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