Java list of waiting threads

Question

Is there a way to get a list of waiting threads/number of waiting threads on an object?

Answer 1

If you are using the synchronized keyword - no. But if you are using the java.util.concurrent locks, you can.

ReentrantLock has a protected method getWaitingThreads(). If you extend it, you can make it public.

Update: You are using .wait() and .notify(), so you can manually fill and empty a List - before wach .wait() call list.add(Thread.currentThread(), and remove it before each notify. It's not perfect, but actually you shouldn't need such a list.