1 | /* POSIX-based operating system interface for GNU Make.
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2 | Copyright (C) 2016 Free Software Foundation, Inc.
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3 | This file is part of GNU Make.
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4 |
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5 | GNU Make is free software; you can redistribute it and/or modify it under the
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6 | terms of the GNU General Public License as published by the Free Software
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7 | Foundation; either version 3 of the License, or (at your option) any later
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8 | version.
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9 |
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10 | GNU Make is distributed in the hope that it will be useful, but WITHOUT ANY
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11 | WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
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12 | A PARTICULAR PURPOSE. See the GNU General Public License for more details.
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13 |
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14 | You should have received a copy of the GNU General Public License along with
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15 | this program. If not, see <http://www.gnu.org/licenses/>. */
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16 |
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17 | #include "makeint.h"
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18 |
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19 | #include <stdio.h>
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20 |
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21 | #ifdef HAVE_FCNTL_H
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22 | # include <fcntl.h>
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23 | #endif
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24 | #if defined(HAVE_PSELECT) && defined(HAVE_SYS_SELECT_H)
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25 | # include <sys/select.h>
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26 | #endif
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27 |
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28 | #include "debug.h"
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29 | #include "job.h"
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30 | #include "os.h"
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31 |
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32 | #ifdef MAKE_JOBSERVER
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33 |
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34 | /* This section provides OS-specific functions to support the jobserver. */
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35 |
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36 | /* These track the state of the jobserver pipe. Passed to child instances. */
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37 | static int job_fds[2] = { -1, -1 };
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38 |
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39 | /* Used to signal read() that a SIGCHLD happened. Always CLOEXEC.
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40 | If we use pselect() this will never be created and always -1.
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41 | */
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42 | static int job_rfd = -1;
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43 |
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44 | /* Token written to the pipe (could be any character...) */
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45 | static char token = '+';
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46 |
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47 | static int
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48 | make_job_rfd (void)
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49 | {
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50 | #ifdef HAVE_PSELECT
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51 | /* Pretend we succeeded. */
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52 | return 0;
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53 | #else
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54 | EINTRLOOP (job_rfd, dup (job_fds[0]));
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55 | if (job_rfd >= 0)
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56 | CLOSE_ON_EXEC (job_rfd);
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57 |
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58 | return job_rfd;
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59 | #endif
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60 | }
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61 |
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62 | unsigned int
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63 | jobserver_setup (int slots)
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64 | {
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65 | int r;
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66 |
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67 | EINTRLOOP (r, pipe (job_fds));
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68 | if (r < 0)
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69 | pfatal_with_name (_("creating jobs pipe"));
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70 |
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71 | if (make_job_rfd () < 0)
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72 | pfatal_with_name (_("duping jobs pipe"));
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73 |
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74 | while (slots--)
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75 | {
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76 | EINTRLOOP (r, write (job_fds[1], &token, 1));
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77 | if (r != 1)
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78 | pfatal_with_name (_("init jobserver pipe"));
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79 | }
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80 |
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81 | return 1;
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82 | }
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83 |
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84 | unsigned int
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85 | jobserver_parse_auth (const char *auth)
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86 | {
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87 | /* Given the command-line parameter, parse it. */
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88 | if (sscanf (auth, "%d,%d", &job_fds[0], &job_fds[1]) != 2)
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89 | OS (fatal, NILF,
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90 | _("internal error: invalid --jobserver-auth string '%s'"), auth);
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91 |
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92 | DB (DB_JOBS,
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93 | (_("Jobserver client (fds %d,%d)\n"), job_fds[0], job_fds[1]));
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94 |
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95 | #ifdef HAVE_FCNTL_H
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96 | # define FD_OK(_f) (fcntl ((_f), F_GETFD) != -1)
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97 | #else
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98 | # define FD_OK(_f) 1
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99 | #endif
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100 |
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101 | /* Make sure our pipeline is valid, and (possibly) create a duplicate pipe,
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102 | that will be closed in the SIGCHLD handler. If this fails with EBADF,
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103 | the parent has closed the pipe on us because it didn't think we were a
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104 | submake. If so, warn and default to -j1. */
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105 |
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106 | if (!FD_OK (job_fds[0]) || !FD_OK (job_fds[1]) || make_job_rfd () < 0)
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107 | {
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108 | if (errno != EBADF)
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109 | pfatal_with_name (_("jobserver pipeline"));
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110 |
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111 | job_fds[0] = job_fds[1] = -1;
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112 |
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113 | return 0;
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114 | }
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115 |
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116 | return 1;
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117 | }
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118 |
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119 | char *
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120 | jobserver_get_auth (void)
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121 | {
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122 | char *auth = xmalloc ((INTSTR_LENGTH * 2) + 2);
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123 | sprintf (auth, "%d,%d", job_fds[0], job_fds[1]);
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124 | return auth;
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125 | }
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126 |
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127 | unsigned int
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128 | jobserver_enabled (void)
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129 | {
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130 | return job_fds[0] >= 0;
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131 | }
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132 |
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133 | void
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134 | jobserver_clear (void)
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135 | {
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136 | if (job_fds[0] >= 0)
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137 | close (job_fds[0]);
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138 | if (job_fds[1] >= 0)
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139 | close (job_fds[1]);
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140 | if (job_rfd >= 0)
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141 | close (job_rfd);
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142 |
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143 | job_fds[0] = job_fds[1] = job_rfd = -1;
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144 | }
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145 |
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146 | void
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147 | jobserver_release (int is_fatal)
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148 | {
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149 | int r;
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150 | EINTRLOOP (r, write (job_fds[1], &token, 1));
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151 | if (r != 1)
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152 | {
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153 | if (is_fatal)
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154 | pfatal_with_name (_("write jobserver"));
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155 | perror_with_name ("write", "");
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156 | }
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157 | }
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158 |
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159 | unsigned int
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160 | jobserver_acquire_all (void)
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161 | {
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162 | unsigned int tokens = 0;
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163 |
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164 | /* Close the write side, so the read() won't hang. */
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165 | close (job_fds[1]);
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166 | job_fds[1] = -1;
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167 |
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168 | while (1)
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169 | {
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170 | char intake;
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171 | int r;
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172 | EINTRLOOP (r, read (job_fds[0], &intake, 1));
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173 | if (r != 1)
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174 | return tokens;
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175 | ++tokens;
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176 | }
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177 | }
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178 |
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179 | /* Prepare the jobserver to start a child process. */
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180 | void
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181 | jobserver_pre_child (int recursive)
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182 | {
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183 | /* If it's not a recursive make, avoid polutting the jobserver pipes. */
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184 | if (!recursive && job_fds[0] >= 0)
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185 | {
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186 | CLOSE_ON_EXEC (job_fds[0]);
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187 | CLOSE_ON_EXEC (job_fds[1]);
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188 | }
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189 | }
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190 |
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191 | void
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192 | jobserver_post_child (int recursive)
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193 | {
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194 | #if defined(F_GETFD) && defined(F_SETFD)
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195 | if (!recursive && job_fds[0] >= 0)
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196 | {
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197 | unsigned int i;
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198 | for (i = 0; i < 2; ++i)
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199 | {
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200 | int flags;
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201 | EINTRLOOP (flags, fcntl (job_fds[i], F_GETFD));
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202 | if (flags >= 0)
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203 | {
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204 | int r;
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205 | EINTRLOOP (r, fcntl (job_fds[i], F_SETFD, flags & ~FD_CLOEXEC));
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206 | }
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207 | }
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208 | }
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209 | #endif
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210 | }
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211 |
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212 | void
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213 | jobserver_signal (void)
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214 | {
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215 | if (job_rfd >= 0)
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216 | {
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217 | close (job_rfd);
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218 | job_rfd = -1;
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219 | }
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220 | }
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221 |
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222 | void
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223 | jobserver_pre_acquire (void)
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224 | {
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225 | /* Make sure we have a dup'd FD. */
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226 | if (job_rfd < 0 && job_fds[0] >= 0 && make_job_rfd () < 0)
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227 | pfatal_with_name (_("duping jobs pipe"));
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228 | }
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229 |
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230 | #ifdef HAVE_PSELECT
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231 |
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232 | /* Use pselect() to atomically wait for both a signal and a file descriptor.
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233 | It also provides a timeout facility so we don't need to use SIGALRM.
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234 |
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235 | This method relies on the fact that SIGCHLD will be blocked everywhere,
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236 | and only unblocked (atomically) within the pselect() call, so we can
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237 | never miss a SIGCHLD.
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238 | */
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239 | unsigned int
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240 | jobserver_acquire (int timeout)
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241 | {
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242 | sigset_t empty;
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243 | fd_set readfds;
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244 | struct timespec spec;
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245 | struct timespec *specp = NULL;
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246 | int r;
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247 | char intake;
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248 |
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249 | sigemptyset (&empty);
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250 |
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251 | FD_ZERO (&readfds);
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252 | FD_SET (job_fds[0], &readfds);
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253 |
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254 | if (timeout)
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255 | {
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256 | /* Alarm after one second (is this too granular?) */
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257 | spec.tv_sec = 1;
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258 | spec.tv_nsec = 0;
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259 | specp = &spec;
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260 | }
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261 |
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262 | r = pselect (job_fds[0]+1, &readfds, NULL, NULL, specp, &empty);
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263 |
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264 | if (r == -1)
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265 | {
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266 | /* Better be SIGCHLD. */
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267 | if (errno != EINTR)
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268 | pfatal_with_name (_("pselect jobs pipe"));
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269 | return 0;
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270 | }
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271 |
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272 | if (r == 0)
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273 | /* Timeout. */
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274 | return 0;
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275 |
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276 | /* The read FD is ready: read it! */
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277 | EINTRLOOP (r, read (job_fds[0], &intake, 1));
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278 | if (r < 0)
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279 | pfatal_with_name (_("read jobs pipe"));
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280 |
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281 | /* What does it mean if read() returns 0? It shouldn't happen because only
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282 | the master make can reap all the tokens and close the write side...?? */
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283 | return r > 0;
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284 | }
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285 |
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286 | #else
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287 |
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288 | /* This method uses a "traditional" UNIX model for waiting on both a signal
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289 | and a file descriptor. However, it's complex and since we have a SIGCHLD
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290 | handler installed we need to check ALL system calls for EINTR: painful!
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291 |
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292 | Read a token. As long as there's no token available we'll block. We
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293 | enable interruptible system calls before the read(2) so that if we get a
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294 | SIGCHLD while we're waiting, we'll return with EINTR and we can process the
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295 | death(s) and return tokens to the free pool.
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296 |
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297 | Once we return from the read, we immediately reinstate restartable system
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298 | calls. This allows us to not worry about checking for EINTR on all the
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299 | other system calls in the program.
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300 |
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301 | There is one other twist: there is a span between the time reap_children()
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302 | does its last check for dead children and the time the read(2) call is
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303 | entered, below, where if a child dies we won't notice. This is extremely
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304 | serious as it could cause us to deadlock, given the right set of events.
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305 |
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306 | To avoid this, we do the following: before we reap_children(), we dup(2)
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307 | the read FD on the jobserver pipe. The read(2) call below uses that new
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308 | FD. In the signal handler, we close that FD. That way, if a child dies
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309 | during the section mentioned above, the read(2) will be invoked with an
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310 | invalid FD and will return immediately with EBADF. */
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311 |
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312 | static RETSIGTYPE
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313 | job_noop (int sig UNUSED)
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314 | {
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315 | }
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316 |
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317 | /* Set the child handler action flags to FLAGS. */
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318 | static void
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319 | set_child_handler_action_flags (int set_handler, int set_alarm)
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320 | {
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321 | struct sigaction sa;
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322 |
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323 | #ifdef __EMX__
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324 | /* The child handler must be turned off here. */
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325 | signal (SIGCHLD, SIG_DFL);
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326 | #endif
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327 |
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328 | memset (&sa, '\0', sizeof sa);
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329 | sa.sa_handler = child_handler;
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330 | sa.sa_flags = set_handler ? 0 : SA_RESTART;
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331 |
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332 | #if defined SIGCHLD
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333 | if (sigaction (SIGCHLD, &sa, NULL) < 0)
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334 | pfatal_with_name ("sigaction: SIGCHLD");
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335 | #endif
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336 |
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337 | #if defined SIGCLD && SIGCLD != SIGCHLD
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338 | if (sigaction (SIGCLD, &sa, NULL) < 0)
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339 | pfatal_with_name ("sigaction: SIGCLD");
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340 | #endif
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341 |
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342 | #if defined SIGALRM
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343 | if (set_alarm)
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344 | {
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345 | /* If we're about to enter the read(), set an alarm to wake up in a
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346 | second so we can check if the load has dropped and we can start more
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347 | work. On the way out, turn off the alarm and set SIG_DFL. */
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348 | if (set_handler)
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349 | {
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350 | sa.sa_handler = job_noop;
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351 | sa.sa_flags = 0;
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352 | if (sigaction (SIGALRM, &sa, NULL) < 0)
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353 | pfatal_with_name ("sigaction: SIGALRM");
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354 | alarm (1);
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355 | }
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356 | else
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357 | {
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358 | alarm (0);
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359 | sa.sa_handler = SIG_DFL;
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360 | sa.sa_flags = 0;
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361 | if (sigaction (SIGALRM, &sa, NULL) < 0)
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362 | pfatal_with_name ("sigaction: SIGALRM");
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363 | }
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364 | }
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365 | #endif
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366 | }
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367 |
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368 | unsigned int
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369 | jobserver_acquire (int timeout)
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370 | {
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371 | char intake;
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372 | int got_token;
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373 | int saved_errno;
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374 |
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375 | /* Set interruptible system calls, and read() for a job token. */
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376 | set_child_handler_action_flags (1, timeout);
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377 |
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378 | EINTRLOOP (got_token, read (job_rfd, &intake, 1));
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379 | saved_errno = errno;
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380 |
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381 | set_child_handler_action_flags (0, timeout);
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382 |
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383 | if (got_token == 1)
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384 | return 1;
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385 |
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386 | /* If the error _wasn't_ expected (EINTR or EBADF), fatal. Otherwise,
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387 | go back and reap_children(), and try again. */
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388 | errno = saved_errno;
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389 |
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390 | if (errno != EINTR && errno != EBADF)
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391 | pfatal_with_name (_("read jobs pipe"));
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392 |
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393 | if (errno == EBADF)
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394 | DB (DB_JOBS, ("Read returned EBADF.\n"));
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395 |
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396 | return 0;
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397 | }
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398 |
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399 | #endif
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400 |
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401 | #endif /* MAKE_JOBSERVER */
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402 |
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403 | /* Create a "bad" file descriptor for stdin when parallel jobs are run. */
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404 | int
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405 | get_bad_stdin (void)
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406 | {
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407 | static int bad_stdin = -1;
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408 |
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409 | /* Set up a bad standard input that reads from a broken pipe. */
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410 |
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411 | if (bad_stdin == -1)
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412 | {
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413 | /* Make a file descriptor that is the read end of a broken pipe.
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414 | This will be used for some children's standard inputs. */
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415 | int pd[2];
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416 | if (pipe (pd) == 0)
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417 | {
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418 | /* Close the write side. */
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419 | (void) close (pd[1]);
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420 | /* Save the read side. */
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421 | bad_stdin = pd[0];
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422 |
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423 | /* Set the descriptor to close on exec, so it does not litter any
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424 | child's descriptor table. When it is dup2'd onto descriptor 0,
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425 | that descriptor will not close on exec. */
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426 | CLOSE_ON_EXEC (bad_stdin);
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427 | }
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428 | }
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429 |
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430 | return bad_stdin;
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431 | }
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