interpreting java thread dumps

[John Turnbull]

Hi,
I'm investigating a weblogic server which is hanging when going into excess garbage collection.
I'd like to thread dump it to find out if this is caused by application code, but am having great difficulty interpretting the thread dump output.
The jvm is:

java version "1.4.2"
Java(TM) 2 Runtime Environment, Standard Edition
Fast VM (build 1.4.2-4.p2, native threads, mixed mode, 05/10/2005-02:43)

The OS is:
OSF1 V5.1 2650 alpha

While it is garbage collecting I cannot get a thread dump, so I set up a shell script to fire endless kill -3 at it. When it eventually emerges from gc I get a torrent of thread information, but it seems completely jumbled up, e.g. the string
--- dumping threads ---
appears either in repeating groups or not at all, so does not appear to be delimitting individual thread dumps.
I tried parsing the file grouping by unique threads, but I find sequences such as
thread 1
...
thread 2
...
thread 1
....
thread 3
....
thread 1

I would have expected sequences of all the threads, but this doesn't appear to be the case.

Are there any tools to make sense of the thread dump, or a description of their structure?

Thanks,
John Cattanach