nptl/sem_wait.c

   1 /* sem_wait -- wait on a semaphore.  Generic futex-using version.
   2    Copyright (C) 2003-2016 Free Software Foundation, Inc.
   3    This file is part of the GNU C Library.
   4    Contributed by Paul Mackerras <paulus@au.ibm.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 <lowlevellock.h>       /* lll_futex* used by the old code.  */
  21 #include "sem_waitcommon.c"
  22
  23 int
  24 __new_sem_wait (sem_t *sem)
  25 {
  26   if (__new_sem_wait_fast ((struct new_sem *) sem, 0) == 0)
  27     return 0;
  28   else
  29     return __new_sem_wait_slow((struct new_sem *) sem, NULL);
  30 }
  31 versioned_symbol (libpthread, __new_sem_wait, sem_wait, GLIBC_2_1);
  32
  33 #if SHLIB_COMPAT (libpthread, GLIBC_2_0, GLIBC_2_1)
  34 int
  35 attribute_compat_text_section
  36 __old_sem_wait (sem_t *sem)
  37 {
  38   int *futex = (int *) sem;
  39   int err;
  40
  41   do
  42     {
  43       if (atomic_decrement_if_positive (futex) > 0)
  44         return 0;
  45
  46       /* Enable asynchronous cancellation.  Required by the standard.  */
  47       int oldtype = __pthread_enable_asynccancel ();
  48
  49       /* Always assume the semaphore is shared.  */
  50       err = lll_futex_wait (futex, 0, LLL_SHARED);
  51
  52       /* Disable asynchronous cancellation.  */
  53       __pthread_disable_asynccancel (oldtype);
  54     }
  55   while (err == 0 || err == -EWOULDBLOCK);
  56
  57   __set_errno (-err);
  58   return -1;
  59 }
  60
  61 compat_symbol (libpthread, __old_sem_wait, sem_wait, GLIBC_2_0);
  62 #endif
  63
  64 int
  65 __new_sem_trywait (sem_t *sem)
  66 {
  67   /* We must not fail spuriously, so require a definitive result even if this
  68      may lead to a long execution time.  */
  69   if (__new_sem_wait_fast ((struct new_sem *) sem, 1) == 0)
  70     return 0;
  71   __set_errno (EAGAIN);
  72   return -1;
  73 }
  74 versioned_symbol (libpthread, __new_sem_trywait, sem_trywait, GLIBC_2_1);
  75 #if SHLIB_COMPAT (libpthread, GLIBC_2_0, GLIBC_2_1)
  76 int
  77 __old_sem_trywait (sem_t *sem)
  78 {
  79   int *futex = (int *) sem;
  80   int val;
  81
  82   if (*futex > 0)
  83     {
  84       val = atomic_decrement_if_positive (futex);
  85       if (val > 0)
  86         return 0;
  87     }
  88
  89   __set_errno (EAGAIN);
  90   return -1;
  91 }
  92 compat_symbol (libpthread, __old_sem_trywait, sem_trywait, GLIBC_2_0);
  93 #endif