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/*
* 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.rxjava3.subscribers;
import java.util.concurrent.atomic.AtomicReference;
import org.reactivestreams.Subscription;
import io.reactivex.rxjava3.core.FlowableSubscriber;
import io.reactivex.rxjava3.disposables.Disposable;
import io.reactivex.rxjava3.internal.subscriptions.SubscriptionHelper;
import io.reactivex.rxjava3.internal.util.EndConsumerHelper;
/**
* An abstract Subscriber that allows asynchronous, external cancellation by implementing {@link Disposable}.
*
* All pre-implemented final methods are thread-safe.
*
*
The default {@link #onStart()} requests {@link Long#MAX_VALUE} by default. Override
* the method to request a custom positive amount. Use the protected {@link #request(long)}
* to request more items and {@link #cancel()} to cancel the sequence from within an
* {@code onNext} implementation.
*
*
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.
*
*
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) multiple times."}.
*
* 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.rxjava3.core.Flowable#safeSubscribe(org.reactivestreams.Subscriber)}
* instead of the standard {@code subscribe()} method.
*
*
Example
* 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();
*
* @param the received value type.
*/
public abstract class DisposableSubscriber implements FlowableSubscriber, Disposable {
final AtomicReference upstream = new AtomicReference<>();
@Override
public final void onSubscribe(Subscription s) {
if (EndConsumerHelper.setOnce(this.upstream, s, getClass())) {
onStart();
}
}
/**
* Called once the single upstream {@link Subscription} is set via {@link #onSubscribe(Subscription)}.
*/
protected void onStart() {
upstream.get().request(Long.MAX_VALUE);
}
/**
* Requests the specified amount from the upstream if its {@link Subscription} is set via
* onSubscribe already.
* Note that calling this method before a {@link Subscription} is set via {@link #onSubscribe(Subscription)}
* leads to {@link NullPointerException} and meant to be called from inside {@link #onStart()} or
* {@link #onNext(Object)}.
* @param n the request amount, positive
*/
protected final void request(long n) {
upstream.get().request(n);
}
/**
* Cancels the Subscription set via {@link #onSubscribe(Subscription)} or makes sure a
* {@link Subscription} set asynchronously (later) is cancelled immediately.
*
This method is thread-safe and can be exposed as a public API.
*/
protected final void cancel() {
dispose();
}
@Override
public final boolean isDisposed() {
return upstream.get() == SubscriptionHelper.CANCELLED;
}
@Override
public final void dispose() {
SubscriptionHelper.cancel(upstream);
}
}