sysdeps/htl/sem-waitfast.c

   1 /* Lock a semaphore if it does not require blocking.  Generic version.
   2    Copyright (C) 2005-2020 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 <errno.h>
  21
  22 #include <pt-internal.h>
  23
  24 int
  25 __sem_waitfast (struct new_sem *isem, int definitive_result)
  26 {
  27 #if __HAVE_64B_ATOMICS
  28   uint64_t d = atomic_load_relaxed (&isem->data);
  29
  30   do
  31     {
  32       if ((d & SEM_VALUE_MASK) == 0)
  33         break;
  34       if (atomic_compare_exchange_weak_acquire (&isem->data, &d, d - 1))
  35         /* Successful down.  */
  36         return 0;
  37     }
  38   while (definitive_result);
  39   return -1;
  40 #else
  41   unsigned v = atomic_load_relaxed (&isem->value);
  42
  43   do
  44     {
  45       if ((v >> SEM_VALUE_SHIFT) == 0)
  46         break;
  47       if (atomic_compare_exchange_weak_acquire (&isem->value,
  48             &v, v - (1 << SEM_VALUE_SHIFT)))
  49         /* Successful down.  */
  50         return 0;
  51     }
  52   while (definitive_result);
  53   return -1;
  54 #endif
  55 }