native_client_sdk/src/libraries/third_party/pthreads-win32/sem_trywait.c

   1 /*
   2  * -------------------------------------------------------------
   3  *
   4  * Module: sem_trywait.c
   5  *
   6  * Purpose:
   7  *      Semaphores aren't actually part of the PThreads standard.
   8  *      They are defined by the POSIX Standard:
   9  *
  10  *              POSIX 1003.1b-1993      (POSIX.1b)
  11  *
  12  * -------------------------------------------------------------
  13  *
  14  * --------------------------------------------------------------------------
  15  *
  16  *      Pthreads-win32 - POSIX Threads Library for Win32
  17  *      Copyright(C) 1998 John E. Bossom
  18  *      Copyright(C) 1999,2005 Pthreads-win32 contributors
  19  *
  20  *      Contact Email: rpj@callisto.canberra.edu.au
  21  *
  22  *      The current list of contributors is contained
  23  *      in the file CONTRIBUTORS included with the source
  24  *      code distribution. The list can also be seen at the
  25  *      following World Wide Web location:
  26  *      http://sources.redhat.com/pthreads-win32/contributors.html
  27  *
  28  *      This library is free software; you can redistribute it and/or
  29  *      modify it under the terms of the GNU Lesser General Public
  30  *      License as published by the Free Software Foundation; either
  31  *      version 2 of the License, or (at your option) any later version.
  32  *
  33  *      This library is distributed in the hope that it will be useful,
  34  *      but WITHOUT ANY WARRANTY; without even the implied warranty of
  35  *      MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  36  *      Lesser General Public License for more details.
  37  *
  38  *      You should have received a copy of the GNU Lesser General Public
  39  *      License along with this library in the file COPYING.LIB;
  40  *      if not, write to the Free Software Foundation, Inc.,
  41  *      59 Temple Place - Suite 330, Boston, MA 02111-1307, USA
  42  */
  43
  44 #include "pthread.h"
  45 #include "semaphore.h"
  46 #include "implement.h"
  47
  48
  49 int
  50 sem_trywait (sem_t * sem)
  51      /*
  52       * ------------------------------------------------------
  53       * DOCPUBLIC
  54       *      This function tries to wait on a semaphore.
  55       *
  56       * PARAMETERS
  57       *      sem
  58       *              pointer to an instance of sem_t
  59       *
  60       * DESCRIPTION
  61       *      This function tries to wait on a semaphore. If the
  62       *      semaphore value is greater than zero, it decreases
  63       *      its value by one. If the semaphore value is zero, then
  64       *      this function returns immediately with the error EAGAIN
  65       *
  66       * RESULTS
  67       *              0               successfully decreased semaphore,
  68       *              -1              failed, error in errno
  69       * ERRNO
  70       *              EAGAIN          the semaphore was already locked,
  71       *              EINVAL          'sem' is not a valid semaphore,
  72       *              ENOTSUP         sem_trywait is not supported,
  73       *              EINTR           the function was interrupted by a signal,
  74       *              EDEADLK         a deadlock condition was detected.
  75       *
  76       * ------------------------------------------------------
  77       */
  78 {
  79   int result = 0;
  80   sem_t s = *sem;
  81
  82   if (s == NULL)
  83     {
  84       result = EINVAL;
  85     }
  86   else if ((result = pthread_mutex_lock (&s->lock)) == 0)
  87     {
  88       /* See sem_destroy.c
  89        */
  90      if (*sem == NULL)
  91         {
  92           (void) pthread_mutex_unlock (&s->lock);
  93           errno = EINVAL;
  94           return -1;
  95         }
  96
  97       if (s->value > 0)
  98         {
  99           s->value--;
 100         }
 101       else
 102         {
 103           result = EAGAIN;
 104         }
 105
 106       (void) pthread_mutex_unlock (&s->lock);
 107     }
 108
 109   if (result != 0)
 110     {
 111       errno = result;
 112       return -1;
 113     }
 114
 115   return 0;
 116
 117 }                               /* sem_trywait */