/*
 * pthread_rwlock_rdlock.c
 *
 * Description:
 * This translation unit implements read/write lock primitives.
 *
 * --------------------------------------------------------------------------
 *
 *      Pthreads4w - POSIX Threads Library for Win32
 *      Copyright(C) 1998 John E. Bossom
 *      Copyright(C) 1999-2018, Pthreads4w contributors
 *
 *      Homepage: https://sourceforge.net/projects/pthreads4w/
 *
 *      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:
 *      https://sourceforge.net/p/pthreads4w/wiki/Contributors/
 *
 * This file is part of Pthreads4w.
 *
 *    Pthreads4w is free software: you can redistribute it and/or modify
 *    it under the terms of the GNU General Public License as published by
 *    the Free Software Foundation, either version 3 of the License, or
 *    (at your option) any later version.
 *
 *    Pthreads4w 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 General Public License for more details.
 *
 *    You should have received a copy of the GNU General Public License
 *    along with Pthreads4w.  If not, see <http://www.gnu.org/licenses/>. *
 */

#ifdef HAVE_CONFIG_H
# include <config.h>
#endif

#include <limits.h>

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

int
pthread_rwlock_rdlock (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_lock (&(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)));
}