Re: [OpenMap Users] Location threading problem with DeclutterMatrix.getGraphics()?

From: Don Dietrick <dietrick_at_bbn.com>
Date: Tue, 29 Jan 2008 19:26:21 -0500

Thanks Carsten, I'll incorporate this tonight.

Best Regards,

- Don


On Jan 21, 2008, at 7:30 AM, Carsten . Madsen wrote:

> This fixes the problem
>
> ...
> /**
> * Added this to work around problem with multi threaded calls to
> * DeclutterMatrix.getGraphics.
> *
> * Replaced all calls to DeclutterMatrix.getGraphics with
> getGraphics. This
> * does have a performance impact!
> *
> * _at_see DeclutterMatrix
> *
> */
> private static class ThreadGraphicsDispenser extends ThreadLocal {
> _at_Override
> public Object initialValue() {
> BufferedImage bi = new BufferedImage(1, 1,
> BufferedImage.TYPE_INT_RGB);
> GraphicsEnvironment ge = GraphicsEnvironment
> .getLocalGraphicsEnvironment();
> Graphics2D workingGraphics = ge.createGraphics(bi);
> return workingGraphics;
> }
> }
>
> private static ThreadGraphicsDispenser graphicsDispencer = new
> ThreadGraphicsDispenser();
>
> public static Graphics2D getGraphics() {
> return (Graphics2D) graphicsDispencer.get();
> }
> ...
>
> BR
> Carsten
>
>
> Carsten . Madsen wrote:
>> Hello
>>
>> I'm running an OM app with multiple location layers on a quad core
>> box and I get the following exception on a regular basis:
>>
>> Exception in thread "Thread-64" java.lang.NullPointerException
>> at com.bbn.openmap.layer.location.Location.generate(Location.java:
>> 572)
>> ...
>> at com.bbn.openmap.layer.location.LocationLayer
>> $LocationWorker.construct(LocationLayer.java:176)
>> at com.bbn.openmap.util.SwingWorker$2.run(SwingWorker.java:116)
>> at java.lang.Thread.run(Thread.java:619)
>>
>> The Location.generate() code goes like this:
>>
>> public boolean generate(Projection proj) {
>> if (label != null) {
>> label.setY(origYLabelOffset);
>> label.setX(origXLabelOffset);
>> }
>>
>> java.awt.Graphics g = DeclutterMatrix.getGraphics();
>> if (g != null && label != null) {
>> g.setFont(label.getFont());
>> // Now set the vertical offset to the original place based
>> // off the height of the label, so that the location place
>> // is halfway up the text. That way, it looks like a
>> // label.
>> int height = g.getFontMetrics().getAscent(); // line 571
>> currentFontDescent = g.getFontMetrics().getDescent();
>> ....
>>
>>
>> as LocationLayer uses a LocationWorker (thread) to run prepare and
>> DeclutterMatrix.getGraphics() returns a static Graphics I assume
>> the exception is caused by multiple threads simultaneously
>> accessing the single graphics instance returned by
>> DeclutterMatrix.getGraphics. As the location layers stop responding
>> after the exception this rather problematic.
>>
>> As far as I can tell this is a general problem when having multiple
>> LocationLayers running on a multi core box?
>>
>> BR
>> Carsten
>>
>>
>> --
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>
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=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
Don Dietrick, dietrick_at_bbn.com
BBN Technologies, Cambridge MA
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=



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Received on Tue Jan 29 2008 - 19:26:45 EST

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