src/java.desktop/macosx/native/libawt_lwawt/awt/LWCToolkit.m

@@ -1,7 +1,7 @@
 /*
- * Copyright (c) 2011, 2019, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2011, 2020, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
  * under the terms of the GNU General Public License version 2 only, as
  * published by the Free Software Foundation.  Oracle designates this

@@ -68,17 +68,34 @@
 static pthread_cond_t sAppKitStarted_cv = PTHREAD_COND_INITIALIZER;
 
 @implementation AWTToolkit
 
 static long eventCount;
+static BOOL inDoDragDropLoop;
+
++ (BOOL) inDoDragDropLoop {
+  @synchronized(self) {
+    return inDoDragDropLoop;
+  }
+}
+
++ (void) setInDoDragDropLoop:(BOOL)val {
+  @synchronized(self) {
+    inDoDragDropLoop = val;
+  }
+}
 
 + (long) getEventCount{
+  @synchronized(self) {
     return eventCount;
+  }
 }
 
 + (void) eventCountPlusPlus{
+  @synchronized(self) {
     eventCount++;
+  }
 }
 
 + (jint) scrollStateWithEvent: (NSEvent*) event {
 
     if ([event type] != NSScrollWheel) {

@@ -418,14 +435,20 @@
         //  - CGEventPost(), see CRobot.m
         // It was found that if we post an event via CGEventPost in robot and
         // immediately after this we will post the second event via
         // [NSApp postEvent] then sometimes the second event will be handled
         // first. The opposite isn't proved, but we use both here to be safer.
+
+        // If the native drag is in progress, skip native sync.
+        if (!AWTToolkit.inDoDragDropLoop) {
         [theApp postDummyEvent:false];
         [theApp waitForDummyEvent:timeout / 2.0];
+        }
+        if (!AWTToolkit.inDoDragDropLoop) {
         [theApp postDummyEvent:true];
         [theApp waitForDummyEvent:timeout / 2.0];
+        }
 
     } else {
         // could happen if we are embedded inside SWT application,
         // in this case just spin a single empty block through
         // the event loop to give it a chance to process pending events