What are the possible reason for a java.util.concurrent.RejectedExecutionException in a SingleThreadExecutor

Question

I create the following executor in a singleton:

   final private ExecutorService executor = Executors.newSingleThreadExecutor(new ThreadFactory() {         final ThreadFactory delegate = Executors.defaultThreadFactory();         public Thread newThread(Runnable paramAnonymousRunnable) {              Thread localThread =      this.delegate.newThread(paramAnonymousRunnable);             localThread.setName("MyTask-" + localThread.getName());             localThread.setDaemon(XXX.this.daemonThread);             return localThread;         }     }); 

And during the execution of the program, there a lot call to this method of the singleton. The calls are done in different threads and maybe at the sametime.

private void send(final String paramString) {   try {       this.executor.execute(new Runnable() {           public void run() {               //DO some interesting stuff           }       });   } catch (Exception localException) {     this.handler.handle(localException);   } 

}

And at some point the following stacks start to appear:

java.util.concurrent.RejectedExecutionException         at java.util.concurrent.ThreadPoolExecutor$AbortPolicy.rejectedExecution(ThreadPoolExecutor.java:1774)         at java.util.concurrent.ThreadPoolExecutor.reject(ThreadPoolExecutor.java:768)         at java.util.concurrent.ThreadPoolExecutor.execute(ThreadPoolExecutor.java:656)         at java.util.concurrent.Executors$DelegatedExecutorService.execute(Executors.java:589)         at XXXXX.send(XXXX.java:269) 

Why the jvm will throw such exception?

The singleThreadExecutor is backed by a LinkedBlockingQueue().
And the thread pool wasn't shutdown.

for information, the jvm is oracle jdk 1.6. The singleton is created with spring. copy from java.util.concurrent.Executors:

   public static ExecutorService newSingleThreadExecutor(ThreadFactory threadFactory) {        return new FinalizableDelegatedExecutorService            (new ThreadPoolExecutor(1, 1,                                 0L, TimeUnit.MILLISECONDS,                                 new LinkedBlockingQueue<Runnable>(),                                 threadFactory));    } 

Answer 1

There are two reasons why execute would throw a RejectedExecutionException

1. The queue is full and you cannot add any more threads
2. The ThreadPool has been shutdown

Since you are using a LinkedBlockingQueue the only way I can see this occurring is because you shutdown the pool.

Answer 2

You might have submitted tasks after calling executor.shutdown(). Normally to stop executor they do

    executor.shutdown();     executor.awaitTermination(10, TimeUnit.MINUTES);