6796915: Deadlock in XAWT when switching virtual desktops

Reviewed-by: art, anthony

src/solaris/classes/sun/awt/X11/XDropTargetRegistry.java

@@ -534,15 +534,18 @@ final class XDropTargetRegistry {
         return entry.getSite(x, y);
     }
 
+    /*
+     * Note: this method should be called under AWT lock.
+     */
     public void registerDropSite(long window) {
+        assert XToolkit.isAWTLockHeldByCurrentThread();
+
         if (window == 0) {
             throw new IllegalArgumentException();
         }
 
         XDropTargetEventProcessor.activate();
 
-        XToolkit.awtLock();
-        try {
         long toplevel = getToplevelWindow(window);
 
         /*
@@ -570,18 +573,18 @@ final class XDropTargetRegistry {
         } else {
             registerEmbeddedDropSite(toplevel, window);
         }
-        } finally {
-            XToolkit.awtUnlock();
-        }
     }
 
+    /*
+     * Note: this method should be called under AWT lock.
+     */
     public void unregisterDropSite(long window) {
+        assert XToolkit.isAWTLockHeldByCurrentThread();
+
         if (window == 0) {
             throw new IllegalArgumentException();
         }
 
-        XToolkit.awtLock();
-        try {
         long toplevel = getToplevelWindow(window);
 
         if (toplevel == window) {
@@ -597,9 +600,6 @@ final class XDropTargetRegistry {
         } else {
             unregisterEmbeddedDropSite(toplevel, window);
         }
-        } finally {
-            XToolkit.awtUnlock();
-        }
     }
 
     public void registerXEmbedClient(long canvasWindow, long clientWindow) {

src/solaris/classes/sun/awt/X11/XWindowPeer.java

@@ -1757,9 +1757,12 @@ class XWindowPeer extends XPanelPeer implements WindowPeer,
         }
     }
 
+    // should be synchronized on awtLock
     private int dropTargetCount = 0;
 
-    public synchronized void addDropTarget() {
+    public void addDropTarget() {
+        XToolkit.awtLock();
+        try {
             if (dropTargetCount == 0) {
                 long window = getWindow();
                 if (window != 0) {
@@ -1767,9 +1770,14 @@ class XWindowPeer extends XPanelPeer implements WindowPeer,
                 }
             }
             dropTargetCount++;
+        } finally {
+            XToolkit.awtUnlock();
+        }
     }
 
-    public synchronized void removeDropTarget() {
+    public void removeDropTarget() {
+        XToolkit.awtLock();
+        try {
             dropTargetCount--;
             if (dropTargetCount == 0) {
                 long window = getWindow();
@@ -1777,6 +1785,9 @@ class XWindowPeer extends XPanelPeer implements WindowPeer,
                     XDropTargetRegistry.getRegistry().unregisterDropSite(window);
                 }
             }
+        } finally {
+            XToolkit.awtUnlock();
+        }
     }
     void addRootPropertyEventDispatcher() {
         if( rootPropertyEventDispatcher == null ) {
@@ -1838,7 +1849,9 @@ class XWindowPeer extends XPanelPeer implements WindowPeer,
         }
     }
 
-    protected synchronized void updateDropTarget() {
+    protected void updateDropTarget() {
+        XToolkit.awtLock();
+        try {
             if (dropTargetCount > 0) {
                 long window = getWindow();
                 if (window != 0) {
@@ -1846,6 +1859,9 @@ class XWindowPeer extends XPanelPeer implements WindowPeer,
                     XDropTargetRegistry.getRegistry().registerDropSite(window);
                 }
             }
+        } finally {
+            XToolkit.awtUnlock();
+        }
     }
 
     public void setGrab(boolean grab) {