!15.8.2001 Strange phenomenas with Memory and Java
In our current project we have a memory consuming Calculator-Monster,
which eats up to 40 M per instance. That, of course, is not strange
phenomena with Java :), but following is: when the object is set to null (we
believe everything else related is null also), nothing significant happens with
memory. Even more strange is that when we perform System.gc() after nullifying,
the use of memory RISES (about 7M). Eventually after few load-close -operations
java runs OutOfMemory. Any ideas, questions, experiences? Anything at all is
appreciated.

--[tuomasp]

It is my understanding that an object can be both ''dead'' (= no longer has references) and still be referenced.  Typically you add an object to a Collection of some sort and then forget about it.  Or, you may have a reference to the object in Swing (by addXXXListener()).

I had once a problem with a starved thread holding references to an object that was supposedly being garbage collected.

There is an excellent article in [Doctor Dobb's Journal|http://www.ddj.com] that might be of some help. 

* [http://www.ddj.com/articles/2000/0002/0002l/0002l.htm]
* [An article describing how to use different reference types to help with memory leaks|http://www.javaworld.com/javaworld/javatips/jw-javatip79.html]

--[JanneJalkanen]

Yup, we found the bug, indeed it related to listeners. I __strongly__ recommend
above articles to everyone.

--[tuomasp]

Image 2D API has its own cache mechanism, which sometimes allocates quite
huge amounts of memory. It is usually a good idea to turn off the cache in
case you have processes that are refresing their once loaded images. The
cache would keep all old versions in its internal data structures by
default :(

--[Asser]

The DDJ article has now disappeared for non-subscribers.

-- [JeroenWenting]

We've got a quad processor machine and this made a difference...
To stop OutOfMemory errors, we used these options:
java -Xms128m -Xmx2048m -XX:+UseParallelGC=2 -XX:MaxPermSize=128m
Read up on those switches:
[http://www.wilsonmar.com/1javagc.htm#PermMemz]\\
[http://www.javaperformancetuning.com/news/qotm026.shtml]\\
--[DonRota|mailto:drrota@us.ibm.com]


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The Table of Contents plugin can cause this problem if a header symbol (!) is placed before it because it causes a recursive loop.

--richard, 14-May-2006