nptl/sysdeps/unix/sysv/linux/sem_wait.c

   1 /* sem_wait -- wait on a semaphore.  Generic futex-using version.
   2    Copyright (C) 2003, 2007 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, write to the Free
  18    Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
  19    02111-1307 USA.  */
  20
  21 #include <errno.h>
  22 #include <sysdep.h>
  23 #include <lowlevellock.h>
  24 #include <internaltypes.h>
  25 #include <semaphore.h>
  26
  27 #include <pthreadP.h>
  28 #include <shlib-compat.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
  41 int
  42 __new_sem_wait (sem_t *sem)
  43 {
  44   struct new_sem *isem = (struct new_sem *) sem;
  45   int err;
  46
  47   if (atomic_decrement_if_positive (&isem->value) > 0)
  48     return 0;
  49
  50   atomic_increment (&isem->nwaiters);
  51
  52   pthread_cleanup_push (__sem_wait_cleanup, isem);
  53
  54   while (1)
  55     {
  56       /* Enable asynchronous cancellation.  Required by the standard.  */
  57       int oldtype = __pthread_enable_asynccancel ();
  58
  59       err = lll_futex_wait (&isem->value, 0,
  60                             // XYZ check mutex flag
  61                             LLL_SHARED);
  62
  63       /* Disable asynchronous cancellation.  */
  64       __pthread_disable_asynccancel (oldtype);
  65
  66       if (err != 0 && err != -EWOULDBLOCK)
  67         {
  68           __set_errno (-err);
  69           err = -1;
  70           break;
  71         }
  72
  73       if (atomic_decrement_if_positive (&isem->value) > 0)
  74         {
  75           err = 0;
  76           break;
  77         }
  78     }
  79
  80   pthread_cleanup_pop (0);
  81
  82   atomic_decrement (&isem->nwaiters);
  83
  84   return err;
  85 }
  86 versioned_symbol (libpthread, __new_sem_wait, sem_wait, GLIBC_2_1);
  87
  88
  89 #if SHLIB_COMPAT (libpthread, GLIBC_2_0, GLIBC_2_1)
  90 int
  91 attribute_compat_text_section
  92 __old_sem_wait (sem_t *sem)
  93 {
  94   int *futex = (int *) sem;
  95   int err;
  96
  97   do
  98     {
  99       if (atomic_decrement_if_positive (futex) > 0)
 100         return 0;
 101
 102       /* Enable asynchronous cancellation.  Required by the standard.  */
 103       int oldtype = __pthread_enable_asynccancel ();
 104
 105       /* Always assume the semaphore is shared.  */
 106       err = lll_futex_wait (futex, 0, LLL_SHARED);
 107
 108       /* Disable asynchronous cancellation.  */
 109       __pthread_disable_asynccancel (oldtype);
 110     }
 111   while (err == 0 || err == -EWOULDBLOCK);
 112
 113   __set_errno (-err);
 114   return -1;
 115 }
 116
 117 compat_symbol (libpthread, __old_sem_wait, sem_wait, GLIBC_2_0);
 118 #endif