how to generate thread dump java on out of memory error

Question

• does java 6 generate thread dump in addition to heap dump (java_pid14941.hprof)

• this is what happened to one of my applications.

  java.lang.OutOfMemoryError: GC overhead limit exceeded Dumping heap to java_pid14941.hprof ...

• I did find ava_pid14941.hprof in working directory, but didn't find any file which contains thread dump. I need to know what all the threads were doing when I got this OutOfMemory error.

• Is there any configuration option which will generate thread dump in addition to heap dump on out of memory exception?

Answer 1

I don't think there is anything in java that would provide you with on-exit thread dumps. I tackle this when necessary by having a cronjob that does periodic kill -3 pid. Yes, it does clutter the logs a bit, but the footprint is still negligible.

And if you are suffering from OOM, it might be be beneficial to see how the situation evolved thread-wise.

Answer 2

How to generate thread dump java on out of memory error?

Your question can be simplified into:

• how to generate a thread dump

and:

• how to catch an out of memory error (don't pay attention to naysayer here, they're missing the bigger picture, see my comment)

So it's actually quite easy, you could do it like this:

• install a default uncaught exception handler

• upon catching an uncaught exception, check if you have an OutOfMemoryError

• if you have an OutOfMemoryError, generate yourself a full thread dump and either ask the user to send it to you by email or offer to send it automatically

Bonus: it works fine on 1.5 too :)

 Thread.setDefaultUncaughtExceptionHandler( new Thread.UncaughtExceptionHandler() {
     public void uncaughtException( final Thread t, final Throwable e ) {
         ...
     }

You may want to look into this:

 e.getMessage();

and this:

Thread.getAllStackTraces();

I'm doing this all the time in an app that is shipped on hundreds of different 1.5 and 1.6 JVM (on different OSes).

Answer 3

If you're in a Linux/Unix environment you can do this:

-XX:OnOutOfMemoryError="kill -3 pid"

This way you don't have to have your application generate periodic thread dumps and you'll get a snapshot when it actually chokes.

Cheers,

Jim