lib/wait-process.c

   1 /* Waiting for a subprocess to finish.
   2    Copyright (C) 2001-2003, 2005-2020 Free Software Foundation, Inc.
   3    Written by Bruno Haible <haible@clisp.cons.org>, 2001.
   4
   5    This program is free software: you can redistribute it and/or modify
   6    it under the terms of the GNU General Public License as published by
   7    the Free Software Foundation; either version 3 of the License, or
   8    (at your option) any later version.
   9
  10    This program is distributed in the hope that it will be useful,
  11    but WITHOUT ANY WARRANTY; without even the implied warranty of
  12    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  13    GNU General Public License for more details.
  14
  15    You should have received a copy of the GNU General Public License
  16    along with this program.  If not, see <https://www.gnu.org/licenses/>.  */
  17
  18
  19 #include <config.h>
  20
  21 /* Specification.  */
  22 #include "wait-process.h"
  23
  24 #include <errno.h>
  25 #include <stdlib.h>
  26 #include <string.h>
  27 #include <signal.h>
  28
  29 #include <sys/types.h>
  30 #include <sys/wait.h>
  31
  32 #include "error.h"
  33 #include "fatal-signal.h"
  34 #include "xalloc.h"
  35 #include "gettext.h"
  36
  37 #define _(str) gettext (str)
  38
  39 #define SIZEOF(a) (sizeof(a) / sizeof(a[0]))
  40
  41
  42 #if defined _WIN32 && ! defined __CYGWIN__
  43
  44 # define WIN32_LEAN_AND_MEAN
  45 # include <windows.h>
  46
  47 /* The return value of _spawnvp() is really a process handle as returned
  48    by CreateProcess().  Therefore we can kill it using TerminateProcess.  */
  49 # define kill(pid,sig) TerminateProcess ((HANDLE) (pid), sig)
  50
  51 #endif
  52
  53
  54 /* Type of an entry in the slaves array.
  55    The 'used' bit determines whether this entry is currently in use.
  56    (If pid_t was an atomic type like sig_atomic_t, we could just set the
  57    'child' field to 0 when unregistering a slave process, and wouldn't need
  58    the 'used' field.)
  59    The 'used' and 'child' fields are accessed from within the cleanup_slaves()
  60    action, therefore we mark them as 'volatile'.  */
  61 typedef struct
  62 {
  63   volatile sig_atomic_t used;
  64   volatile pid_t child;
  65 }
  66 slaves_entry_t;
  67
  68 /* The registered slave subprocesses.  */
  69 static slaves_entry_t static_slaves[32];
  70 static slaves_entry_t * volatile slaves = static_slaves;
  71 static sig_atomic_t volatile slaves_count = 0;
  72 static size_t slaves_allocated = SIZEOF (static_slaves);
  73
  74 /* The termination signal for slave subprocesses.
  75    2003-10-07:  Terminator becomes Governator.  */
  76 #ifdef SIGHUP
  77 # define TERMINATOR SIGHUP
  78 #else
  79 # define TERMINATOR SIGTERM
  80 #endif
  81
  82 /* The cleanup action.  It gets called asynchronously.  */
  83 static _GL_ASYNC_SAFE void
  84 cleanup_slaves (void)
  85 {
  86   for (;;)
  87     {
  88       /* Get the last registered slave.  */
  89       size_t n = slaves_count;
  90       if (n == 0)
  91         break;
  92       n--;
  93       slaves_count = n;
  94       /* Skip unused entries in the slaves array.  */
  95       if (slaves[n].used)
  96         {
  97           pid_t slave = slaves[n].child;
  98
  99           /* Kill the slave.  */
 100           kill (slave, TERMINATOR);
 101         }
 102     }
 103 }
 104
 105 /* The cleanup action, taking a signal argument.
 106    It gets called asynchronously.  */
 107 static _GL_ASYNC_SAFE void
 108 cleanup_slaves_action (int sig _GL_UNUSED)
 109 {
 110   cleanup_slaves ();
 111 }
 112
 113 /* Register a subprocess as being a slave process.  This means that the
 114    subprocess will be terminated when its creator receives a catchable fatal
 115    signal or exits normally.  Registration ends when wait_subprocess()
 116    notices that the subprocess has exited.  */
 117 void
 118 register_slave_subprocess (pid_t child)
 119 {
 120   static bool cleanup_slaves_registered = false;
 121   if (!cleanup_slaves_registered)
 122     {
 123       atexit (cleanup_slaves);
 124       at_fatal_signal (cleanup_slaves_action);
 125       cleanup_slaves_registered = true;
 126     }
 127
 128   /* Try to store the new slave in an unused entry of the slaves array.  */
 129   {
 130     slaves_entry_t *s = slaves;
 131     slaves_entry_t *s_end = s + slaves_count;
 132
 133     for (; s < s_end; s++)
 134       if (!s->used)
 135         {
 136           /* The two uses of 'volatile' in the slaves_entry_t type above
 137              (and ISO C 99 section 5.1.2.3.(5)) ensure that we mark the
 138              entry as used only after the child pid has been written to the
 139              memory location s->child.  */
 140           s->child = child;
 141           s->used = 1;
 142           return;
 143         }
 144   }
 145
 146   if (slaves_count == slaves_allocated)
 147     {
 148       /* Extend the slaves array.  Note that we cannot use xrealloc(),
 149          because then the cleanup_slaves() function could access an already
 150          deallocated array.  */
 151       slaves_entry_t *old_slaves = slaves;
 152       size_t new_slaves_allocated = 2 * slaves_allocated;
 153       slaves_entry_t *new_slaves =
 154         (slaves_entry_t *)
 155         malloc (new_slaves_allocated * sizeof (slaves_entry_t));
 156       if (new_slaves == NULL)
 157         {
 158           /* xalloc_die() will call exit() which will invoke cleanup_slaves().
 159              Additionally we need to kill child, because it's not yet among
 160              the slaves list.  */
 161           kill (child, TERMINATOR);
 162           xalloc_die ();
 163         }
 164       memcpy (new_slaves, old_slaves,
 165               slaves_allocated * sizeof (slaves_entry_t));
 166       slaves = new_slaves;
 167       slaves_allocated = new_slaves_allocated;
 168       /* Now we can free the old slaves array.  */
 169       if (old_slaves != static_slaves)
 170         free (old_slaves);
 171     }
 172   /* The three uses of 'volatile' in the types above (and ISO C 99 section
 173      5.1.2.3.(5)) ensure that we increment the slaves_count only after the
 174      new slave and its 'used' bit have been written to the memory locations
 175      that make up slaves[slaves_count].  */
 176   slaves[slaves_count].child = child;
 177   slaves[slaves_count].used = 1;
 178   slaves_count++;
 179 }
 180
 181 /* Unregister a child from the list of slave subprocesses.  */
 182 static void
 183 unregister_slave_subprocess (pid_t child)
 184 {
 185   /* The easiest way to remove an entry from a list that can be used by
 186      an asynchronous signal handler is just to mark it as unused.  For this,
 187      we rely on sig_atomic_t.  */
 188   slaves_entry_t *s = slaves;
 189   slaves_entry_t *s_end = s + slaves_count;
 190
 191   for (; s < s_end; s++)
 192     if (s->used && s->child == child)
 193       s->used = 0;
 194 }
 195
 196
 197 /* Wait for a subprocess to finish.  Return its exit code.
 198    If it didn't terminate correctly, exit if exit_on_error is true, otherwise
 199    return 127.  */
 200 int
 201 wait_subprocess (pid_t child, const char *progname,
 202                  bool ignore_sigpipe, bool null_stderr,
 203                  bool slave_process, bool exit_on_error,
 204                  int *termsigp)
 205 {
 206 #if HAVE_WAITID && defined WNOWAIT && 0
 207   /* Commented out because waitid() without WEXITED and with WNOWAIT doesn't
 208      work: On Solaris 7 and OSF/1 4.0, it returns -1 and sets errno = ECHILD,
 209      and on HP-UX 10.20 it just hangs.  */
 210   /* Use of waitid() with WNOWAIT avoids a race condition: If slave_process is
 211      true, and this process sleeps a very long time between the return from
 212      waitpid() and the execution of unregister_slave_subprocess(), and
 213      meanwhile another process acquires the same PID as child, and then - still
 214      before unregister_slave_subprocess() - this process gets a fatal signal,
 215      it would kill the other totally unrelated process.  */
 216   siginfo_t info;
 217
 218   if (termsigp != NULL)
 219     *termsigp = 0;
 220   for (;;)
 221     {
 222       if (waitid (P_PID, child, &info, WEXITED | (slave_process ? WNOWAIT : 0))
 223           < 0)
 224         {
 225 # ifdef EINTR
 226           if (errno == EINTR)
 227             continue;
 228 # endif
 229           if (exit_on_error || !null_stderr)
 230             error (exit_on_error ? EXIT_FAILURE : 0, errno,
 231                    _("%s subprocess"), progname);
 232           return 127;
 233         }
 234
 235       /* info.si_code is set to one of CLD_EXITED, CLD_KILLED, CLD_DUMPED,
 236          CLD_TRAPPED, CLD_STOPPED, CLD_CONTINUED.  Loop until the program
 237          terminates.  */
 238       if (info.si_code == CLD_EXITED
 239           || info.si_code == CLD_KILLED || info.si_code == CLD_DUMPED)
 240         break;
 241     }
 242
 243   /* The child process has exited or was signalled.  */
 244
 245   if (slave_process)
 246     {
 247       /* Unregister the child from the list of slave subprocesses, so that
 248          later, when we exit, we don't kill a totally unrelated process which
 249          may have acquired the same pid.  */
 250       unregister_slave_subprocess (child);
 251
 252       /* Now remove the zombie from the process list.  */
 253       for (;;)
 254         {
 255           if (waitid (P_PID, child, &info, WEXITED) < 0)
 256             {
 257 # ifdef EINTR
 258               if (errno == EINTR)
 259                 continue;
 260 # endif
 261               if (exit_on_error || !null_stderr)
 262                 error (exit_on_error ? EXIT_FAILURE : 0, errno,
 263                        _("%s subprocess"), progname);
 264               return 127;
 265             }
 266           break;
 267         }
 268     }
 269
 270   switch (info.si_code)
 271     {
 272     case CLD_KILLED:
 273     case CLD_DUMPED:
 274       if (termsigp != NULL)
 275         *termsigp = info.si_status; /* TODO: or info.si_signo? */
 276 # ifdef SIGPIPE
 277       if (info.si_status == SIGPIPE && ignore_sigpipe)
 278         return 0;
 279 # endif
 280       if (exit_on_error || (!null_stderr && termsigp == NULL))
 281         error (exit_on_error ? EXIT_FAILURE : 0, 0,
 282                _("%s subprocess got fatal signal %d"),
 283                progname, info.si_status);
 284       return 127;
 285     case CLD_EXITED:
 286       if (info.si_status == 127)
 287         {
 288           if (exit_on_error || !null_stderr)
 289             error (exit_on_error ? EXIT_FAILURE : 0, 0,
 290                    _("%s subprocess failed"), progname);
 291           return 127;
 292         }
 293       return info.si_status;
 294     default:
 295       abort ();
 296     }
 297 #else
 298   /* waitpid() is just as portable as wait() nowadays.  */
 299   int status;
 300
 301   if (termsigp != NULL)
 302     *termsigp = 0;
 303   status = 0;
 304   for (;;)
 305     {
 306       int result = waitpid (child, &status, 0);
 307
 308       if (result != child)
 309         {
 310 # ifdef EINTR
 311           if (errno == EINTR)
 312             continue;
 313 # endif
 314 # if 0 /* defined ECHILD */
 315           if (errno == ECHILD)
 316             {
 317               /* Child process nonexistent?! Assume it terminated
 318                  successfully.  */
 319               status = 0;
 320               break;
 321             }
 322 # endif
 323           if (exit_on_error || !null_stderr)
 324             error (exit_on_error ? EXIT_FAILURE : 0, errno,
 325                    _("%s subprocess"), progname);
 326           return 127;
 327         }
 328
 329       /* One of WIFSIGNALED (status), WIFEXITED (status), WIFSTOPPED (status)
 330          must always be true, since we did not specify WCONTINUED in the
 331          waitpid() call.  Loop until the program terminates.  */
 332       if (!WIFSTOPPED (status))
 333         break;
 334     }
 335
 336   /* The child process has exited or was signalled.  */
 337
 338   if (slave_process)
 339     /* Unregister the child from the list of slave subprocesses, so that
 340        later, when we exit, we don't kill a totally unrelated process which
 341        may have acquired the same pid.  */
 342     unregister_slave_subprocess (child);
 343
 344   if (WIFSIGNALED (status))
 345     {
 346       if (termsigp != NULL)
 347         *termsigp = WTERMSIG (status);
 348 # ifdef SIGPIPE
 349       if (WTERMSIG (status) == SIGPIPE && ignore_sigpipe)
 350         return 0;
 351 # endif
 352       if (exit_on_error || (!null_stderr && termsigp == NULL))
 353         error (exit_on_error ? EXIT_FAILURE : 0, 0,
 354                _("%s subprocess got fatal signal %d"),
 355                progname, (int) WTERMSIG (status));
 356       return 127;
 357     }
 358   if (!WIFEXITED (status))
 359     abort ();
 360   if (WEXITSTATUS (status) == 127)
 361     {
 362       if (exit_on_error || !null_stderr)
 363         error (exit_on_error ? EXIT_FAILURE : 0, 0,
 364                _("%s subprocess failed"), progname);
 365       return 127;
 366     }
 367   return WEXITSTATUS (status);
 368 #endif
 369 }