multithreading - 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.