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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