continued threading issues

[Stuart Maclean]

I am using visad in an offscreen mode, inside a web application 
environment (Tomcat 5.5 is container).  Yet again I am having threading 
issues in that sometimes visad appears to lock up.

I create a DisplayImplJ2D, add scalar maps, then add some data.  I then 
always call

BufferedImage bi = displayImplJ2D.getImage( true );

I note that in certain situations this call hangs.

I note that the 'true' parameter forces a retransformation and redraw of 
the 'scene'.  If I experiment with a false value, it can lead incomplete 
graphics, ie Data objects not yet drawn.

This lack of understanding of the thread model has been my most 
frustrating bugbear using Visad. As I see it, I will have one thread per 
DisplayImpl (since the VisADCanvasJ2D created for each display starts 
its own thread), plus 5 threads in the ThreadPool.  Are there any others 
?  Should I be using more calls to disableAction/enableAction and trying 
to coordinate a 'finished image' by listening for DisplayEvents of type 
FRAME_DONE?

On a somewhat related note, I am better off using one DisplayImpl 
object, at least one per 'user' (== user agent) and then toggling 
'layers' of data on and off using DataRenderers so that I get an image 
containing just one Data object drawn, or should I use a separate 
DisplayImp object for each Data object (examples of Data for my app are 
coastline, bathymetry contours, model grid contours, etc)

I am trying to build a browser based UI system with visad producing 
BufferedImages on the server which I then convert to gif/png for browser 
consumption.  If I can only track down/understand the fail-safe method 
for producing the BufferedImage objects.

I am tempted to hack the ThreadPool to create just one thread and see 
how that goes.


Any help very gratefully appreciated.

Stuart

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