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/*
* pthread_rwlock_check_need_init.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 "pthread.h"
#include "implement.h"
INLINE int
ptw32_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
* Win32 Critical Sections rather than Win32 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.
*
*/
EnterCriticalSection (&ptw32_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;
}
LeaveCriticalSection (&ptw32_rwlock_test_init_lock);
return result;
}
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