sysdeps/htl/sem-post.c

   1 /* Post a semaphore.  Generic version.
   2    Copyright (C) 2005-2019 Free Software Foundation, Inc.
   3    This file is part of the GNU C Library.
   4
   5    The GNU C Library is free software; you can redistribute it and/or
   6    modify it under the terms of the GNU Lesser General Public
   7    License as published by the Free Software Foundation; either
   8    version 2.1 of the License, or (at your option) any later version.
   9
  10    The GNU C Library 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 GNU
  13    Lesser General Public License for more details.
  14
  15    You should have received a copy of the GNU Lesser General Public
  16    License along with the GNU C Library;  if not, see
  17    <http://www.gnu.org/licenses/>.  */
  18
  19 #include <semaphore.h>
  20 #include <assert.h>
  21
  22 #include <pt-internal.h>
  23
  24 int
  25 __sem_post (sem_t *sem)
  26 {
  27   struct __pthread *wakeup;
  28
  29   __pthread_spin_lock (&sem->__lock);
  30   if (sem->__value > 0)
  31     /* Do a quick up.  */
  32     {
  33       assert (sem->__queue == NULL);
  34       sem->__value++;
  35       __pthread_spin_unlock (&sem->__lock);
  36       return 0;
  37     }
  38
  39   if (sem->__queue == NULL)
  40     /* No one waiting.  */
  41     {
  42       sem->__value = 1;
  43       __pthread_spin_unlock (&sem->__lock);
  44       return 0;
  45     }
  46
  47   /* Wake someone up.  */
  48
  49   /* First dequeue someone.  */
  50   wakeup = sem->__queue;
  51   __pthread_dequeue (wakeup);
  52
  53   /* Then drop the lock and transfer control.  */
  54   __pthread_spin_unlock (&sem->__lock);
  55
  56   __pthread_wakeup (wakeup);
  57
  58   return 0;
  59 }
  60
  61 strong_alias (__sem_post, sem_post);