An abstract Subscriber that allows asynchronous cancellation of its subscription and associated resources.

All pre-implemented final methods are thread-safe.

To release the associated resources, one has to call dispose() in onError() and onComplete() explicitly.

Use add(Disposable) to associate resources (as Disposables) with this ResourceSubscriber that will be cleaned up when dispose() is called. Removing previously associated resources is not possible but one can create a CompositeDisposable, associate it with this ResourceSubscriber and then add/remove resources to/from the CompositeDisposable freely.

The default onStart() requests Long#MAX_VALUE by default. Override the method to request a custom positive amount. Use the protected request(long) to request more items and dispose() to cancel the sequence from within an onNext implementation.

Note that calling request(long) from onStart() may trigger an immediate, asynchronous emission of data to onNext(Object). Make sure all initialization happens before the call to request() in onStart(). Calling request(long) inside onNext(Object) can happen at any time because by design, onNext calls from upstream are non-reentrant and non-overlapping.

Like all other consumers, ResourceSubscriber can be subscribed only once. Any subsequent attempt to subscribe it to a new source will yield an IllegalStateException with message "It is not allowed to subscribe with a(n) <class name> multiple times.".

Implementation of onStart(), onNext(Object), onError(Throwable) and onComplete() are not allowed to throw any unchecked exceptions. If for some reason this can't be avoided, use io.reactivex.rxjava3.core.Flowable#safeSubscribe(org.reactivestreams.Subscriber) instead of the standard subscribe() method.

Example

Disposable d =
    Flowable.range(1, 5)
    .subscribeWith(new ResourceSubscriber<Integer>() {
        @Override public void onStart() {
            add(Schedulers.single()
                .scheduleDirect(() -> System.out.println("Time!"),
                    2, TimeUnit.SECONDS));
            request(1);
        }
        @Override public void onNext(Integer t) {
            if (t == 3) {
                dispose();
            }
            System.out.println(t);
            request(1);
        }
        @Override public void onError(Throwable t) {
            t.printStackTrace();
            dispose();
        }
        @Override public void onComplete() {
            System.out.println("Done!");
            dispose();
        }
    });
// ...
d.dispose();