[visad] memory leak in visad

[Stuart Maclean <stuart@xxxxxxxxxxxxxxxxxx>]

I have been using visad and idv classes for offscreen rendering.  On  
long lived apps, using IDV's MapProjectionDisplay, I run out of  
memory. My apps are of  the form

new MapProejctionDisplay
add a DisplayableData
getImage
destroy


Using the  jhat heap dump analysis tool in Java6, I think I have found  
the culprit.  visad's DisplayRealType has a static vector into which  
all instances are added.  There is no method to remove instances from  
this list.  So even making sure that names of DisplayRealTypes do not  
clash, my program leaks.

I am happy to fix this locally in the source code, but am unsure of  
the implications, even within this one class.  Why must names be  
unique?  Can I just add a 'remove by name' method and call this from  
somewhere, probably MapProjectionDisplay??

I note that in ScalarType, use is made of WeakMapValues, in order to  
avoid another memory issue relating to static maps.  This idiom seems  
to have not crossed over to DisplayRealType??
It seems like DRT is almost duplicating uniqueness logic already in  
ScalarType????

Any advice appreciated

Stuart