7177040: Deadlock between PostEventQueue.noEvents, EventQueue.isDispatchThread and SwingUtilities.invokeLater

Reviewed-by: anthony, ant

jdk/src/share/classes/sun/awt/SunToolkit.java

@@ -2112,27 +2112,43 @@ class PostEventQueue {
     private EventQueueItem queueTail = null;
     private final EventQueue eventQueue;
 
+    // For the case when queue is cleared but events are not posted
+    private volatile boolean isFlushing = false;
+
     PostEventQueue(EventQueue eq) {
         eventQueue = eq;
     }
 
     public synchronized boolean noEvents() {
-        return queueHead == null;
+        return queueHead == null && !isFlushing;
     }
 
     /*
      * Continually post pending AWTEvents to the Java EventQueue. The method
      * is synchronized to ensure the flush is completed before a new event
      * can be posted to this queue.
+     *
+     * 7177040: The method couldn't be wholly synchronized because of calls
+     * of EventQueue.postEvent() that uses pushPopLock, otherwise it could
+     * potentially lead to deadlock
      */
-    public synchronized void flush() {
-        EventQueueItem tempQueue = queueHead;
+    public void flush() {
+        EventQueueItem tempQueue;
+        synchronized (this) {
+            tempQueue = queueHead;
             queueHead = queueTail = null;
+            isFlushing = true;
+        }
+        try {
             while (tempQueue != null) {
                 eventQueue.postEvent(tempQueue.event);
                 tempQueue = tempQueue.next;
             }
         }
+        finally {
+            isFlushing = false;
+        }
+    }
 
     /*
      * Enqueue an AWTEvent to be posted to the Java EventQueue.