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/*
* pthread_once.c
*
* Description:
* This translation unit implements miscellaneous thread functions.
*
* --------------------------------------------------------------------------
*
* 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 "pthread.h"
#include "implement.h"
void ptw32_once_init_routine_cleanup(void * arg)
{
pthread_once_t * once_control = (pthread_once_t *) arg;
(void) PTW32_INTERLOCKED_EXCHANGE((LPLONG)&once_control->state, (LONG)PTW32_ONCE_CANCELLED);
(void) PTW32_INTERLOCKED_EXCHANGE((LPLONG)&once_control->started, (LONG)PTW32_FALSE);
// There are waiters, wake some up
// We're deliberately not using PulseEvent. It's iffy, and deprecated.
EnterCriticalSection(&ptw32_once_event_lock);
if (once_control->event)
SetEvent(once_control->event);
LeaveCriticalSection(&ptw32_once_event_lock);
}
int
pthread_once (pthread_once_t * once_control, void (*init_routine) (void))
/*
* ------------------------------------------------------
* DOCPUBLIC
* If any thread in a process with a once_control parameter
* makes a call to pthread_once(), the first call will summon
* the init_routine(), but subsequent calls will not. The
* once_control parameter determines whether the associated
* initialization routine has been called. The init_routine()
* is complete upon return of pthread_once().
* This function guarantees that one and only one thread
* executes the initialization routine, init_routine when
* access is controlled by the pthread_once_t control
* key.
*
* pthread_once() is not a cancelation point, but the init_routine
* can be. If it's cancelled then the effect on the once_control is
* as if pthread_once had never been entered.
*
*
* PARAMETERS
* once_control
* pointer to an instance of pthread_once_t
*
* init_routine
* pointer to an initialization routine
*
*
* DESCRIPTION
* See above.
*
* RESULTS
* 0 success,
* EINVAL once_control or init_routine is NULL
*
* ------------------------------------------------------
*/
{
int result;
if (once_control == NULL || init_routine == NULL)
{
result = EINVAL;
goto FAIL0;
}
else
{
result = 0;
}
while (!(InterlockedExchangeAdd((LPLONG)&once_control->state, 0L) & (LONG)PTW32_ONCE_DONE)) // Atomic Read
{
if (!PTW32_INTERLOCKED_EXCHANGE((LPLONG)&once_control->started, (LONG)PTW32_TRUE))
{
// Clear residual state from a cancelled init_routine
// (and DONE still hasn't been set of course).
if (PTW32_INTERLOCKED_EXCHANGE((LPLONG)&once_control->state, (LONG)PTW32_ONCE_CLEAR)
& PTW32_ONCE_CANCELLED)
{
// The previous initter was cancelled.
// We now have a new initter (us) and we need to make the rest wait again.
EnterCriticalSection(&ptw32_once_event_lock);
if (once_control->event)
ResetEvent(once_control->event);
LeaveCriticalSection(&ptw32_once_event_lock);
/*
* Any threads entering the wait section and getting out again before
* the CANCELLED state can be cleared and the event is reset will, at worst, just go
* around again or, if they suspend and we (the initter) completes before they resume,
* they will see state == DONE and leave immediately.
*/
}
pthread_cleanup_push(ptw32_once_init_routine_cleanup, (void *) once_control);
(*init_routine)();
pthread_cleanup_pop(0);
(void) PTW32_INTERLOCKED_EXCHANGE((LPLONG)&once_control->state, (LONG)PTW32_ONCE_DONE);
// we didn't create the event.
// it is only there if there is someone waiting
EnterCriticalSection(&ptw32_once_event_lock);
if (once_control->event)
SetEvent(once_control->event);
LeaveCriticalSection(&ptw32_once_event_lock);
}
else
{
// wait for init.
// while waiting, create an event to wait on
EnterCriticalSection(&ptw32_once_event_lock);
(void) InterlockedIncrement((LPLONG)&once_control->eventUsers);
/*
* If we are the first thread after the initter thread, and the init_routine is cancelled
* while we're suspended at this point in the code:-
* - state will not get set to PTW32_ONCE_DONE;
* - cleanup will not see an event and cannot set it;
* - therefore, we will eventually resume, create an event and wait on it;
* Remedy: cleanup must set state == CANCELLED before checking for an event, so that
* we will see it and avoid waiting (as for state == DONE). We will go around again and
* we may become the initter.
* If we are still the only other thread when we get to the end of this block, we will
* have closed the event (good). If another thread beats us to be initter, then we will
* re-enter here (good). If, when we reach lights out, other threads have reached this
* point, we will not close the event. The eventUsers counter will still correctly reflect
* the real number of waiters, the old event will remain in use. It will be reset
* by the new initter after clearing the CANCELLED state, causing any threads that are
* cycling around the loop to wait again.
*/
if (!InterlockedExchangeAdd((LPLONG)&once_control->event, 0L)) // Atomic Read
{
once_control->event = CreateEvent(NULL, PTW32_TRUE, PTW32_FALSE, NULL);
}
LeaveCriticalSection(&ptw32_once_event_lock);
// check 'state' again in case the initting thread has finished or cancelled
// and left before seeing that there was an event to trigger.
// (Now that the event IS created, if init gets finished AFTER this,
// then the event handle is guaranteed to be seen and triggered).
if (!InterlockedExchangeAdd((LPLONG)&once_control->state, 0L)) // Atomic Reads
{
// Neither DONE nor CANCELLED
(void) WaitForSingleObject(once_control->event, INFINITE);
}
// last one out shut off the lights:
EnterCriticalSection(&ptw32_once_event_lock);
if (InterlockedDecrement((LPLONG)&once_control->eventUsers) == 0) // we were last
{
CloseHandle(once_control->event);
once_control->event = 0;
}
LeaveCriticalSection(&ptw32_once_event_lock);
}
}
/*
* Fall through Intentionally
*/
/*
* ------------
* Failure Code
* ------------
*/
FAIL0:
return (result);
} /* pthread_once */
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