FutureManager.java

import java.util.HashMap;
import java.util.Map;
import java.util.concurrent.Executor;
import java.util.concurrent.Executors;
import java.util.concurrent.Future;

public class FutureManager {
    Executor executor = Executors.newSingleThreadExecutor();
    Map<String, Future> futures;
    long timeToSleep;

    public FutureManager(long sleep) {
        this.timeToSleep = sleep;
        futures = new HashMap<>();

        Thread t = new Thread(new Runnable() {
            @Override
            public void run() {
                try {
                    for (Map.Entry<String, Future> e : futures.entrySet()) {
                        if (e.getValue().isDone()) {
                            cleanup(e.getKey()); // cleanup
                        }
                    }

                    Thread.sleep(timeToSleep);
                } catch (InterruptedException e) {
                    // ignore it and exit.
                }
            }
        });

        executor.execute(t);
    }

    private void cleanup(String id) {
        this.futures.remove(id);
    }

    public void add(String id, Future f) {
        futures.put(id, f);
    }

    public void cancel(String id) {
        Future f = futures.get(id);
        if (f != null) {
            f.cancel(true);
        }
        cleanup(id);
    }
}