/* * 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" static 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); EnterCriticalSection(&ptw32_once_event_lock); if (once_control->event) { /* * There are waiters, wake some up * We're deliberately not using PulseEvent. It's iffy, and deprecated. */ 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) /* Atomic Read */ & (LONG)PTW32_ONCE_DONE)) { 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); once_control->eventUsers++; /* * RE CANCELLATION: * 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, maybe forever; * 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). In case the old event is reused, the event is always reset by * the new initter after clearing the CANCELLED state, causing any threads that are * cycling around the loop to wait again. */ if (!once_control->event) { 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 Read */ { /* Neither DONE nor CANCELLED */ (void) WaitForSingleObject(once_control->event, INFINITE); } /* last one out shut off the lights */ EnterCriticalSection(&ptw32_once_event_lock); if (0 == --once_control->eventUsers) { /* 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 */