Question

I’m running a networking service in android where I direct all my http requests to run and get callbacks from the service when the requests are complete. I run the requests in a ThreadPoolExecutor to limit the number of concurrent requests. As the requests run within the pool, they eventually create an HttpGet or HttpPost, both of which indirectly implement AbortableHttpRequest, which allows one to cancel the connection (say, if it’s blocking for a long time).

If a user cancels a request, I’d like to somehow drill into the thread queue and call the abort routine for that request. If, for example, a web site is not responding and the user chooses to do something else, right now my only option is to wait for the standard 5 minute http timeout to occur for that hung request before that thread is freed up. If I could access the thread that has my request and call abort, that would free things up right away.

From what I can understand, it appears once my request has gone into the thread pool, it’s a black box until it comes out the other end. Querying the queue will only hand back futures, which hides the runnable.

Is there a better approach for this? I’m fairly new to java and threading (I mostly do perl, which doesn’t do threads very well at all).

Answer 1

Just because you give a task to a thread pool executor doesn’t mean you can’t hold a reference on it. Keep a reference on the task, and if the user chooses to cancel it, then call abort on your task.

public class MyAbortableRunnable implements Runnable {
    private final Object lock = new Object();
    private AbortableHttpRequest request;

    public void abort() {
        synchronized(lock) {
            if (request != null) {
                request.abort();
            }
        }
    }

    @Override
    public void run() {
        ...
        // create the request
        synchronized(lock) {
            this.request = ...;
        }
        ...
    }
}