How to get the number of current worker threads in a JVM threadpool?

Question

I am using the threadpool classes in java Base class library. Specifically Executors.newFixedThreadPool() etc.

In my application i want to log metrics on how many threads are running (actually doing user supplied work) vs waiting for work.

I looked at the hooks provided by the classes, but could not find any way to do it.

I can of course implement something like that by putting my work unit in the worker thread around a try/finally and incrementing/decrementing a global counter. But was wondering if there was something out of the box that i am missing.

Answer 1

To get total number of threads:

Set<Thread> threadSet = Thread.getAllStackTraces().keySet();