diff options
| -rw-r--r-- | compat/win32/pthread.c | 100 | ||||
| -rw-r--r-- | compat/win32/pthread.h | 9 |
2 files changed, 94 insertions, 15 deletions
diff --git a/compat/win32/pthread.c b/compat/win32/pthread.c index 631c0a46e..5fc1670be 100644 --- a/compat/win32/pthread.c +++ b/compat/win32/pthread.c @@ -52,24 +52,38 @@ int win32_pthread_join(pthread_t *thread, void **value_ptr) int pthread_cond_init(pthread_cond_t *cond, const void *unused) { cond->waiters = 0; + cond->was_broadcast = 0; + InitializeCriticalSection(&cond->waiters_lock); cond->sema = CreateSemaphore(NULL, 0, LONG_MAX, NULL); if (!cond->sema) die("CreateSemaphore() failed"); + + cond->continue_broadcast = CreateEvent(NULL, /* security */ + FALSE, /* auto-reset */ + FALSE, /* not signaled */ + NULL); /* name */ + if (!cond->continue_broadcast) + die("CreateEvent() failed"); + return 0; } int pthread_cond_destroy(pthread_cond_t *cond) { CloseHandle(cond->sema); - cond->sema = NULL; - + CloseHandle(cond->continue_broadcast); + DeleteCriticalSection(&cond->waiters_lock); return 0; } int pthread_cond_wait(pthread_cond_t *cond, CRITICAL_SECTION *mutex) { - InterlockedIncrement(&cond->waiters); + int last_waiter; + + EnterCriticalSection(&cond->waiters_lock); + cond->waiters++; + LeaveCriticalSection(&cond->waiters_lock); /* * Unlock external mutex and wait for signal. @@ -82,22 +96,52 @@ int pthread_cond_wait(pthread_cond_t *cond, CRITICAL_SECTION *mutex) /* let's wait - ignore return value */ WaitForSingleObject(cond->sema, INFINITE); - /* we're done waiting, so make sure we decrease waiters count */ - InterlockedDecrement(&cond->waiters); - + /* + * Decrease waiters count. If we are the last waiter, then we must + * notify the broadcasting thread that it can continue. + * But if we continued due to cond_signal, we do not have to do that + * because the signaling thread knows that only one waiter continued. + */ + EnterCriticalSection(&cond->waiters_lock); + cond->waiters--; + last_waiter = cond->was_broadcast && cond->waiters == 0; + LeaveCriticalSection(&cond->waiters_lock); + + if (last_waiter) { + /* + * cond_broadcast was issued while mutex was held. This means + * that all other waiters have continued, but are contending + * for the mutex at the end of this function because the + * broadcasting thread did not leave cond_broadcast, yet. + * (This is so that it can be sure that each waiter has + * consumed exactly one slice of the semaphor.) + * The last waiter must tell the broadcasting thread that it + * can go on. + */ + SetEvent(cond->continue_broadcast); + /* + * Now we go on to contend with all other waiters for + * the mutex. Auf in den Kampf! + */ + } /* lock external mutex again */ EnterCriticalSection(mutex); return 0; } +/* + * IMPORTANT: This implementation requires that pthread_cond_signal + * is called while the mutex is held that is used in the corresponding + * pthread_cond_wait calls! + */ int pthread_cond_signal(pthread_cond_t *cond) { - /* - * Access to waiters count is atomic; see "Interlocked Variable Access" - * http://msdn.microsoft.com/en-us/library/ms684122(VS.85).aspx - */ - int have_waiters = cond->waiters > 0; + int have_waiters; + + EnterCriticalSection(&cond->waiters_lock); + have_waiters = cond->waiters > 0; + LeaveCriticalSection(&cond->waiters_lock); /* * Signal only when there are waiters @@ -108,3 +152,37 @@ int pthread_cond_signal(pthread_cond_t *cond) else return 0; } + +/* + * DOUBLY IMPORTANT: This implementation requires that pthread_cond_broadcast + * is called while the mutex is held that is used in the corresponding + * pthread_cond_wait calls! + */ +int pthread_cond_broadcast(pthread_cond_t *cond) +{ + EnterCriticalSection(&cond->waiters_lock); + + if ((cond->was_broadcast = cond->waiters > 0)) { + /* wake up all waiters */ + ReleaseSemaphore(cond->sema, cond->waiters, NULL); + LeaveCriticalSection(&cond->waiters_lock); + /* + * At this point all waiters continue. Each one takes its + * slice of the semaphor. Now it's our turn to wait: Since + * the external mutex is held, no thread can leave cond_wait, + * yet. For this reason, we can be sure that no thread gets + * a chance to eat *more* than one slice. OTOH, it means + * that the last waiter must send us a wake-up. + */ + WaitForSingleObject(cond->continue_broadcast, INFINITE); + /* + * Since the external mutex is held, no thread can enter + * cond_wait, and, hence, it is safe to reset this flag + * without cond->waiters_lock held. + */ + cond->was_broadcast = 0; + } else { + LeaveCriticalSection(&cond->waiters_lock); + } + return 0; +} diff --git a/compat/win32/pthread.h b/compat/win32/pthread.h index b8e1bcb04..c72f100f4 100644 --- a/compat/win32/pthread.h +++ b/compat/win32/pthread.h @@ -32,17 +32,18 @@ * See also: http://www.cse.wustl.edu/~schmidt/win32-cv-1.html */ typedef struct { - volatile LONG waiters; + LONG waiters; + int was_broadcast; + CRITICAL_SECTION waiters_lock; HANDLE sema; + HANDLE continue_broadcast; } pthread_cond_t; extern int pthread_cond_init(pthread_cond_t *cond, const void *unused); - extern int pthread_cond_destroy(pthread_cond_t *cond); - extern int pthread_cond_wait(pthread_cond_t *cond, CRITICAL_SECTION *mutex); - extern int pthread_cond_signal(pthread_cond_t *cond); +extern int pthread_cond_broadcast(pthread_cond_t *cond); /* * Simple thread creation implementation using pthread API |