1284 1
=item ssize_t B<pth_write_ev>(int I<fd>, const void *I<buf>, size_t I<nbytes>, pth_event_t I<ev>);
d1286 5
a1290 5
This is equal to pth_write(3) (see below), but has an additional event argument
I<ev>. When pth_write(3) suspends the current threads execution it usually
only uses the I/O event on I<fd> to awake. With this function any number of
extra events can be used to awake the current thread (remember that I<ev>
actually is an event I<ring>).
d1308 8
d1393 1
a1393 1
=item ssize_t B<pth_write>(int I<fd>, const void *I<buf>, size_t I<nbytes>);
d1395 5
a1399 5
This is a variant of the POSIX write(2) function. It writes I<nbytes> bytes
from I<buf> to filedescriptor I<fd>.  The difference between write(2) and
pth_write(2) is that that pth_write(2) suspends execution of the current
thread until the filedescriptor is ready for writing.  For more details about
the arguments and return code semantics see write(2).
d1418 8
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@d64 1
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@


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B<GNU Pth> - GNU Portable Threads
@


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@d576 2
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current PTH library version. I<V> is the version, I<RR> the revisions, I<LL>
the level and I<T> the type of the level (alphalevel=0, betalevel=1,
@


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@d7 1
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##  library library which can be found at http://www.gnu.org/software/pth/.
@


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@
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@d29 1
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B<Pth> - GNU Portable Threads
d33 1
a33 1
Pth PTH_VERSION_STR
@


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@
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@d6 2
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##  This file is part of GNU Pth, a non-preepmtive thread scheduling 
##  library which can be found at http://www.gnu.org/software/pth/.
@


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@
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@d2 1
a2 1
##  pth.pod -- PTH manual page
d6 2
a7 2
##  This file is part of PTH, a non-preepmtive thread scheduling library
##  which can be found at http://www.gnu.org/software/pth/.
d29 1
a29 1
B<GNU pth> - GNU Portable Threads
d33 1
a33 1
GNU pth PTH_VERSION_STR
d156 1
a156 1
B<PTH> is a very portable POSIX/ANSI-C based library for Unix platforms which
d171 1
a171 1
Additionally PTH provides an optional emulation API for POSIX.1c threads
d216 1
a216 1
understand B<PTH> only the basic knowledge about threading is actually
d219 1
a219 1
you to use B<PTH>.
d381 1
a381 1
=head2 The Compromise of PTH
d384 2
a385 2
to avoid their bad aspects? That's the general intention and goal of B<PTH>.
In detail this means that B<PTH> implements the easy to program threads of
d392 1
a392 1
B<PTH>. The following list summarizes a few essential points:
d398 1
a398 1
B<PTH provides maximum portability, but NOT the fanciest features>. 
d410 1
a410 1
B<PTH increases the responsiveness and concurrency of an event driven
d420 1
a420 1
occurs as it is the case for preemptive scheduling. That's why B<PTH> is
d425 1
a425 1
B<PTH requires thread-safe functions, but NOT reentrant functions>. 
d431 1
a431 1
Especially this means that under B<PTH> more existing third-party libraries
d437 1
a437 1
B<PTH doesn't require any kernel support, but can NOT
d440 2
a441 2
This means that B<PTH> runs on mostly all types of Unix kernels, because the
kernel does not even recognize the B<PTH> threads (because they are
d451 2
a452 2
To better understand the B<PTH> API it is reasonable to first understand the
life cycle of a thread in the B<PTH> threading system. It can be illustrated
d497 1
a497 1
In the following the B<PTH> I<Application Programmers Interface> (API) is
d510 1
a510 1
This initializes the B<PTH> library. It has to be the first B<PTH> API
d518 1
a518 1
This kills the B<PTH> library. It should be the last B<PTH> API function call
d526 1
a526 1
This is a generalized query/control function for the B<PTH> library.  The
d578 1
a578 1
patchlevel=2, etc). For instance PTH version 1.0b1 is encoded as 0x100101.
d587 1
a587 1
Attribute objects are used in B<PTH> for two things: First stand-alone/unbound
d712 1
a712 1
the B<PTH> library.
d760 1
a760 1
a chance to execute, too.  This obviously is the cooperating part of B<PTH>.
d773 1
a773 1
of the non-preemptive nature of B<PTH> it can last longer (when another thread
d800 1
a800 1
``C<pth_exit(PTH_CANCELED)>'' at one of his cancellation points.  In PTH
d833 1
a833 1
prerequisite to use it together with the B<PTH> library.
d844 1
a844 1
B<PTH> supports POSIX style thread cancellation via pth_cancel(3) and the
d874 1
a874 1
B<PTH> has a very flexible event facility which is linked into the scheduler
d902 1
a902 1
the second additional argument. Keep in mind that the B<PTH> scheduler doesn't
d1144 1
a1144 1
in mind that in a non-preemptive threading system like B<PTH> this might sound
d1295 1
a1295 1
because of the non-preemptive scheduling nature of B<PTH>, it can be awakened
d1305 1
a1305 1
non-preemptive scheduling nature of B<PTH>, it can be awakened later, of
d1321 1
a1321 1
This is the PTH thread-related equivalent of POSIX sigprocmask(2) respectively
d1323 1
a1323 1
to sigprocmask(2), because B<PTH> internally just uses sigprocmask(2) here. So
d1391 1
a1391 1
intended to show you the look and feel of B<PTH>.
d1471 1
a1471 1
B<PTH> is very portable because it has only one part which perhaps has to be
d1479 1
a1479 1
switched. Additionally the B<PTH> dispatcher switches also the global Unix
d1484 1
a1484 1
The B<PTH> event manager is mainly select(2) and gettimeofday(2) based, i.e.
d1503 1
a1503 1
B<PTH> uses an explicit API (i.e. for instance you've to use pth_read(3) and
d1505 2
a1506 2
because this way B<PTH> doesn't require any system call wrappers which usually
cannot be provided in a portable way. And portability is one of B<PTH>' major
d1509 1
a1509 13
Additionally B<PTH> currently doesn't provide the standardized POSIX Threading
API ("I<pthread>"), although the B<PTH> API is very close to it.  The reason
for this is that B<PTH>' API is intentionally more flexible. For instance
there is no explicit event mechanism in POSIX threads, etc. But it is
clear that for portability reasons and easy upgrading of applications a
pthread(3) compatible wrapper API for B<PTH> is required sooner or later.
Development for such a wrapper library has already started, but it will
last until B<PTH> version 1.1 before this additional API can be finally
released. Actually this library just maps pth_xxx() functions to
pthread_xxx() functions and tries to emulate the POSIX return value
semantics.

Finally B<PTH> (intentionally) provides no replacements for thread-safe
d1522 1
a1522 1
The B<PTH> library was designed and implemented between February and June 1999
d1528 1
a1528 1
B<PTH> was then implemented in order to combine the I<non-preemptive> approach
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pth_fork,
d1080 60
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=item pid_t B<pth_fork>(void)

This is a variant of fork(2) with the difference that the current thread only
is forked into a separate process, i.e. in the parent process nothing changes
while in the child process all threads are gone except for the scheduler and
the calling thread. When you really want to duplicate all threads in the
current process you should use fork(2) directly. But this is usually not
reasonable.
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@d82 2
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@


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B<PTH> - GNU Portable Threads
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a33 1
PTH PTH_VERSION_STR
@


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@d144 1
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B<PTH> is a portable POSIX/ANSI-C based library for Unix platforms which
d158 4
@


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##  which can be found at http://www.engelschall.com/sw/pth/.
@


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B<PTH> - B<N>on-B<P>reemtive Thread B<S>cheduling Library
@


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This initialized the B<PTH> library. It has to be the first B<PTH> API
@


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@d1467 7
a1476 3

``comp.programming.threads Frequently Asked Questions (F.A.Q.)'',
http://www.lambdacs.com/newsgroup/FAQ.html
@


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@d557 1
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=item int B<pth_version>(void);
@


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@d1 1
a1 1

@


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a1361 2
     attr = pth_attr("ticker", 0, 0, 32*1024, FALSE);
     pth_spawn(&attr, ticker, NULL);
d1372 1
a1372 1
     attr = pth_attr("handler", 0, PTH_FLAG_NOJOIN, 32*1024, NULL);
d1375 1
a1375 1
         pth_spawn(&attr, handler, (void *)sw);
d1464 36
@


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pth_ctrl.
d556 10
@


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C<PTH_CANCEL_DISABLE> and C<PTH_CANCEL_DEFERRED> and
d829 1
a829 1
C<PTH_CANCEL_DEFERRED> and C<PTH_CANCEL_ASYNCHRONOUS>.
@


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This function raises a signal to thread I<tid>. Currently this functionality
of sending a signal to just a particular thread is still not implemented, so
usually this function always returns C<FALSE> with errno set to C<ENOSYS>. But
when I<sig> is 0 POSIX style thread checking is at least possible, i.e.
``C<pth_raise(tid, 0)>'' returns C<TRUE> when thread I<tid> exists in the
B<PTH> system.
@


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@a58 2
pth_sigmask,
pth_sigraise,
d63 1
d131 1
d716 1
a716 9
=item int B<pth_sigmask>(int I<how>, const sigset_t *I<set>, sigset_t *I<oset>)

This is the PTH thread-related equivalent of POSIX sigprocmask(2). The
arguments I<how>, I<set> and I<oset> directly relate to sigprocmask(2),
because B<PTH> internally just uses sigprocmask(2) here. So alternatively you
can also directly call sigprocmask(2), but for consistency reasons you should
use this function pth_sigmask(3).

=item int B<pth_sigraise>(pth_t I<tid>, int I<sig>)
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``C<pth_sigraise(tid, 0)>'' returns C<TRUE> when thread I<tid> exists in the
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The scheduling state of the thread, i.e. either C<pth_state_new>,
C<pth_state_ready>, C<pth_state_waiting>, or C<pth_state_dead>
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pth_attr,
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pth_priority,
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pth_detach,
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pth_time.
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=item pth_attr_t B<pth_attr>(char *I<name>, int I<prio>, unsigned int I<flags>, unsigned int I<stacksize>, void *I<stackaddr>);

This is a constructor for C<pth_attr_t> structures which can be used for the
first argument of pth_spawn(3) when it's not C<PTH_ATTR_NULL>. I<name> is a
string assigned to the thread which is mainly interested for debugging.
I<prio> is the priority of the thread ranging from C<PTH_PRIO_MIN> to
C<PTH_PRIO_MAX>; the default is C<PTH_PRIO_STD>. I<flags> can be either
C<PTH_FLAG_NONE> (no flags) or C<PTH_FLAG_NOJOIN> (indicates that the thread
cannot be joined, i.e. after termination its immediately kicked out of the
system instead of inserted into the dead queue). I<stacksize> is the number of
bytes the stack for the thread is in size. Use lower values than 32768 (32KB)
with care. Finally I<stackaddr> can be a dynamically pre-allocated chunk of
memory (minimum I<stacksize> in length!) which should be used for the stack
(when the thread terminates a free(3) is done). When I<stackaddr> is C<NULL>
(the usual case) then the stack is allocated automatically by the B<PTH>
library.

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=item int B<pth_priority>(pth_t I<tid>, int I<prio>);

This overrides the priority of the thread I<tid> with I<prio>.  The current
priority of a thread can be obtained via ``C<pth_ctrl(PTH_CTRL_GETPRIO,
tid)>''.

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=item int B<pth_detach>(pth_t I<tid>);

This function is used to indicate to the implementation that storage for the
thread I<tid> can be reclaimed when that thread terminates, i.e. it just
detaches the thread by marking it unjoinable (see pth_attr(3) and
C<PTH_FLAG_NOJOIN>).
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pth_equal,
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=item int B<pth_equal>(pth_t I<tid1>, pth_t I<tid2>);

This compares two thread handles and returns C<TRUE> when they are equal, i.e.
when they describe the same thread. For portability reasons do not compare
C<pth_t> variables directly via ``C<==>''.
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=item int B<pth_rwlock_acquire>(pth_rwlock_t *I<rwlock>, int I<op>, pth_event_t I<ev>);
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the locking timeout, etc,
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=item int B<pth_mutex_acquire>(pth_mutex_t *I<mutex>, pth_event_t I<ev>);
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=item void B<pth_event_free>(pth_event_t I<ev>, int I<mode>);
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=item void B<pth_once>(pth_once_t *I<ctrlvar>, void (*I<func>)(void *), void *I<arg>);
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priority of a thread can be obtained via ``C<pth_ctrl(PTH_CTRL_GETPRIO, tid)>''.
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=item void B<pth_nap>(pth_time_t I<naptime>);
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=item B<o> B<reentrant> and B<thread-safe> functions
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the pth_sigwait() call.
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=head2 B<Synchronization>
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=item B<Mutual Exclusion>
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pth_mutex_lock,
pth_mutex_unlock,
pth_mutex_holder.
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=head2 B<Mutual Exclusion>
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locks. Keep in mind that in a non-preemptive threading system like B<PTH> this
might sound unnecessary at the first look, because a thread isn't interrupted
by the system. Actually when you have a critical code section which doesn't
contain any pth_xxx() functions, you don't need any mutex to protect it, of
course. 
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This dynamically initialized a mutex variable of type ``C<pth_mutex_t *>''.
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=item int B<pth_mutex_acquire>(pth_mutex_t *I<mutex>, int I<poll>, pth_event_t I<ev>);
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This acquires a mutex I<mutex>. When I<poll> is C<TRUE> the mutex is only
tried to be acquired. When it is already locked C<FALSE> is returned
immediately. When I<poll> is C<FALSE> and the mutex is already locked the
thread's execution is suspended until the mutex is unlocked again or
additionally the extra events in I<ev> occurred (when I<ev> is not C<NULL>).
Recursive locking is supported, i.e. a thread is allowed to acquire a mutex
more than once before its released. But it then also has be released the same
number of times until the mutex is again lockable by others.
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This decrements the recursion count on I<mutex> and when it is zero it
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=item pth_t B<pth_mutex_holder>(pth_mutex_t *I<mutex>);
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This returns the thread id of the holder of mutex I<mutex>. C<NULL> is
returned when I<mutex> is currently not acquired by a thread.
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pth_mutex_unlock.
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=head2 B<Mutual Exclusion Lock>
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##
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``C<pth_exit(PTH_CANCELED)''.
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performed. When its C<PTH_CANCEL_DEFERED> again the calcellation request is
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C<PTH_CANCEL_DEFERED> and C<PTH_CANCEL_ASYNCHRONOUS>.
C<PTH_CANCEL_ENABLE|PTH_CANCEL_DEFERED> is the default state where
cancellation is possible but only at cancellation points. Use
C<PTH_CANCEL_DISABLE> to complete disable cancellation for a thread and
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=head1 SEE ALSO

pth-config(1), pthread(3).

sigstack(2), sigaltstack(2), sigaction(2), sigemptyset(2), sigaddset(2),
sigprocmask(2).  sigsuspend(2), sigsetjmp(3), siglongjmp(3), setjmp(3),
longjmp(3), select(2), gettimeofday(2).

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("multi-threading") inside server applications.  All threads runs in the same
address space of the server application, but each thread has it's own
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are managed by a priority- and event-based non-preemptive scheduler. The
intention is that this way one can achieve better portability and run-time
performance than with preemptive scheduling.  The event facility allows
threads to wait until various types of events occur, including pending I/O on
filedescriptors, asynchronous signals, elapsed timers, pending I/O on message
ports, thread and process termination, and even customized callback functions.

=head2 Background

When programming server type applications, lots of regular jobs and one-shot
requests have to processed in parallel. To achieve this in an efficient way on
uniprocessor machines the idea of multitasking is implemented by the operation
system which can be used by the applications to spawn multiple instances of
itself. On Unix the kernel implements multitasking in a preemptive and
priority-based way through heavy-weight processes spawned with fork(2).  These
processes do usually I<not> share a common address space. Instead they are
clearly separated from each other and were created by direct cloning a process
address space. 

The drawbacks are obvious: Sharing data is complicated and can usually only
solved in an efficient way through shared memory (which itself is not very
portable). Synchronization is complicated because of the preemptive nature of
the Unix scheduler. The machine resources can be exhausted very quickly when
the server application has to serve too much longer running requests occur
(heavy-weight processes cost memory). Additionally when for each request a
sub-process is spawned to handle it, the server performance is horrible
(heavy-weight processes cost time to spawn). And finally the server
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problems. Lot's of tricks are done in practice to overcome these problems
(ranging from pre-forked sub-process pools to semi-serialized processing,
etc). 

Nevertheless one the most elegant ways to solve the resource and data sharing
problems is to have multiple I<light-weight> threads of execution inside a
single (heavy-weight) process, i.e. to use multithreading. But those
light-weight processes are not supported by all Unix kernels. And even where
kernel threads exists, the thread context switching is usually still too
expensive. So the usual way to solve this is to implement user-land threads
where the process is split into multiple threads of execution by the
application itself and without the knowledge of the kernel and where context
switches can be done faster.
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User-land threads can be implemented in in various way. The two classical
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=item B<1. Matrix-based explicit dispatching between small units of execution:> 
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Here the global procedures of the server application are split into small
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units by calling one function after each other controlled by this matrix.
The treads are created by more than one jump-trail through this matrix and by
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events.  Examples of this is the I<iMatix> B<Libero>/B<SMT> based B<xitami>
web server or the B<Squid> web proxy server. 
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matrix and the scheduling is done explicitly by the application itself) and
that it's very portable (because the matrix is just an ordinary data structure
and functions are a standard feature of ANSI C).

The disadvantage of this approach is that it's complicated to write large
server applications with this approach, because in large applications one
quickly get hundreds of execution units and the control flow inside such an
application is very hard to understand (because it's interrupted by function
borders and one always has to use the global matrix to follow it).
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saves memory it's often nasty because one cannot switch between threads in the
middle of a function. The scheduling borders are function borders.
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=item B<2. Queue-based based implicit scheduling between threads of execution:> 
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synchronization things) doesn't have to care about this.  Examples of this
approach are the various POSIX thread ("pthread") based server applications.
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because the control flow of a thread directly follows a procedure without
forced interrupts through function borders. Additionally the programming is
very similar to the fork(2) approach.
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The disadvantage is that although the general performance is increased
compared to using approaches with heavy-weight processes, it's decreased
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switch costs some overhead even when it's a lot cheaper than a kernel-level
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Finally there is no really portable ANSI C & POSIX based way to implement
preemptive threads yourself. Either the platform already has threads or one has
to hope that some semi-portable package exists for it. And even those
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=head2 The Compromise
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to avoid their bad aspects? That's the general intention of B<PTH>. In detail
this means that B<PTH> implements the easy to program threads of execution but
in a way which doesn't have the portability side-effects of preemptive
scheduling. This means that instead a non-preemptive scheduling is used. 
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To better understand the B<PTH> API its reasonable to first understand the
life cycle of a thread in the B<PTH> system. It can be illustrated with the
following graph:
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       +--> READY---+
       |      ^     |
       |      |     V
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                    |
                    V
                  DEAD
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When a new thread is created it is moved into the B<NEW> queue of the
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want to perform a CPU burst. They are queued  in priority order.  Per
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priority only.  The assigned queue priority for all remaining threads every
time is increased by one to prevent thread starvation.
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thread (there is always just one B<RUNNING> thread, of course). After this
thread yields execution (either explicitly or implicitly by calling a function
which would block) there are three possibilities: Either it has terminated,
then it's moved to the B<DEAD> queue, or it has events on which it wants to
wait, then its moved into the B<WAITING> queue. Else it is assumed it wants to
perform more CPU bursts and enters the B<READY> queue again. 
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occured, its immediately moved to the B<READY> queue, too.
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scheduler and the scheduler invokes a thread. The purpose of the B<DEAD> queue
is to support thread joining. When a thread is marked to be unjoinable, it is
directly kicked out of the system after it terminated. But when its joinable
it enter the B<DEAD> queue.  There is remains until another thread joins it.
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In the following the B<PTH> Application Programmers Interface (API) is
discussed in detail.
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priority of a thread can be obtained via ``pth_ctrl(PTH_CTRL_GETPRIO, tid)''.
a1002 32
=head1 IMPLEMENTATION NOTES

B<PTH> is very portable because it has only one part which perhaps have to be
ported to new platforms (the machine context initialization). But it is
written in a way which works on mostly all Unix platforms which support
sigstack(2) or sigaltstack(2) [see C<pth_mctx.c> for details]. Any other code
is plain POSIX and ANSI C based. 

The context switching is done via POSIX [sig]setjmp(3) and [sig]longjmp(3).
Here all CPU registers, the program counter and the stack pointer are
switched. Additionally the B<PTH> dispatcher switches also the global Unix
C<errno> variable [see C<pth_mctx.c> for details] and the signal mask (either
implicitly via sigsetjmp(3) or in an emulated way via explicit setprocmask(2)
calls).

The B<PTH> event manager is mainly select(2) and gettimeofday(2) based, i.e.
the current time is fetched via gettimeofday(2) once per context switch for
calculations and both the time and all I/O events are implemented via a single
select(2) call [see C<pth_sched.c> for details].

The thread control block management is done via queues without any additional
data structure overhead. For this the queue linkage attributes are part of the
thread control blocks and the queues are actually implemented as rings with a
selected element as the entry point [see C<pth_tcb.h> and C<pth_pqueue.c> for
details].

Most time critical sections (especially the dispatcher and event manager) are
speeded up by inlined functions (implemented as ANSI C macros). Additionally
any debugging code is I<completely> removed from the source when not built
with C<-DPTH_DEBUG> (see C<--enable-debug>), i.e. not only stub functions
remain [see C<pth_debug.h> for details].

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=head1 BUGS
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No real bugs currently known.
d1118 2
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B<PTH> uses an explicit API (i.e. for instance you've to use pth_read() and
cannot just use read()) which might by nasty for some users. The reason is
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Finally B<PTH> (intentionally) provides no replacements for non-reentrant
(e.g. strtok(3) which uses a static internal buffer) or synchronous system
functions (e.g. gethostbyname(3) which doesn't provide an asynchronous mode
where it doesn't block).  When you want to use those functions in your server
application together with threads you've to either link the application
against special third-party libraries (or for reentrant functions possibly
against an existing C<libc_r> of the platform vendor).  For an asynchronous
DNS resolver library use either the new C<libresolv> from B<BIND 8> ( see
ftp://ftp.isc.org/isc/bind/ ) or the forthcoming GNU B<adns> package from Ian
Jackson ( see http://www.gnu.org/software/adns/adns.html ).
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test version of Apache. The concept and API of message ports was borrowed from
AmigaOS' B<Exec>. The concept and idea for the flexible event mechanism came
from I<Paul Vixie>'s B<eventlib> (part of B<BIND8>).
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This is a variant of the POSIX waitpid(2) function. It suspends suspends the
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performance than with preemptive scheduling.  The event facility allows threads
to wait until various types of events occur, including pending I/O on
filedescriptors, elapsed timers, pending I/O on message ports, thread and
process termination, and even customized callback functions.
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individual run-time stack and program-counter.
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=item C<PTH_EVENT_SIG>
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This is a signal event. The additional argument has to be a signal number
(``C<SIG>I<name>''). This event wait until the signal is pending. Keep in mind
that the B<PTH> scheduler doesn't block signals itself.  So when you want to
wait for a signal with this event you've to block it via sigprocmask(2) or it
will be delivered without your notice.  Example: ``C<pth_event(PTH_EVENT_SIG,
SIGUSR1)>''.
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returns this new reached event.
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pth_event
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B<PTH> is a maximum portable POSIX/ANSI-C based library for Unix platforms
which provides non-preemptive scheduling for multiple threads of execution
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with care.
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This overrides the priority of the thread I<thread> with I<prio>.  The current
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the various pth_event_xxx() functions). Its modeled like select(2), i.e. one
gives this function one or more events (in the event ring specified by
I<ev>) on which the current thread wants to wait.  The scheduler awakes the
thread when one ore more of them occurred after tagging them as occured. The
I<ev> argument is a I<pointer> to an event ring which isn't changed except for
the tagging. pth_wait(3) returns the number of occured events and the
application can use pth_event_occurred(3) to test which events occured.
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This is a constructor for a pth_time_t structure which is a convenient
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This creates a new event ring consisting of a single event.
Its type is specified by I<spec>. ???MORE DETAILS???
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and returns I<ev>. The end of the argument list has to be a C<NULL> argument.
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This isolates the event I<ev> from possibly appended
events in the event ring.
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This walks to the next or previews event in the event ring I<ev> and
returns this event.
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This checks whether the event I<ev> occurred.

=item void B<pth_event_free>(pth_event_t I<ev>, int I<all>);

This deallocates the event I<ev> or all events appended to it.
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ported to new platforms (the machine context initialization). But its written
in a way which works on mostly all Unix platforms which support sigstack(2) or
sigaltstack(2) [see C<pth_mctx.c> for details]. Any other code is plain POSIX
and ANSI C based. 

The context switching is done via POSIX setjmp(3) and longjmp(3).  Here all
CPU registers, the program counter and the stack pointer are switched.
Additionally the B<PTH> dispatcher switches also the global Unix C<errno>
variable [see C<pth_mctx.c> for details].
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the current time is fetched via gettimeofday(2) on every context switch for
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data structure overhead. For this the queue linkage variables are part of the
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     attr = pth_attr("handler", 0, 0, 32*1024, FALSE);
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Additionally B<PTH> still lacks support for per-thread signal handling.

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sigstack(2), sigaltstack(2), sigaction(2), sigemptyset(2), sigaddset(2), sigprocmask(2).
setjmp(3), longjmp(3), select(2), gettimeofday(2).
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The B<PTH> library was designed and implemented between February and May 1999
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I<Lars Eilebrecht> and I<Ralph Babel> related to an experimental (matrix based)
non-preemptive C++ scheduler class written by I<Peter Simons>. 
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##  License along with this library; if not, write to the Free
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=item pth_attr_t B<pth_attr>(char *I<name>, int I<prio>, unsigned int I<flags>, unsigned int I<stacksize>);
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=item int B<pth_wait>(pth_event_t *I<ev_waiting>, pth_event_t *I<ev_occurred>);
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the various pth_event_xxx() functions). Its modeled like select(2), i.e.  one
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I<ev_waiting>) on which the current thread wants to wait.  The scheduler
awakes the thread when one ore more of them occurred after moving them from
I<ev_waiting> to I<ev_occurred> (the second event ring). Both arguments are
I<pointers> to event rings. I<ev_occurred> is usually just a pointer to a
C<pth_event_t> variable (which needs not to be initialized but can be).  

When I<ev_occurred> is specified as C<NULL>, the scheduler doesn't move the
occurred events out of I<ev_waiting>, i.e. the application then has to use
pth_event_occurred(3) explicitly on all events in I<ev_waiting> to find out
which one has occurred, but this way it can reuse the I<ev_waiting> event ring.
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and returns I<ev>.
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DNS resolver library use either the new C<libresolv> from B<BIND 8> (see
ftp://ftp.isc.org/isc/bind/) or the forthcoming GNU B<adns> package from Ian
Jackson (see http://www.gnu.org/software/adns/adns.html).
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I<Lars Eilebrecht> and I<Ralf Babel> related to an experimental (matrix based)
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threading library (B<rsthread>) written by I<Robert S. Tau> for an ancient
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Finally N<PTH> (intentionally) provides no replacements for non-reentrant
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When a new thread is created it is moved into the NEW queue of the scheduler.
On the next dispatching the scheduler picks it up from there and moves it to
the READY queue. This is a queue containing all threads which want to perform
a CPU burst. They are queued  in priority order.  Per dispatching step, the
scheduler always removes the thread with the highest priority only.  The
assigned queue priority for all remaining threads every time is increased by
one to prevent thread starvation.
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The thread which was removed from the READY queue is the new RUNNING thread
(there is always just one RUNNING thread, of course). After this thread yields
execution (either explicitly or implicitly by calling a function which would
block) there are three possibilities: Either it has terminated, then it's
moved to the DEAD queue, or it has events on which it wants to wait, then its
moved into the WAITING queue. Else it is assumed it wants to perform more CPU
bursts and enters the READY queue again. 
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Before the next thread is taken out of the READY queue, the WAITING queue is
checked for pending events. When one or more events of a thread occured, its
immediately moved to the READY queue, too.
d275 1
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The purpose of the NEW queue has to do with the fact that a thread never
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scheduler and the scheduler invokes a thread. The purpose of the DEAD queue is
to support thread joining. When a thread is marked to be unjoinable, it is
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it enter the DEAD queue.  There is remains until another thread joins it.
@


1.18
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@
text
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@


1.17
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text
@d806 11
@


1.16
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sigaltstack(2) [see C<pth_mctx.c for details]. Any other code is plain POSIX
@


1.15
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@
text
@d681 30
@


1.14
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@
text
@d400 1
a400 1
=item int B<pth_wait>(pth_event_t *I<ev_waiting>, pth_event_t *I<ev_occured>);
d407 2
a408 2
I<ev_waiting> to I<ev_occured> (the second event ring). Both arguments are
I<pointers> to event rings. I<ev_occured> is usually just a pointer to a
d411 1
a411 1
When I<ev_occured> is specified as C<NULL>, the scheduler doesn't move the
d482 1
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=item int B<pth_event_occured>(pth_event_t I<ev>);
@


1.13
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@
text
@d70 1
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pth_event_occured,
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leight-weight processes are not supported by all Unix kernels. And even where
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switching between these jump-trails controlled by corresponding occured
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quickly get hundrets of execution units and the control flow inside such an
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a254 1
begin of the main() function of the application. This implicity spawns the
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complete processo and not just the current thread.
d350 1
a350 1
This is a convienience function which uses a control variable of type
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nor that the threas is awakened exactly after I<naptime> has elapsed. It's
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a394 1
of the non-preemtive nature of B<PTH> it can last longer (when another thread
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awakes the thread when one ore more of them occured after moving them from
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occured events out of I<ev_waiting>, i.e. the application then has to use
pth_event_occured(3) explicitly on all events in I<ev_waiting> to find out
which one has occured, but this way it can reuse the I<ev_waiting> event ring.
d449 1
a449 1
This is a constructor for a pth_time_t structure which is a convinient
d484 1
a484 1
This checks whether the event I<ev> occured.
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a502 1
can specifiy a destructor function which is called on the current threads
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a573 1
This is equal to pth_write(3) (see below), but has an addtional event argument
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a581 1
This is equal to pth_read(3) (see below), but has an addtional event argument
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a589 1
This is equal to pth_readline(3) (see below), but has an addtional event
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a671 1
This is a convienience function which is based on pth_read(3).  It reads bytes
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occured or I<buflen> is reached. It internally uses thread-local buffering to
@


1.12
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@
text
@d252 5
a256 2
This initialized the B<PTH> library. It has to be the first pth_xxx() call
made by an application.
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a311 1
...
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a313 5
This returns a floating point value describing the exponential averaged load
of the scheduler. The load is a function from the number of threads in the
ready queue of the schedulers dispatching unit. So a load around 1.0 means
there is only one ready thread. A higher load means there a more threads ready
who want to do CPU bursts. The average load value is adjusted once per second.
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The following functions control the threading itself.
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=item pth_attr_t B<pth_attr>(char *I<name>, int I<prio>, unsigned int I<flags>, unsigned int I<stacksize>, int I<joinable>);
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This spawns a new thread with the attributes given in I<attr> with the start
point at routine I<entry>. This entry routine is called as I<entry>(I<arg>)
inside the new thread. When I<entry> returns an implicit pth_exit(NULL) is
done.
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=item void B<pth_once>(pth_once_t *I<oncectrl>, void (*I<constructor>)(void *), void *I<arg>);
d366 3
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=item pth_t B<pth_self>(void);
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=item int B<pth_equal>(pth_t I<thread1>, pth_t I<thread2>);
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=item void B<pth_priority>(pth_t I<thread>, int I<prio>);
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a423 1
=item int B<pth_wait>(pth_event_t *I<ev_pending>, pth_event_t *I<ev_occured>);
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=item int B<pth_join>(pth_t I<thread>, void **I<value>);
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a432 1
=item void B<pth_exit>(void *I<value>);
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d444 3
d449 3
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d464 3
d469 3
d474 3
d479 3
d484 2
d488 1
d494 3
d501 4
d507 2
d511 2
d515 2
d521 3
d528 4
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d539 3
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d548 2
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d581 6
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This is a variant of the 4.2BSD accept(2) function. It accepts a connection on
a socket by extracting the first connection request on the queue of pending
connections, creating a new socket with the same properties of I<s> and
allocates a new file descriptor for the socket (which is returned).  For more
details about the arguments and return code semantics see accept(2).
d663 6
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a679 1

@


1.11
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@
text
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This is a variant of 4.3BSD's usleep(3) function. It suspends the current
threads execution until I<usec> microsecond (= I<usec> * 1/1000000s) elapsed.
The thread is guarrantied to not awakened before this time, but because of the
non-preemptive scheduling nature of B<PTH>, it can be awakened a lot later.
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@


1.10
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@
text
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##  This file is part of PTH, a non-preemtive thread scheduling library
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which provides non-preemtive scheduling for multiple threads of execution
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are managed by a priority- and event-based non-preemtive scheduler. The
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performance than with preemtive scheduling.  The event facility allows threads
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itself. On Unix the kernel implements multitasking in a preemtive and
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portable). Synchronization is complicated because of the preemtive nature of
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still interrupted - even in the middle of a function.  Actually in a preemtive
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compared to the matrix-approach above. Because the implicit preemtive
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context switch) than the explicit cooperative/non-preemtive scheduling.
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preemtive threads yourself. Either the platform already has threads or one has
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from synchronization and portability problems caused by its preemtive nature.
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in a way which doesn't have the portability side-effects of preemtive
scheduling. This means that instead a non-preemtive scheduling is used. 
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a519 1
by I<Ralf S. Engelschall> after evaluating various (mostly preemtive) thread
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non-preemtive C++ scheduler class written by I<Peter Simons>. 
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B<PTH> was then implemented in order to combine the I<non-preemtive> approach
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So the essential idea for the non-preemtive approach was taken over from
@


1.9
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@


1.8
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@
text
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pth_stat,
pth_load.
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a258 1
=item unsigned int B<pth_stat>(int I<type>);
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a264 1
=item float B<pth_load>(void);
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a467 1
     sar.sin_family      = AF_INET;
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a469 1
     sar.sin_port        = htons(port);
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d496 4
a499 1
pth-config(1), pthread(3), fork(2).
d503 4
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The B<PTH> library was designed and implemented between February and May
1999 by I<Ralf S. Engelschall> after evaluating various (mostly preemtive)
thread libraries and intensive discussions with I<Peter Simons>, I<Martin
Kraemer> and I<Lars Eilebrecht> related to an experimental (matrix based)
d512 9
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programming). Some code inspiration also came from an old (never publically
released) threading library written by I<Robert S. Tau>.  Additionally the
concept and API of message ports was borrowed from AmigaOS' I<Exec> after,
while the idea for the event mechanism itself came from I<Paul Vixie>'s
I<eventlib>.

So, the essential idea for the non-preemtive approach was take over from
I<Peter Simons> scheduler.  The priority based scheduling algorithm was
contributed by I<Martin Kraemer>.  initial. Some hard-core for the machine
context switching was borrowed from I<Robert S. Tau>'s threading library.  The
implementation of B<PTH> itself was done by I<Ralf S. Engelschall>.
@


1.7
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@
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@d43 2
a44 1
pth_stat.
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B<PTH> is a POSIX/ANSI-C based library for Unix platforms which provides
non-preemtive scheduling for multiple threads of execution ("multi-threading")
inside server applications.  All threads runs in the same address space of the
server application, but each thread has it's own individual run-time stack and
program-counter.
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synchronization things) doesn't have to care about this.
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in a way which doesn't have the side-effects of preemtive scheduling. This
means that instead a non-preemtive scheduling is used. 
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a255 1
...
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a467 1
...
@


1.6
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inside high-performance server applications.  All threads runs in the same
address space of the server application, but each thread has it's own
individual run-time stack and program-counter.
@


1.5
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@
text
@a0 2
## ====================================================================
## Copyright (c) 1999 Ralf S. Engelschall. All rights reserved.
d2 6
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## Redistribution and use in source and binary forms, with or without
## modification, are permitted provided that the following conditions
## are met:
##
## 1. Redistributions of source code must retain the above copyright
##    notice, this list of conditions and the following disclaimer. 
##
## 2. Redistributions in binary form must reproduce the above copyright
##    notice, this list of conditions and the following disclaimer in
##    the documentation and/or other materials provided with the
##    distribution.
##
## 3. All advertising materials mentioning features or use of this
##    software must display the following acknowledgment:
##    "This product includes software developed by
##     Ralf S. Engelschall <rse@@engelschall.com>."
##
## 4. Redistributions of any form whatsoever must retain the following
##    acknowledgment:
##    "This product includes software developed by
##     Ralf S. Engelschall <rse@@engelschall.com>."
##
## THIS SOFTWARE IS PROVIDED BY RALF S. ENGELSCHALL ``AS IS'' AND ANY
## EXPRESSED OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
## IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
## PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL RALF S. ENGELSCHALL OR
## ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
## SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
## NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
## LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
## HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
## STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
## ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
## OF THE POSSIBILITY OF SUCH DAMAGE.
## ====================================================================

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## pth.pod -- PTH manpage
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B<PTH> - B<N>on-B<P>reemtive B<S>cheduling Library
@


1.4
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B<PTH> - Non-Preemtive Scheduling Library
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B<PTH> is a POSIX/ANSI-C based library for Unix platforms which provides
non-preemtive scheduling for multiple threads of execution
("I<multi-threading>") inside high-performance server applications.  All
threads runs in the same address space of the server application, but each
thread has it's own individual run-time stack and program-counter. The API is
very similar to the POSIX threads API ("I<pthreads>"), i.e. one can spawn and
join threads.  

But the thread scheduling itself is done in a cooperative instead of the usual
preemtive way.  The threads are managed by a priority- and event-based
non-preemtive scheduler. The intention is to achieve this way better
portability and run-time performance.  The event facility allows threads to
wait until various types of events occur, including filedescriptor I/O,
elapsed timers, raised signals, message port I/O, thread and process
termination, etc.
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clearly separated from each other. 
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the Unix scheduler.  The machine resources can be exhausted very quickly when
the server application has to serve too much one-shot requests at once
d165 2
a166 1
(ranging from pre-forked sub-process pools to semi-serialized processing). 
d168 9
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Nevertheless the most elegant way to solve the resource and data sharing
problems would be to have multiple I<light-weight> threads of execution inside
a (heavy-weight) process, i.e. to use multithreading. But those leight-weight
processes are not supported by all Unix kernels. So the usual way to solve
this is to implement user-land threads where the process is split into
multiple threads of execution by the application itself and without the
knowledge of the kernel.
d181 1
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approaches exists:
d185 1
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=item B<1.>
d187 3
a189 4
B<matrix-based explicit dispatching between small units of execution:> Here the
global procedures of the server application are split into small execution
units (each has to run maximal a few milliseconds) and those units are
implemented by separate program functions. Then a global matrix is created
d193 4
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Examples of this is the iMatix Libero/SMT based xitami server or the Squid web
proxy server. 
d199 4
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possible (because one can fine-tune the threads of execution because the
scheduling is done explicitly by the application itself) and that it's very
portable (because the matrix is just an ordinary data structure and functions
are a standard feature of ANSI C).
d209 14
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=item B<2.>

B<queue-based based implicit scheduling between threads of execution:> Here
the idea is that one programs as with fork(2)'ed processes, i.e.  one spawns a
thread of execution and this runs from the begin to the end without an
interrupted control flow. But the execution control is interrupted, of course.
Actually in a preemtive way similar to what the kernel does for the
heavy-weight processes, i.e. every few milliseconds the scheduler switches
between the threads of execution. But the thread itself doesn't recognize this
and usually (except for synchronization things) doesn't have to care about
this.
d226 2
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forced interrupts. Additionally the programming is very similar to the fork(2)
approach.
d235 1
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Additionally one more side-effect of this preemtive approach is that one
large procedures via implicit preemtion (e.g. POSIX threads).  And finally
there is no really portable ANSI C & POSIX based way to implement
d247 1
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=head1 The Compromise
d250 1
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to avoid their bad aspects? That's The general intention of B<PTH>. In detail
d252 4
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in a way which doesn't have the side-effects. This means that instead of
preemtive scheduling a non-preemtive scheduling is used. 
d257 4
a260 1
=head1 FUNCTIONS
d264 28
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The B<PTH> library was designed between February 1999 and May 1999 by I<Ralf
S.  Engelschall> after evaluating various (mostly preemtive) thread libraries
and intensive discussions with I<Peter Simons>, I<Martin Kraemer> and I<Lars
Eilebrecht> related to an experimental (matrix based) non-preemtive C++
scheduler class written by I<Peter Simons>. 
@


1.3
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@
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programming). Additional code inspiration came from an old (never publically
released) threading library written by I<Robert S. Tau>. 
d213 1
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context switching was borrowed from I<Robert S. Tau>'s threading library. The
@


1.2
log
@*** empty log message ***
@
text
@d195 5
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The B<PTH> library was written between February 1999 and May 1999 by Ralf S.
Engelschall. It was inspired by an experimental (matrix based) non-preemtive
C++ scheduler class written by Peter Simons and a thread-package by Robert S.
Tau. Ralf S. Engelschall combined the non-preemtive approach with the popular
idea of threads of executions one can found in POSIX thread libraries after
receiving excellent hints from Peter Simons, Martin Kraemer and Lars
Eilebrecht. 
d201 11
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The non-preemtive nature was takeb over from Peter Simons. The priority based
scheduling algorithm was contributed by Martin Kraemer.  So the original
intention of B<PTH> was to combine the speed and simplicity of matrix based
dispatching libraries with the programming idea of multiple threads of
execution from the preemtive POSIX threading libraries.
@


1.1
log
@Initial revision
@
text
@d48 1
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B<pth> - Non-Preemtive Scheduler
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...
@


1.1.1.1
log
@Import of PTH into CVS
@
text
@@