Cleaning up JSVGCanvas Memory

[Peter Wagener <pe...@hypoluxo.com>]

Hi All,

I've recently updated my application from using the released Batik  
1.6 to a nightly build (from a week ago or so).  Most things work  
well, and it cleared up one of my more annoying issues:  previously  
having more than one JSVGCanvas instance would consistently render  
the document off-center... the nightly build apparently fixed that  
for me.

The only issue I'm having now is with cleaning up my JSVGCanvas  
instances when I want to release all the memory associated with  
them.  Here is the code I was using with the 1.6 release; my custom  
extension of JSVGCanvas includes these methods:

<code>
     void destroyCanvas() {
         ToolTipManager ttipman = ToolTipManager.sharedInstance();
         ttipman.unregisterComponent(this);
         releaseRenderingReferences();

         stopProcessing();
         removeUpdateManager();

         removeAllNodes();
         removeAll();

         bridgeContext = null;
         listener = null;
         listenerList = null;
     }

     private void removeUpdateManager() {
         if (updateManager != null) {
             updateManager.getBridgeContext().dispose();
             updateManager = null;
         }
     }

     private void removeAllNodes() {

         SVGDocument document = getSVGDocument();
         if (document != null) {
             SVGSVGElement s = document.getRootElement();
             removeNodes(s);
         }

         System.gc();
     }

     private void removeNodes(Node n) {
         Node childNode;
         Node prevChildNode;

         for (childNode = n.getLastChild(); childNode != null;) {
             if (childNode.hasChildNodes()) {
                 removeNodes(childNode);
             }
             prevChildNode = childNode.getPreviousSibling();
             if (!(childNode instanceof SVGOMPathElement)) {
                 n.removeChild(childNode);
             }

             childNode = prevChildNode;
         }
     }
</code>


The updated nightly code, however, hits a NullPointerException when  
attempting to fire an event listener after removing a child node:

java.lang.NullPointerException
	at org.apache.batik.dom.events.EventSupport.fireEventListeners 
(Unknown Source)
	at org.apache.batik.dom.events.EventSupport.fireEventListeners 
(Unknown Source)
	at org.apache.batik.dom.events.EventSupport.dispatchEvent(Unknown  
Source)
	at org.apache.batik.dom.AbstractNode.dispatchEvent(Unknown Source)
	at org.apache.batik.dom.AbstractParentNode.fireDOMNodeRemovedEvent 
(Unknown Source)
	at org.apache.batik.dom.AbstractParentNode.removeChild(Unknown Source)
	at com.W7Optics.AppClient.LMSView.shelf.ShelfViewCanvas.removeNodes 
(ShelfViewCanvas.java:71)
	at  
com.W7Optics.AppClient.LMSView.shelf.ShelfViewCanvas.removeAllNodes 
(ShelfViewCanvas.java:55)
	at com.W7Optics.AppClient.LMSView.shelf.ShelfViewCanvas.destroyCanvas 
(ShelfViewCanvas.java:35)
         ....

Interestingly, this only happens with the second instance of  
JSVGCanvas -- the first instance appears to clean itself up just  
fine.  Before I go hopping through the code myself, does anyone have  
any suggestions?


Many Thanks,

Peter

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Re: Cleaning up JSVGCanvas Memory

[th...@kodak.com]

Hi Peter,

Peter Wagener <pe...@hypoluxo.com> wrote on 06/02/2006 06:42:52 
PM:

> I've recently updated my application from using the released Batik 
> 1.6 to a nightly build (from a week ago or so).  Most things work 
> well, and it cleared up one of my more annoying issues:  previously 
> having more than one JSVGCanvas instance would consistently render 
> the document off-center... the nightly build apparently fixed that 
> for me.

   Are you using 'trunk' of the svg11 branch.

> The only issue I'm having now is with cleaning up my JSVGCanvas 
> instances when I want to release all the memory associated with 
> them.  Here is the code I was using with the 1.6 release; my custom 
> extension of JSVGCanvas includes these methods:

   I think I've mentioned this before but I seriously question 
the need to do all this.

> The updated nightly code, however, hits a NullPointerException when 
> attempting to fire an event listener after removing a child node:

   It looks like you are using trunk.  This has come nice new
features (sXBL) and will be the future of Batik but svg11 is
currently more stable.

> java.lang.NullPointerException
>    at org.apache.batik.dom.events.EventSupport.fireEventListeners 
> (Unknown Source)

   It's a little hard to see what is causing this, line numbers
would help.  You can get line numbers by adding a file called
build.properties with the line "debug=on" next to the build.xml
file at the top of the batik build tree.

> Interestingly, this only happens with the second instance of 
> JSVGCanvas -- the first instance appears to clean itself up just 
> fine.  Before I go hopping through the code myself, does anyone have 
> any suggestions?


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