text: /*
   * pthread_rwlock_check_need_init.c
   *
   * Description:
   * This translation unit implements read/write lock primitives.
   *
   * --------------------------------------------------------------------------
   *
   *      Pthreads-embedded (PTE) - POSIX Threads Library for embedded systems
   *      Copyright(C) 2008 Jason Schmidlapp
   *
   *      Contact Email: jschmidlapp@users.sourceforge.net
   *
   *
   *      Based upon 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 original list of contributors to the Pthreads-win32 project
   *      is contained in the file CONTRIBUTORS.ptw32 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 <pthread.h>
  #include "implement.h"
  
  int
  pte_rwlock_check_need_init (pthread_rwlock_t * rwlock)
  {
    int result = 0;
  
    /*
     * The following guarded test is specifically for statically
     * initialised rwlocks (via PTHREAD_RWLOCK_INITIALIZER).
     *
     * Note that by not providing this synchronisation we risk
     * introducing race conditions into applications which are
     * correctly written.
     *
     * Approach
     * --------
     * We know that static rwlocks will not be PROCESS_SHARED
     * so we can serialise access to internal state using
     * critical sections rather than mutexes.
     *
     * If using a single global lock slows applications down too much,
     * multiple global locks could be created and hashed on some random
     * value associated with each mutex, the pointer perhaps. At a guess,
     * a good value for the optimal number of global locks might be
     * the number of processors + 1.
     *
     */
  
  
    pte_osMutexLock (pte_rwlock_test_init_lock);
  
    /*
     * We got here possibly under race
     * conditions. Check again inside the critical section
     * and only initialise if the rwlock is valid (not been destroyed).
     * If a static rwlock has been destroyed, the application can
     * re-initialise it only by calling pthread_rwlock_init()
     * explicitly.
     */
    if (*rwlock == PTHREAD_RWLOCK_INITIALIZER)
      {
        result = pthread_rwlock_init (rwlock, NULL);
      }
    else if (*rwlock == NULL)
      {
        /*
         * The rwlock has been destroyed while we were waiting to
         * initialise it, so the operation that caused the
         * auto-initialisation should fail.
         */
        result = EINVAL;
      }
  
    pte_osMutexUnlock(pte_rwlock_test_init_lock);
  
    return result;
  }
  