/** * Copyright (c) 2016-present, RxJava Contributors. * * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in * compliance with the License. You may obtain a copy of the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software distributed under the License is * distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See * the License for the specific language governing permissions and limitations under the License. */ package io.reactivex.subscribers; import java.util.concurrent.atomic.AtomicReference; import org.reactivestreams.Subscription; import io.reactivex.FlowableSubscriber; import io.reactivex.disposables.Disposable; import io.reactivex.internal.subscriptions.SubscriptionHelper; import io.reactivex.internal.util.EndConsumerHelper; /** * An abstract Subscriber that allows asynchronous, external cancellation by implementing Disposable. * * <p>All pre-implemented final methods are thread-safe. * * <p>The default {@link #onStart()} requests Long.MAX_VALUE by default. Override * the method to request a custom <em>positive</em> amount. Use the protected {@link #request(long)} * to request more items and {@link #cancel()} to cancel the sequence from within an * {@code onNext} implementation. * * <p>Note that calling {@link #request(long)} from {@link #onStart()} may trigger * an immediate, asynchronous emission of data to {@link #onNext(Object)}. Make sure * all initialization happens before the call to {@code request()} in {@code onStart()}. * Calling {@link #request(long)} inside {@link #onNext(Object)} can happen at any time * because by design, {@code onNext} calls from upstream are non-reentrant and non-overlapping. * * <p>Like all other consumers, {@code DisposableSubscriber} can be subscribed only once. * Any subsequent attempt to subscribe it to a new source will yield an * {@link IllegalStateException} with message {@code "It is not allowed to subscribe with a(n) <class name> multiple times."}. * * <p>Implementation of {@link #onStart()}, {@link #onNext(Object)}, {@link #onError(Throwable)} * and {@link #onComplete()} are not allowed to throw any unchecked exceptions. * If for some reason this can't be avoided, use {@link io.reactivex.Flowable#safeSubscribe(org.reactivestreams.Subscriber)} * instead of the standard {@code subscribe()} method. * * <p>Example<pre><code> * Disposable d = * Flowable.range(1, 5) * .subscribeWith(new DisposableSubscriber<Integer>() { * @Override public void onStart() { * request(1); * } * @Override public void onNext(Integer t) { * if (t == 3) { * cancel(); * } * System.out.println(t); * request(1); * } * @Override public void onError(Throwable t) { * t.printStackTrace(); * } * @Override public void onComplete() { * System.out.println("Done!"); * } * }); * // ... * d.dispose(); * </code></pre> * @param <T> the received value type. */ public abstract class DisposableSubscriber<T> implements FlowableSubscriber<T>, Disposable { final AtomicReference<Subscription> s = new AtomicReference<Subscription>(); @Override public final void onSubscribe(Subscription s) { if (EndConsumerHelper.setOnce(this.s, s, getClass())) { onStart(); } } /** * Called once the single upstream Subscription is set via onSubscribe. */ protected void onStart() { s.get().request(Long.MAX_VALUE); } /** * Requests the specified amount from the upstream if its Subscription is set via * onSubscribe already. * <p>Note that calling this method before a Subscription is set via onSubscribe * leads to NullPointerException and meant to be called from inside onStart or * onNext. * @param n the request amount, positive */ protected final void request(long n) { s.get().request(n); } /** * Cancels the Subscription set via onSubscribe or makes sure a * Subscription set asynchronously (later) is cancelled immediately. * <p>This method is thread-safe and can be exposed as a public API. */ protected final void cancel() { dispose(); } @Override public final boolean isDisposed() { return s.get() == SubscriptionHelper.CANCELLED; } @Override public final void dispose() { SubscriptionHelper.cancel(s); } }