How to find CPU-intensive class in Java?

问题:

I have a big program in Java that uses multithreading. In some cases, the program starts using 100% of three cores of my eight core system. In normal use, the program use all cores at 1-2%. How can I find the class that's overloading cores?

回答1:

Use a profiler such as the jvisualvm that is bundled with jdk-1.6.0_10

回答2:

The best solution is to use a profiler - that's what they're built for, and there's a great one bundled with Java 6.

Another (far from being as ideal a solution) is to run your program in the Eclipse IDE (if that's what you use) in debug mode. You can then look at the running threads. IF a lot of them are suspended, the one that is not might be your culprit. Force it to break (from the toolbar) and you can see where it is. There are many chances that you'll find a clear loop or busy waiting.

回答3:

Use a profiler to figure out which thread(s) are using all of your CPU cycles, and the method(s) they are executing.

回答4:

If you are using Eclipse, you can use the TPTP profiling tool.

回答5:

If you are going the commercial profiler route then I would recommend using Dynatrace.

回答6:

Try taking threads dump (see jps, jstack commands) and then see which methods are executed.

回答7:

If you are using Java over UNIX or some versions of Linux look into DTrace with Java.