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      1 /*
      2  * pthread_rwlock_trywrlock.c
      3  *
      4  * Description:
      5  * This translation unit implements read/write lock primitives.
      6  *
      7  * --------------------------------------------------------------------------
      8  *
      9  *      Pthreads-win32 - POSIX Threads Library for Win32
     10  *      Copyright(C) 1998 John E. Bossom
     11  *      Copyright(C) 1999,2005 Pthreads-win32 contributors
     12  *
     13  *      Contact Email: rpj (at) callisto.canberra.edu.au
     14  *
     15  *      The current list of contributors is contained
     16  *      in the file CONTRIBUTORS included with the source
     17  *      code distribution. The list can also be seen at the
     18  *      following World Wide Web location:
     19  *      http://sources.redhat.com/pthreads-win32/contributors.html
     20  *
     21  *      This library is free software; you can redistribute it and/or
     22  *      modify it under the terms of the GNU Lesser General Public
     23  *      License as published by the Free Software Foundation; either
     24  *      version 2 of the License, or (at your option) any later version.
     25  *
     26  *      This library is distributed in the hope that it will be useful,
     27  *      but WITHOUT ANY WARRANTY; without even the implied warranty of
     28  *      MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
     29  *      Lesser General Public License for more details.
     30  *
     31  *      You should have received a copy of the GNU Lesser General Public
     32  *      License along with this library in the file COPYING.LIB;
     33  *      if not, write to the Free Software Foundation, Inc.,
     34  *      59 Temple Place - Suite 330, Boston, MA 02111-1307, USA
     35  */
     36 
     37 #include <limits.h>
     38 
     39 #include "pthread.h"
     40 #include "implement.h"
     41 
     42 int
     43 pthread_rwlock_trywrlock (pthread_rwlock_t * rwlock)
     44 {
     45   int result, result1;
     46   pthread_rwlock_t rwl;
     47 
     48   if (rwlock == NULL || *rwlock == NULL)
     49     {
     50       return EINVAL;
     51     }
     52 
     53   /*
     54    * We do a quick check to see if we need to do more work
     55    * to initialise a static rwlock. We check
     56    * again inside the guarded section of ptw32_rwlock_check_need_init()
     57    * to avoid race conditions.
     58    */
     59   if (*rwlock == PTHREAD_RWLOCK_INITIALIZER)
     60     {
     61       result = ptw32_rwlock_check_need_init (rwlock);
     62 
     63       if (result != 0 && result != EBUSY)
     64 	{
     65 	  return result;
     66 	}
     67     }
     68 
     69   rwl = *rwlock;
     70 
     71   if (rwl->nMagic != PTW32_RWLOCK_MAGIC)
     72     {
     73       return EINVAL;
     74     }
     75 
     76   if ((result = pthread_mutex_trylock (&(rwl->mtxExclusiveAccess))) != 0)
     77     {
     78       return result;
     79     }
     80 
     81   if ((result =
     82        pthread_mutex_trylock (&(rwl->mtxSharedAccessCompleted))) != 0)
     83     {
     84       result1 = pthread_mutex_unlock (&(rwl->mtxExclusiveAccess));
     85       return ((result1 != 0) ? result1 : result);
     86     }
     87 
     88   if (rwl->nExclusiveAccessCount == 0)
     89     {
     90       if (rwl->nCompletedSharedAccessCount > 0)
     91 	{
     92 	  rwl->nSharedAccessCount -= rwl->nCompletedSharedAccessCount;
     93 	  rwl->nCompletedSharedAccessCount = 0;
     94 	}
     95 
     96       if (rwl->nSharedAccessCount > 0)
     97 	{
     98 	  if ((result =
     99 	       pthread_mutex_unlock (&(rwl->mtxSharedAccessCompleted))) != 0)
    100 	    {
    101 	      (void) pthread_mutex_unlock (&(rwl->mtxExclusiveAccess));
    102 	      return result;
    103 	    }
    104 
    105 	  if ((result =
    106 	       pthread_mutex_unlock (&(rwl->mtxExclusiveAccess))) == 0)
    107 	    {
    108 	      result = EBUSY;
    109 	    }
    110 	}
    111       else
    112 	{
    113 	  rwl->nExclusiveAccessCount = 1;
    114 	}
    115     }
    116   else
    117     {
    118       result = EBUSY;
    119     }
    120 
    121   return result;
    122 }
    123