nptl/sem_post.c

   1 /* sem_post -- post to a POSIX semaphore.  Generic futex-using version.
   2    Copyright (C) 2003-2015 Free Software Foundation, Inc.
   3    This file is part of the GNU C Library.
   4    Contributed by Jakub Jelinek <jakub@redhat.com>, 2003.
   5
   6    The GNU C Library is free software; you can redistribute it and/or
   7    modify it under the terms of the GNU Lesser General Public
   8    License as published by the Free Software Foundation; either
   9    version 2.1 of the License, or (at your option) any later version.
  10
  11    The GNU C Library is distributed in the hope that it will be useful,
  12    but WITHOUT ANY WARRANTY; without even the implied warranty of
  13    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  14    Lesser General Public License for more details.
  15
  16    You should have received a copy of the GNU Lesser General Public
  17    License along with the GNU C Library; if not, see
  18    <http://www.gnu.org/licenses/>.  */
  19
  20 #include <atomic.h>
  21 #include <errno.h>
  22 #include <sysdep.h>
  23 #include <lowlevellock.h>
  24 #include <internaltypes.h>
  25 #include <semaphore.h>
  26
  27 #include <shlib-compat.h>
  28
  29 int
  30 __new_sem_post (sem_t *sem)
  31 {
  32   struct new_sem *isem = (struct new_sem *) sem;
  33
  34   __typeof (isem->value) cur;
  35   do
  36     {
  37       cur = isem->value;
  38       if (isem->value == SEM_VALUE_MAX)
  39         {
  40           __set_errno (EOVERFLOW);
  41           return -1;
  42         }
  43     }
  44   while (atomic_compare_and_exchange_bool_rel (&isem->value, cur + 1, cur));
  45
  46   atomic_full_barrier ();
  47   if (isem->nwaiters > 0)
  48     {
  49       int err = lll_futex_wake (&isem->value, 1,
  50                                 isem->private ^ FUTEX_PRIVATE_FLAG);
  51       if (__builtin_expect (err, 0) < 0)
  52         {
  53           __set_errno (-err);
  54           return -1;
  55         }
  56     }
  57   return 0;
  58 }
  59 versioned_symbol (libpthread, __new_sem_post, sem_post, GLIBC_2_1);
  60
  61
  62 #if SHLIB_COMPAT (libpthread, GLIBC_2_0, GLIBC_2_1)
  63 int
  64 attribute_compat_text_section
  65 __old_sem_post (sem_t *sem)
  66 {
  67   int *futex = (int *) sem;
  68
  69   (void) atomic_increment_val (futex);
  70   /* We always have to assume it is a shared semaphore.  */
  71   int err = lll_futex_wake (futex, 1, LLL_SHARED);
  72   if (__builtin_expect (err, 0) < 0)
  73     {
  74       __set_errno (-err);
  75       return -1;
  76     }
  77   return 0;
  78 }
  79 compat_symbol (libpthread, __old_sem_post, sem_post, GLIBC_2_0);
  80 #endif