lib/pthread_sigmask.c

/* POSIX compatible signal blocking for threads.
   Copyright (C) 2011-2026 Free Software Foundation, Inc.

   This file 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 file 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 program.  If not, see <https://www.gnu.org/licenses/>.  */

#include <config.h>

/* Specification.  */
#include <signal.h>

#include <errno.h>
#include <stddef.h>

#if PTHREAD_SIGMASK_INEFFECTIVE
# include <string.h>
#endif

int
pthread_sigmask (int how, const sigset_t *new_mask, sigset_t *old_mask)
#undef pthread_sigmask
{
#if HAVE_PTHREAD_SIGMASK
# if PTHREAD_SIGMASK_INEFFECTIVE
  sigset_t omask;
  sigset_t *old_mask_ptr = &omask;
  sigemptyset (&omask);
  /* Add a signal unlikely to be blocked, so that OMASK_COPY
     is unlikely to match the actual mask.  */
  sigaddset (&omask, SIGILL);
  sigset_t omask_copy;
  memcpy (&omask_copy, &omask, sizeof omask);
# else
  sigset_t *old_mask_ptr = old_mask;
# endif

  int ret = pthread_sigmask (how, new_mask, old_mask_ptr);

# if PTHREAD_SIGMASK_INEFFECTIVE
  if (ret == 0)
    {
      /* Detect whether pthread_sigmask is currently ineffective.
         Don't cache the information: libpthread.so could be dynamically
         loaded after the program started and after pthread_sigmask was
         called for the first time.  */
      if (memeq (&omask_copy, &omask, sizeof omask)
          && pthread_sigmask (1729, &omask_copy, NULL) == 0)
        {
          /* pthread_sigmask is currently ineffective.  The program is not
             linked to -lpthread.  So use sigprocmask instead.  */
          return (sigprocmask (how, new_mask, old_mask) < 0 ? errno : 0);
        }

      if (old_mask)
        memcpy (old_mask, &omask, sizeof omask);
    }
# endif
# if PTHREAD_SIGMASK_FAILS_WITH_ERRNO
  if (ret == -1)
    return errno;
# endif
  return ret;
#else
  int ret = sigprocmask (how, new_mask, old_mask);
  return (ret < 0 ? errno : 0);
#endif
}