With a Java ExecutorService, how do I complete actively executing tasks but halt the processing of w

如何让正在执行的任务执行完，等待执行的任务全部取消？

I want something in between these two options.

I want to call a command that:

a. Completes the currently active task or tasks (like

shutdown

).

b. Halts the processing of waiting tasks (like

shutdownNow

).

I ran into this issue recently. There may be a more elegant approach, but my solution is to first call

shutdown()

,
then pull out the

BlockingQueue

being
used by the

ThreadPoolExecutor

and
call

clear()

on
it (or else drain it to another

Collection

for
storage). Finally, calling

awaitTermination()

allows
the thread pool to finish what's currently on its plate.

For example:

public static void shutdownPool(boolean awaitTermination) throws InterruptedException {

//call shutdown to prevent new tasks from being submitted
executor.shutdown();

//get a reference to the Queue
final BlockingQueue<Runnable> blockingQueue = executor.getQueue();

//clear the Queue
blockingQueue.clear();
//or else copy its contents here with a while loop and remove()

//wait for active tasks to be completed
if (awaitTermination) {
executor.awaitTermination(SHUTDOWN_TIMEOUT, TimeUnit.SECONDS);
}}

This method would be implemented in the directing class wrapping the

ThreadPoolExecutor

with
the reference

executor

.

It's important to note the following from the

ThreadPoolExecutor.getQueue()

javadoc:

Access to the task queue is intended primarily for debugging and monitoring. This queue may be in active use. Retrieving the task queue does not prevent queued tasks from executing.

This highlights the fact that additional tasks may be polled from the

BlockingQueue

while
you drain it. However, all

BlockingQueue

implementations
are thread-safe according to that interface's
documentation, so this shouldn't cause problems.