"Refreshing" a fixed size thread pool when using for a ExecutorService

Question

In my application, I use ExecutorService a lot for making async calls.

ExecutorService executorService = Executors.newFixedThreadPool(10);

And I shutdown the executorService only when the app (web based) shuts down. Recently when debugging some issues I was looking through this code and wondering whether there can be cases during the execution of the program when I am forced to shutdown the ExecutorService and restart it i.e. new set of pooled threads. So I wanted to know what typical scenarios/unexpected application behavior can force me to do so?

The typical exceptions that I check for are ExecutionException, InterruptedException, CancellationException but I don't do much apart from logging them.

Answer 1

The general answer is that you shouldn't have to recycle the pool; it's designed to minimize your need to do that. The two cases you might consider are:

• An abrupt unhandled exception in one of your tasks. In this case, the task will fail (and you have the option of catching unhandled exceptions via the thread pool hooks, or a UncaughtExceptionHandler) and the worker thread may exit. However, the thread pool handles this cleanly, and the next request into the thread pool will create a replacement if need be.

• A worker thread deadlocks. This one is not so easy to predict or detect -- I can't imagine structuring an application around recycling a thread pool to cope with deadlocked worker threads.

Apart from these two edge conditions, I see no reason to worry about periodic cycling to a new thread pool.

Some folks do create and destroy thread pools because they aren't aware of the CompletionService, convenience methods like invokeAll(), and the flexibility of monitoring completion with Futures.