glibc/sysdeps/htl/sem-post.c

/* Post a semaphore.  Generic version.
   Copyright (C) 2005-2018 Free Software Foundation, Inc.
   This file is part of the GNU C Library.

   The GNU C Library is free software; you can redistribute it and/or
   modify it under the terms of the GNU Library General Public License as
   published by the Free Software Foundation; either version 2 of the
   License, or (at your option) any later version.

   The GNU C 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
   Library General Public License for more details.

   You should have received a copy of the GNU Library General Public
   License along with the GNU C Library; see the file COPYING.LIB.  If
   not, see <http://www.gnu.org/licenses/>.  */

#include <semaphore.h>
#include <assert.h>

#include <pt-internal.h>

int
__sem_post (sem_t *sem)
{
  struct __pthread *wakeup;

  __pthread_spin_lock (&sem->__lock);
  if (sem->__value > 0)
    /* Do a quick up.  */
    {
      assert (sem->__queue == NULL);
      sem->__value++;
      __pthread_spin_unlock (&sem->__lock);
      return 0;
    }

  if (sem->__queue == NULL)
    /* No one waiting.  */
    {
      sem->__value = 1;
      __pthread_spin_unlock (&sem->__lock);
      return 0;
    }

  /* Wake someone up.  */

  /* First dequeue someone.  */
  wakeup = sem->__queue;
  __pthread_dequeue (wakeup);

  /* Then drop the lock and transfer control.  */
  __pthread_spin_unlock (&sem->__lock);

  __pthread_wakeup (wakeup);

  return 0;
}

strong_alias (__sem_post, sem_post);