String msg = randomString();
Callable<String> callable = new AppendCallable(msg);
final CountDownLatch responseLatch = new CountDownLatch(1);
final AtomicReference<String> result = new AtomicReference<String>();
service.submitToKeyOwner(callable, "key", new ExecutionCallback<String>() {
public void onResponse(String response) {
result.set(response);
responseLatch.countDown();
}