How does ThreadPoolExecutor interrupt the idle threads?

Question

I just went through the source code of ThreadPoolExecutor found that it will interrupt all idle workers once the time is up to the set value of keepAliveTime and allowCoreThreadTimeOut is true.

It's a little strange to me it can only invoke the interrupt method when runState >= SHUTDOWN:

The code below is from the method getTask() of ThreadPoolExecutor.

Runnable getTask() {
...
if (workerCanExit()) {
    if (runState >= SHUTDOWN) // Wake up others
        interruptIdleWorkers();
    return null;
   }
}

Does that mean all the idle threads can only be interrupted when the runState >= SHUTDOWN (SHUTDOWN, STOP or TERMINATED)? That's to say they will be not interrupted when the state is RUNNING.

Answer 1

You are right. This getTask() method in the ThreadPoolExecutor is called on to gets the next task for a worker thread to run. This code block is only executed when the method call has not identified any Runnable task for execution. So, if nothing is found to execute, it must check for the shutdown state.

from java doc of workerCanExit()

Check whether a worker thread that fails to get a task can exit. We allow a worker thread to die if the pool is stopping, or the queue is empty, or there is at least one thread to handle possibly non-empty queue, even if core timeouts are allowed.