How to Tell if a Thread Pool is Idle in Java

Question

I have a thread pool created using ``` java.util.concurrent.ThreadPoolExecutor ``` Is there anyway I can wait till the pool is idle? By which I mean all the threads are not running and nothing is waiting in the queue. I searched the web and all the solutions don't work for me. For example, I don't want shutdown the pool so `awaitTermination()` wouldn't work. I also know how to `getTaskCount()` but I don't want keep polling the pool, which wastes CPU. This is a large project and I don't want change all the tasks running in the pool so I am looking for some solution that don't rely on task cooperation. So latches or barriers don't work for me.

Accepted Answer

You could subclass ThreadPoolExecutor and add hooks with beforeExecute and afterExecute to track task execution however you like, including basic math to count the currently executing tasks. There is also direct access to the Queue with getQueue().

Between these you can easily implement the tracking you ask for. I'm curious what your use case is... what will you do with the pool when it is empty?

How to Tell if a Thread Pool is Idle in Java

Solution

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