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glibc  2.9
sem_post.c
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00001 /* sem_post -- post to a POSIX semaphore.  Generic futex-using version.
00002    Copyright (C) 2003, 2004, 2007, 2008 Free Software Foundation, Inc.
00003    This file is part of the GNU C Library.
00004    Contributed by Jakub Jelinek <jakub@redhat.com>, 2003.
00005 
00006    The GNU C Library is free software; you can redistribute it and/or
00007    modify it under the terms of the GNU Lesser General Public
00008    License as published by the Free Software Foundation; either
00009    version 2.1 of the License, or (at your option) any later version.
00010 
00011    The GNU C Library is distributed in the hope that it will be useful,
00012    but WITHOUT ANY WARRANTY; without even the implied warranty of
00013    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
00014    Lesser General Public License for more details.
00015 
00016    You should have received a copy of the GNU Lesser General Public
00017    License along with the GNU C Library; if not, write to the Free
00018    Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
00019    02111-1307 USA.  */
00020 
00021 #include <errno.h>
00022 #include <sysdep.h>
00023 #include <lowlevellock.h>
00024 #include <internaltypes.h>
00025 #include <semaphore.h>
00026 
00027 #include <shlib-compat.h>
00028 
00029 int
00030 __new_sem_post (sem_t *sem)
00031 {
00032   struct new_sem *isem = (struct new_sem *) sem;
00033 
00034   __typeof (isem->value) cur;
00035   do
00036     {
00037       cur = isem->value;
00038       if (isem->value == SEM_VALUE_MAX)
00039        {
00040          __set_errno (EOVERFLOW);
00041          return -1;
00042        }
00043     }
00044   while (atomic_compare_and_exchange_bool_acq (&isem->value, cur + 1, cur));
00045 
00046   atomic_full_barrier ();
00047   if (isem->nwaiters > 0)
00048     {
00049       int err = lll_futex_wake (&isem->value, 1,
00050                             isem->private ^ FUTEX_PRIVATE_FLAG);
00051       if (__builtin_expect (err, 0) < 0)
00052        {
00053          __set_errno (-err);
00054          return -1;
00055        }
00056     }
00057   return 0;
00058 }
00059 versioned_symbol (libpthread, __new_sem_post, sem_post, GLIBC_2_1);
00060 
00061 
00062 #if SHLIB_COMPAT (libpthread, GLIBC_2_0, GLIBC_2_1)
00063 int
00064 attribute_compat_text_section
00065 __old_sem_post (sem_t *sem)
00066 {
00067   int *futex = (int *) sem;
00068 
00069   int nr = atomic_increment_val (futex);
00070   /* We always have to assume it is a shared semaphore.  */
00071   int err = lll_futex_wake (futex, 1, LLL_SHARED);
00072   if (__builtin_expect (err, 0) < 0)
00073     {
00074       __set_errno (-err);
00075       return -1;
00076     }
00077   return 0;
00078 }
00079 compat_symbol (libpthread, __old_sem_post, sem_post, GLIBC_2_0);
00080 #endif