Many threads waiting to lock an object, but no thread is holding that lock

Question

I have an application which is currently stuck and I'm trying to understand why. In the kill -3 (thread dump) output, I see many threads waiting to lock an object (specifically - waiting on a synchronized method of Vector), but I don't see any thread holding that lock.

Any idea how can this be debugged?

Thanks

P.S. I know Vector is old and ArrayList is more recommended, but this is a legacy code which I'm trying to debug.

Answer 1

The situation you describe sounds like a classic case of deadlock.

You could (perhaps should) an IDE such as Eclipse or IntelliJ Idea, through which you could debug your application step-by-step and understand exactly where it stops and what to do.

Alternatively, pasting some code would help clarifying the situation as well as describing your environment in terms of JVM version etc.