1  /* Post a semaphore.  Generic version.
       2     Copyright (C) 2005-2023 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);