sysdeps/htl/sem-post.c

   1 /* Post a semaphore.  Generic version.
   2    Copyright (C) 2005-2024 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    <https://www.gnu.org/licenses/>.  */
  18
  19 #include <semaphore.h>
  20 #include <assert.h>
  21
  22 #include <hurdlock.h>
  23 #include <hurd.h>
  24
  25 #include <pt-internal.h>
  26
  27 int
  28 __sem_post (sem_t *sem)
  29 {
  30   struct new_sem *isem = (struct new_sem *) sem;
  31   int flags = isem->pshared ? GSYNC_SHARED : 0;
  32
  33 #if __HAVE_64B_ATOMICS
  34   uint64_t d = atomic_load_relaxed (&isem->data);
  35
  36   do
  37     {
  38       if ((d & SEM_VALUE_MASK) == SEM_VALUE_MAX)
  39         return __hurd_fail (EOVERFLOW);
  40     }
  41   while (!atomic_compare_exchange_weak_release (&isem->data, &d, d + 1));
  42
  43   if ((d >> SEM_NWAITERS_SHIFT) != 0)
  44     /* Wake one waiter.  */
  45     __lll_wake (((unsigned int *) &isem->data) + SEM_VALUE_OFFSET, flags);
  46 #else
  47   unsigned int v = atomic_load_relaxed (&isem->value);
  48
  49   do
  50     {
  51       if ((v >> SEM_VALUE_SHIFT) == SEM_VALUE_MAX)
  52         return __hurd_fail (EOVERFLOW);
  53     }
  54   while (!atomic_compare_exchange_weak_release
  55           (&isem->value, &v, v + (1 << SEM_VALUE_SHIFT)));
  56
  57   if ((v & SEM_NWAITERS_MASK) != 0)
  58     /* Wake one waiter.  */
  59     __lll_wake (&isem->value, flags);
  60 #endif
  61
  62   return 0;
  63 }
  64 libpthread_hidden_def (__sem_post)
  65 strong_alias (__sem_post, sem_post);