/*
 * pthread_rwlock_trywrlock.c
 *
 * Description:
 * This translation unit implements read/write lock primitives.
 *
 * --------------------------------------------------------------------------
 *
 *      Pthreads-win32 - POSIX Threads Library for Win32
 *      Copyright(C) 1998 John E. Bossom
 *      Copyright(C) 1999,2003 Pthreads-win32 contributors
 * 
 *      Contact Email: rpj@callisto.canberra.edu.au
 * 
 *      The current list of contributors is contained
 *      in the file CONTRIBUTORS included with the source
 *      code distribution. The list can also be seen at the
 *      following World Wide Web location:
 *      http://sources.redhat.com/pthreads-win32/contributors.html
 * 
 *      This library is free software; you can redistribute it and/or
 *      modify it under the terms of the GNU Lesser General Public
 *      License as published by the Free Software Foundation; either
 *      version 2 of the License, or (at your option) any later version.
 * 
 *      This library is distributed in the hope that it will be useful,
 *      but WITHOUT ANY WARRANTY; without even the implied warranty of
 *      MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 *      Lesser General Public License for more details.
 * 
 *      You should have received a copy of the GNU Lesser General Public
 *      License along with this library in the file COPYING.LIB;
 *      if not, write to the Free Software Foundation, Inc.,
 *      59 Temple Place - Suite 330, Boston, MA 02111-1307, USA
 */

#include <errno.h>
#include <limits.h>

#include "pthread.h"
#include "implement.h"

int
pthread_rwlock_trywrlock(pthread_rwlock_t * rwlock)
{
    int result, result1;
    pthread_rwlock_t rwl;

    if (rwlock == NULL || *rwlock == NULL)
      {
	return EINVAL;
      }

    /*
     * We do a quick check to see if we need to do more work
     * to initialise a static rwlock. We check
     * again inside the guarded section of ptw32_rwlock_check_need_init()
     * to avoid race conditions.
     */
    if (*rwlock == PTHREAD_RWLOCK_INITIALIZER)
      {
	result = ptw32_rwlock_check_need_init(rwlock);

	if (result != 0 && result != EBUSY)
	  {
	    return result;
	  }
      }

    rwl = *rwlock;

    if (rwl->nMagic != PTW32_RWLOCK_MAGIC)
      {
	return EINVAL;
      }

    if ((result = pthread_mutex_trylock(&(rwl->mtxExclusiveAccess))) != 0)
      {
	return result;
      }

    if ((result = pthread_mutex_trylock(&(rwl->mtxSharedAccessCompleted))) != 0)
      {
	result1 = pthread_mutex_unlock(&(rwl->mtxExclusiveAccess));
	return ((result1 != 0) ? result1 : result);
      }

    if (rwl->nExclusiveAccessCount == 0) 
      {
	if (rwl->nCompletedSharedAccessCount > 0) 
	  {
	    rwl->nSharedAccessCount -= rwl->nCompletedSharedAccessCount;
	    rwl->nCompletedSharedAccessCount = 0;
	  }

	if (rwl->nSharedAccessCount > 0) 
	  {
	    if ((result = pthread_mutex_unlock(&(rwl->mtxSharedAccessCompleted))) != 0)
	      {
		(void) pthread_mutex_unlock(&(rwl->mtxExclusiveAccess));
		return result;
	      }

	    if ((result = pthread_mutex_unlock(&(rwl->mtxExclusiveAccess))) == 0)
	      {
		result = EBUSY;
	      }
	  }
	else
	  {
	    rwl->nExclusiveAccessCount = 1;
	  }
      }
    else 
      {
	result = EBUSY;
      }

    return result;
}
