Calling unsubscribe() and isUnsubscribed() is thread-safe and can happen at any time, even before or during an active rx.Completable#subscribe(CompletableSubscriber) call.

Override the onStart() method to execute custom logic on the very first successful onSubscribe call.

If one wants to remain consistent regarding isUnsubscribed() and being terminated, the clear() method should be called from the implementing onError and onCompleted methods.

public final class MyCompletableSubscriber extends AsyncCompletableSubscriber {
    @Override
    public void onStart() {
        System.out.println("Started!");
    }

    @Override
    public void onCompleted() {
        System.out.println("Completed!");
        clear();
    }

    @Override
    public void onError(Throwable e) {
        e.printStackTrace();
        clear();
    }
}