Java Executor partial shutdown

Question

Lets have one classic Executor in application. Many parts of application use this executor for some computations, each computation can be cancelled, for this I can call shutdown() or shutdownNow() on Executor.

But I want to shutdown only part of tasks in Executor. Sadly I can't have access to Future objects, they are private part of computation implementation (actually computation is backed by actor framework jetlang)

I want something like Executor wrapper, which I could pass to computation and which should be backed by real Executor. Something like this:

// main application executor
Executor applicationExecutor = Executors.newCachedThreadPool();

// starting computation
Executor computationExecutor = new ExecutorWrapper(applicationExecutor);
Computation computation = new Computation(computationExecutor);
computation.start();

// cancelling computation
computation.cancel();
// shutting down only computation tasks
computationExecutor.shutdown();

// applicationExecutor remains running and happy

Or any other idea?

Answer 1

For those, who wants good ends: there is final solution, partially based of Ivan Sopov's answer. Luckily jetlang uses for running its tasks only Executor interface (not ExecutorService), so I make wrapper class which supports stopping tasks created only by this wrapper.

static class StoppableExecutor implements Executor {
    final ExecutorService executor;
    final List<Future<?>> futures = Lists.newArrayList();
    boolean stopped;

    public StoppableExecutor(ExecutorService executor) {
        this.executor = executor;
    }

    void stop() {
        this.stopped = true;
        synchronized (futures) {
            for (Iterator<Future<?>> iterator = futures.iterator(); iterator.hasNext();) {
                Future<?> future = iterator.next();
                if (!future.isDone() && !future.isCancelled()) {
                    System.out.println(future.cancel(true));
                }
            }
            futures.clear();
        }
    }

    @Override
    public void execute(Runnable command) {
        if (!stopped) {
            synchronized (futures) {
                Future<?> newFuture = executor.submit(command);
                for (Iterator<Future<?>> iterator = futures.iterator(); iterator.hasNext();) {
                    Future<?> future = iterator.next();
                    if (future.isDone() || future.isCancelled())
                        iterator.remove();
                }
                futures.add(newFuture);
            }
        }
    }
}

Using this is pretty straightforward:

ExecutorService service = Executors.newFixedThreadPool(5);
StoppableExecutor executor = new StoppableExecutor(service);

// doing some actor stuff with executor instance
PoolFiberFactory factory = new PoolFiberFactory(executor);

// stopping tasks only created on executor instance
// executor service is happily running other tasks
executor.stop();

That's all. Works nice.