Is it OK to create multiple threadpools (ExecutorService)?

Question

I created multiple ExecutorService instances in my code, usually each UI page has one ExecutorService instance. Each ExecutorService instance will execute some http get request threads.

private ExecutorService m_threadPool = Executors.newCachedThreadPool();

Is it OK to do that?

The problem I met is that sometimes the http get requests got response code -1 from HttpURLConnection getResponseCode() call. I don't know whether it is caused by multiple threadpool instances.

Thanks.

Answer 1

It shouldn't be caused by your thread pool instances. However, I'd say that having more than one thread pool is questionable. Why would you need it? It could lead to a lot of unnecessary threads, and thereby unnecessary memory use.

Answer 2

ExecutorService per se is just another object so there's no big overhead. But each thread pool comes with a number of idle threads by default and those are a cause of a major resource waste. I would suggest setting the default number of pre-generated threads in each pool small (1 or 0 if you are not sure whether any requests are sent) in order to reduce the cost of creating extra objects. Threads would be created on demand and you'll be able to keep your code clean.

Another solution is to use a single thread pool but to maintain a separate list of tasks for each UI window. In this case when window gets closed you'll have to iterate over all tasks and cancell the running ones manually (this can also be done in a separate thread). A task may be represented by a Future<?> (it has handy isDone() and cancel() methods).