nptl/sem_wait.c

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