/*
 * pthread_rwlock_tryrdlock.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) 1999,2005 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 "ptw32pch.h"

// FIXME : This function can return EBUSY when the rwlock is available for reading.
// How?  Because it uses a single "mtxExclusiveAccess" lock to wrangle control of the
// RwLock's internals -- so if two read locks are attempted in parallel, this function
// will falsely report the lock as being busy even though both locks should be allowed
// access to the object.
//
// (note: double check this against OpenGroup behavior definitions -- though even if
//  OpenGroup 'allows' this behavior, we should probably strive to avoid it unless
//  it's explicitly "expected", since programs would typically have much more desirable
//  behavior if simultaneous read locks do not EBUSY.)

int
pthread_rwlock_tryrdlock (pthread_rwlock_t * rwlock)
{
  int result;
  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 (++rwl->nSharedAccessCount == INT_MAX)
    {
      if ((result =
	   pthread_mutex_lock (&(rwl->mtxSharedAccessCompleted))) != 0)
	{
	  (void) pthread_mutex_unlock (&(rwl->mtxExclusiveAccess));
	  return result;
	}

      rwl->nSharedAccessCount -= rwl->nCompletedSharedAccessCount;
      rwl->nCompletedSharedAccessCount = 0;

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

  return (pthread_mutex_unlock (&rwl->mtxExclusiveAccess));
}