1 files changed, 54 insertions, 108 deletions

diff --git a/pthread_once.c b/pthread_once.c
index 1c0e01f..d27b49c 100644
--- a/pthread_once.c
+++ b/pthread_once.c
@@ -41,21 +41,20 @@
 static void
 ptw32_once_init_routine_cleanup(void * arg)
 {
+  int oldCancelState;
   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);
+  (void) PTW32_INTERLOCKED_EXCHANGE((LPLONG)&once_control->done, (LONG)PTW32_ONCE_CANCELLED);
+  (void) PTW32_INTERLOCKED_EXCHANGE((LPLONG)&once_control->started, -1L);
+  /*
+   * Wake everyone up.
+   *
+   * Holding the mutex during the broadcast prevents threads being left
+   * behind waiting.
+   */
+  (void) pthread_mutex_lock(&ptw32_once_control.mtx);
+  (void) pthread_cond_broadcast(&ptw32_once_control.cond);
+  (void) pthread_mutex_unlock(&ptw32_once_control.mtx);
 }
 
 
@@ -75,11 +74,6 @@ pthread_once (pthread_once_t * once_control, void (*init_routine) (void))
 	 *      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
@@ -99,6 +93,7 @@ pthread_once (pthread_once_t * once_control, void (*init_routine) (void))
 	 */
 {
   int result;
+  int oldCancelState;
 
   if (once_control == NULL || init_routine == NULL)
     {
@@ -112,113 +107,64 @@ pthread_once (pthread_once_t * once_control, void (*init_routine) (void))
       result = 0;
     }
 
-  while (!(InterlockedExchangeAdd((LPLONG)&once_control->state, 0L) /* Atomic Read */
-	   & (LONG)PTW32_ONCE_DONE))
+  /*
+   * Use a single global cond+mutex to manage access to all once_control objects.
+   * Unlike a global mutex on it's own, the global cond+mutex allows faster
+   * once_controls to overtake slower ones. Spurious wakeups may occur, but
+   * can be tolerated.
+   *
+   * To maintain a separate mutex for each once_control object requires either
+   * cleaning up the mutex (difficult to synchronise reliably), or leaving it
+   * around forever. Since we can't make assumptions about how an application might
+   * employ pthread_once objects, the later is considered to be unacceptable.
+   *
+   * Since this is being introduced as a bug fix, the global cond+mtx also avoids
+   * a change in the ABI, maintaining backwards compatibility.
+   */
+
+  while (!InterlockedExchangeAdd((LPLONG)&once_control->done, 0L) /* Full mem barrier read */
+	 & PTW32_ONCE_DONE)
     {
-      if (!PTW32_INTERLOCKED_EXCHANGE((LPLONG)&once_control->started, (LONG)PTW32_TRUE))
+      if (PTW32_INTERLOCKED_EXCHANGE((LPLONG) &once_control->started, 0L) == -1)
 	{
-	  /*
-	   * 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.
-	       */
-	    }
+	  /* In case the previous initter was cancelled, reset cancelled state */
+	  (void) PTW32_INTERLOCKED_EXCHANGE((LPLONG)&once_control->done, (LONG)PTW32_ONCE_CLEAR);
+
+#ifdef _MSC_VER
+#pragma inline_depth(0)
+#endif
 
-	  pthread_cleanup_push(ptw32_once_init_routine_cleanup, (void *) once_control);
-	  (*init_routine)();
+	  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);
+#ifdef _MSC_VER
+#pragma inline_depth()
+#endif
 
 	  /*
-	   * we didn't create the event.
-	   * it is only there if there is someone waiting
+	   * Holding the mutex during the broadcast prevents threads being left
+	   * behind waiting.
 	   */
-	  EnterCriticalSection(&ptw32_once_event_lock);
-	  if (once_control->event)
-	    {
-	      SetEvent(once_control->event);
-	    }
-	  LeaveCriticalSection(&ptw32_once_event_lock);
+	  (void) pthread_mutex_lock(&ptw32_once_control.mtx);
+	  once_control->done = PTW32_TRUE;
+	  (void) pthread_cond_broadcast(&ptw32_once_control.cond);
+	  (void) pthread_mutex_unlock(&ptw32_once_control.mtx);
 	}
       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 */
+	  pthread_setcancelstate(PTHREAD_CANCEL_DISABLE, &oldCancelState);
+	  (void) pthread_mutex_lock(&ptw32_once_control.mtx);
+	  while (!once_control->done)
 	    {
 	      /* Neither DONE nor CANCELLED */
-	      (void) WaitForSingleObject(once_control->event, INFINITE);
+	      (void) pthread_cond_wait(&ptw32_once_control.cond, &ptw32_once_control.mtx);
 	    }
-
-	  /* 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);
+	  (void) pthread_mutex_unlock(&ptw32_once_control.mtx);
+	  pthread_setcancelstate(oldCancelState, NULL);
 	}
     }
 
-
   /*
    * Fall through Intentionally
    */