RejectedExecutionException from AsyncTask, but haven't hit limits

Why would I be getting this error message?

If the ThreadPoolExecutor is still running, you would get this error message only if you have exceeded the number of tasks that can be queued by the ThreadPoolExecutor. The only time the RejectedExecutionException is thrown is by the ThreadPoolExecutor.AbortPolicy which is the default RejectedExecutionHandler.

To quote from the javadocs:

If a request cannot be queued, a new thread is created unless this would exceed maximumPoolSize, in which case, the task will be rejected.

There is a maximum number of tasks. See this question/answer here: Is there a limit of AsyncTasks to be executed at the same time?

Here's a link for the sourcecode for AsyncTask.

private static final int CORE_POOL_SIZE = 5;
private static final int MAXIMUM_POOL_SIZE = 128;

private static final BlockingQueue<Runnable> sWorkQueue =
        new LinkedBlockingQueue<Runnable>(10);

private static final ThreadPoolExecutor sExecutor =
    new ThreadPoolExecutor(CORE_POOL_SIZE, MAXIMUM_POOL_SIZE,
        KEEP_ALIVE, TimeUnit.SECONDS, sWorkQueue, sThreadFactory);

So it looks like it starts at 5 threads, has a queue of 10. Once the queue is full it can start up to 128 threads. So it looks like you have exceeded 138 simultaneous requests.

ThreadPoolExecutor@412716b8[Running, pool size = 128, active threads = 22, queued tasks = 0, completed tasks = 1323]

Trying to catch the ThreadPoolExecutor the exact moment that it runs out of space is going to be very hard and it will quickly turn into a heisenbug in that the more you look at the ThreadPoolExecutor numbers, the more you are going to affect the synchronization of that class and therefore you might make the bug go away.

In your case, by the time you get to log the exception with the details about the TPE, the condition must have passed.

This exception also occur if your Executor call shutdown method and after that you give new Task (Runnable) for execution. Like

mThreadPoolExecutor.shutdown();
...
...
...
mThreadPoolExecutor.execute(new Runnable(){...});