[cp-patches] FYI: LightweightDispatcher fix

[Roman Kennke]

This fixes a problem in the lightweight dispatcher, when it dispatches
events for no-more showing components. This lead to occasional glitches
in Swing GUIs.

2007-09-21  Roman Kennke  <[EMAIL PROTECTED]>

        * java/awt/LightweightDispatcher.java
        (dispatchEvent): Lock the component's tree to avoid threading
        problems.
        (redispatch): Only redispatch when component is showing.

/Roman

-- 
Dipl.-Inform. (FH) Roman Kennke, Software Engineer, http://kennke.org
aicas Allerton Interworks Computer Automated Systems GmbH
Haid-und-Neu-Straße 18 * D-76131 Karlsruhe * Germany
http://www.aicas.com   * Tel: +49-721-663 968-0
USt-Id: DE216375633, Handelsregister HRB 109481, AG Karlsruhe
Geschäftsführer: Dr. James J. Hunt

Index: java/awt/LightweightDispatcher.java
===================================================================
RCS file: /cvsroot/classpath/classpath/java/awt/LightweightDispatcher.java,v
retrieving revision 1.17
diff -u -1 -0 -r1.17 LightweightDispatcher.java
--- java/awt/LightweightDispatcher.java	10 Oct 2006 15:29:04 -0000	1.17
+++ java/awt/LightweightDispatcher.java	21 Sep 2007 08:37:49 -0000
@@ -105,21 +105,29 @@
   /**
    * Receives notification if a mouse event passes along the eventqueue.
    *
    * @param event the event
    */
   public boolean dispatchEvent(final AWTEvent event)
   {
     if (event instanceof MouseEvent)
       {
         MouseEvent mouseEvent = (MouseEvent) event;
-        return handleMouseEvent(mouseEvent);
+        /**
+         * The lightweight dispatching relies on the integrity of the
+         * component tree (e.g. isShowing(), getLocationOnScreen(), etc),
+         * therefore we must synchronize on the tree lock here.
+         */
+        synchronized (mouseEvent.getComponent().getTreeLock())
+          {
+            return handleMouseEvent(mouseEvent);
+          }
       }
     return false;
   }
 
   /**
    * Handles all mouse events that are targetted at toplevel containers
    * (Window instances) and dispatches them to the correct lightweight child.
    * 
    * @param ev the mouse event
    * @return whether or not we found a lightweight that handled the event.
@@ -279,21 +287,22 @@
    * Redispatches the specified mouse event to the specified target with the
    * specified id.
    *
    * @param ev the mouse event
    * @param target the new target
    * @param id the new id
    */
   private void redispatch(MouseEvent ev, Component target, int id)
   {
     Component source = ev.getComponent();
-    if (target != null)
+    assert target != null;
+    if (target.isShowing())
       {
         // Translate coordinates.
         int x = ev.getX();
         int y = ev.getY();
         for (Component c = target; c != null && c != source; c = c.getParent())
           {
             x -= c.x;
             y -= c.y;
           }