Why does Executors.newCachedThreadPool throw java.util.concurrent.RejectedExecutionException during submit

Question

Number of tasks (threads) submitted is also not huge in this test scenario.

Answer 1

I dont see anywhere in the invocation of the Executors.newCachedThreadPool() methods where a RejectedExecutionException is thrown. There are only three cases where it appears to be thrown in Java 6:

• when calling execute() on a ThreadPoolExecutor and the maximum pool size has been reached.
• when calling execute() on a ThreadPoolExecutor at the same time that shutdownNow, and has essentially lost the race with the shutdownNow call.
• when trying to schedule execution of a runnable in a ScheduledThreadPoolExecutor after the executor has been shutdown.

Answer 2

You'll need to provide code samples of how you instantiate and call submit on the pool (IP should be a non-issue here as we don't need details of the internals of your Callable classes or anything like that).

Based on the information that you've given, you're almost certainly shutting down the executor service somewhere before submitting the callable to it. Check if you make any calls to shutdown or shutdownNow, and if so ensure that you're not adding tasks after this point.

Beyond that, you may want to register your own implementation of java.util.concurrent.RejectedExecutionHandler in order to aid in debugging; its [rejectedExecution][1] message will be called whenever the executor is unable to accept a task, so you could put some rudimentary state-inspection logic there to help you find the cause.

[1]: http://java.sun.com/javase/6/docs/api/java/util/concurrent/RejectedExecutionHandler.html#rejectedExecution%28java.lang.Runnable, java.util.concurrent.ThreadPoolExecutor)