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 <errno.h>
  21 #include <sysdep.h>
  22 #include <lowlevellock.h>
  23 #include <internaltypes.h>
  24 #include <semaphore.h>
  25
  26 #include <pthreadP.h>
  27 #include <shlib-compat.h>
  28 #include <atomic.h>
  29
  30
  31 void
  32 attribute_hidden
  33 __sem_wait_cleanup (void *arg)
  34 {
  35   struct new_sem *isem = (struct new_sem *) arg;
  36
  37   atomic_decrement (&isem->nwaiters);
  38 }
  39
  40 /* This is in a seperate function in order to make sure gcc
  41    puts the call site into an exception region, and thus the
  42    cleanups get properly run.  */
  43 static int
  44 __attribute__ ((noinline))
  45 do_futex_wait (struct new_sem *isem)
  46 {
  47   int err, oldtype = __pthread_enable_asynccancel ();
  48
  49   err = lll_futex_wait (&isem->value, 0, isem->private ^ FUTEX_PRIVATE_FLAG);
  50
  51   __pthread_disable_asynccancel (oldtype);
  52   return err;
  53 }
  54
  55 int
  56 __new_sem_wait (sem_t *sem)
  57 {
  58   struct new_sem *isem = (struct new_sem *) sem;
  59   int err;
  60
  61   if (atomic_decrement_if_positive (&isem->value) > 0)
  62     return 0;
  63
  64   atomic_increment (&isem->nwaiters);
  65
  66   pthread_cleanup_push (__sem_wait_cleanup, isem);
  67
  68   while (1)
  69     {
  70       err = do_futex_wait(isem);
  71       if (err != 0 && err != -EWOULDBLOCK)
  72         {
  73           __set_errno (-err);
  74           err = -1;
  75           break;
  76         }
  77
  78       if (atomic_decrement_if_positive (&isem->value) > 0)
  79         {
  80           err = 0;
  81           break;
  82         }
  83     }
  84
  85   pthread_cleanup_pop (0);
  86
  87   atomic_decrement (&isem->nwaiters);
  88
  89   return err;
  90 }
  91 versioned_symbol (libpthread, __new_sem_wait, sem_wait, GLIBC_2_1);
  92
  93
  94 #if SHLIB_COMPAT (libpthread, GLIBC_2_0, GLIBC_2_1)
  95 int
  96 attribute_compat_text_section
  97 __old_sem_wait (sem_t *sem)
  98 {
  99   int *futex = (int *) sem;
 100   int err;
 101
 102   do
 103     {
 104       if (atomic_decrement_if_positive (futex) > 0)
 105         return 0;
 106
 107       /* Enable asynchronous cancellation.  Required by the standard.  */
 108       int oldtype = __pthread_enable_asynccancel ();
 109
 110       /* Always assume the semaphore is shared.  */
 111       err = lll_futex_wait (futex, 0, LLL_SHARED);
 112
 113       /* Disable asynchronous cancellation.  */
 114       __pthread_disable_asynccancel (oldtype);
 115     }
 116   while (err == 0 || err == -EWOULDBLOCK);
 117
 118   __set_errno (-err);
 119   return -1;
 120 }
 121
 122 compat_symbol (libpthread, __old_sem_wait, sem_wait, GLIBC_2_0);
 123 #endif