ThreaPool with LinkedBlockingQueue reject task when queue is empty

Question

I created a thread pool with following code

ThreadPoolExecutor backgroupTaskPool = new ThreadPoolExecutor(100, 100, 10, TimeUnit.SECONDS,  new LinkedBlockingQueue<Runnable>(100));
backgroupTaskPool.allowCoreThreadTimeOut(true);

when submit tasks to this pool, it throws RejectedExecutionException, but the threads in the pool not reaches maximumPoolSize and the LinkedBlockingQueue is empty:

Caused by: java.util.concurrent.RejectedExecutionException: Task java.util.concurrent.FutureTask@15e9aebd rejected from java.util.concurrent.ThreadPoolExecutor@7774348b[Shutting down, pool size = 9, active threads = 9, queued tasks = 0, completed tasks = 105]
    at java.util.concurrent.ThreadPoolExecutor$AbortPolicy.rejectedExecution(ThreadPoolExecutor.java:2048)
    at java.util.concurrent.ThreadPoolExecutor.reject(ThreadPoolExecutor.java:821)

Do you have any idea why could this happen?

THX.

Answer 1

Based on the exception message

Task java.util.concurrent.FutureTask@15e9aebd rejected from java.util.concurrent.ThreadPoolExecutor@7774348b[Shutting down, pool size = 9, active threads = 9, queued tasks = 0, completed tasks = 105]

You seem to be shutting down the ThreadPoolExecutor. You can't submit tasks after you've called shutdown.