Comments on: Debugging Deadlocks – Print All Stack Traces

By: Ben Fowler

Ben Fowler — Mon, 24 Nov 2008 20:11:16 +0000

Or hit CTRL-Break on the console, but that can suck if you’ve got a big application with deep stack traces like we do. Alternatively, I seem to remember Eclipse having some fancy deadlock detection and monitor debugging stuff in their Java debugger too, although I’m not too sure how good they are for thread debugging, since I’ve only been forced to use it a couple of times.

By: Spyder

Spyder — Mon, 24 Nov 2008 13:26:54 +0000

JConsole has been the best-kept java secret on windows for years, although the JDK5 version wasn’t quite as good :)

The latest iteration (it was still jconsole in the 6u10 betas, but I haven’t looked for it since the release) is pretty darn cool – it will give you a BLOCKED status on deadlocked threads and tell you the object hashcode it is blocked on, along with the thread ID that is holding it. Makes debugging deadlocks a breeze.

It’s actually useful even without deadlocks – I’ve used it many times to generate HPROF dumps of a running JVM for debugging leaks in SAP Memory Analyser.

By: Adrian Sutton

Adrian Sutton — Mon, 24 Nov 2008 11:48:38 +0000

Odi,
Interesting, I’ll have to keep that in mind when I next get a deadlock on Windows – this one was on my Mac so Java 6 wasn’t an option (Safari is 32bit, Java 6 on Mac is 64bit only so applets only use Java 5).

I wonder if jvisualvm would affect the timing and cause the issue to not happen though? I know it’s very low overhead so it’s got a pretty good chance, but I’m not sure if it’s completely zero overhead. Seems a lot more likely to work than a debugger though.

By: Odi

Odi — Mon, 24 Nov 2008 11:41:43 +0000

You should also look into jvisualvm of JDK 1.6.0_10 (formerly jconsole). It can do that with one click and even lets you browse the heap and do some basic profiling. Stuff that you needed a good IDE for before. Quite amazing.

By: Adrian Sutton

Adrian Sutton — Mon, 24 Nov 2008 11:30:35 +0000

Oh yes, I meant to mention that but forgot, thanks for reminding me. It’s very useful but tends to be hit and miss for debugging applets – especially when you’ve deadlocked the UI thread which tends to crash the browser.

By: SteveL

SteveL — Mon, 24 Nov 2008 11:27:15 +0000

kill -QUIT does a stack dump of a JVM; on JRockit it even lists which item every thread is waiting on, which is generally all you need to identify deadlocks