Re: [visad] memory leak in visad

• To: "Stuart Maclean" <stuart@xxxxxxxxxxxxxxxxxx>, visad@xxxxxxxxxxxxxxxx
• Subject: Re: [visad] memory leak in visad
• From: "Bill Hibbard" <hiding@xxxxxxxxx>
• Date: Tue, 2 Sep 2008 16:08:06 -0500

 Hi Stuart,

The uniqueness of DisplayRealType names and ScalarType
names is because these classes are often accessed by name,
and multiple instances with the same name may have different
properties. This could cause trouble for applications.

I wrote the DisplayRealTypeVector logic, I think before Java
included WeakMapValue. I also think Steve Emmerson
probably fixed the logic in ScalarType to use WeakMapValue.
Neither Steve nor I currently work on VisAD, but if Steve is
subscribed to this list and wants to make this change that would
be great. Or if anyone else wants to do it and knows what they're
doing, that would be great too. Perhaps in cooperation with
Stuart.

One point is that every DisplayRealType is also a ScalarType
and hence the uniqueness enforcement in ScalarType should
serve for DisplayRealType. Why didn't I realize that 12 years
ago when I was writing this code? Or is there some mysterious
reason to have this seemingly redundant uniqueness test?

Another point is that DisplayRealType instances don't require
much memory, so is this a serious memory leak?

Good luck,
Bill

  ----- Original Message -----
  From: "Stuart Maclean"
  To: visad@xxxxxxxxxxxxxxxx
  Subject: [visad] memory leak in visad
  Date: Tue, 2 Sep 2008 13:20:07 -0700


  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

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