/**
* 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.*;
import org.reactivestreams.Subscription;
import io.reactivex.FlowableSubscriber;
import io.reactivex.disposables.Disposable;
import io.reactivex.internal.disposables.ListCompositeDisposable;
import io.reactivex.internal.functions.ObjectHelper;
import io.reactivex.internal.subscriptions.SubscriptionHelper;
import io.reactivex.internal.util.EndConsumerHelper;
/**
* An abstract Subscriber that allows asynchronous cancellation of its
* subscription and associated resources.
*
* <p>All pre-implemented final methods are thread-safe.
*
* <p>To release the associated resources, one has to call {@link #dispose()}
* in {@code onError()} and {@code onComplete()} explicitly.
*
* <p>Use {@link #add(Disposable)} to associate resources (as {@link io.reactivex.disposables.Disposable Disposable}s)
* with this {@code ResourceSubscriber} that will be cleaned up when {@link #dispose()} is called.
* Removing previously associated resources is not possible but one can create a
* {@link io.reactivex.disposables.CompositeDisposable CompositeDisposable}, associate it with this
* {@code ResourceSubscriber} and then add/remove resources to/from the {@code CompositeDisposable}
* freely.
*
* <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 #dispose()} 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 ResourceSubscriber} 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 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();
* </code></pre>
*
* @param <T> the value type
*/
public abstract class ResourceSubscriber<T> implements FlowableSubscriber<T>, Disposable {
/** The active subscription. */
private final AtomicReference<Subscription> s = new AtomicReference<Subscription>();
/** The resource composite, can never be null. */
private final ListCompositeDisposable resources = new ListCompositeDisposable();
/** Remembers the request(n) counts until a subscription arrives. */
private final AtomicLong missedRequested = new AtomicLong();
/**
* Adds a resource to this AsyncObserver.
*
* @param resource the resource to add
*
* @throws NullPointerException if resource is null
*/
public final void add(Disposable resource) {
ObjectHelper.requireNonNull(resource, "resource is null");
resources.add(resource);
}
@Override
public final void onSubscribe(Subscription s) {
if (EndConsumerHelper.setOnce(this.s, s, getClass())) {
long r = missedRequested.getAndSet(0L);
if (r != 0L) {
s.request(r);
}
onStart();
}
}
/**
* Called once the upstream sets a Subscription on this AsyncObserver.
*
* <p>You can perform initialization at this moment. The default
* implementation requests Long.MAX_VALUE from upstream.
*/
protected void onStart() {
request(Long.MAX_VALUE);
}
/**
* Request the specified amount of elements from upstream.
*
* <p>This method can be called before the upstream calls onSubscribe().
* When the subscription happens, all missed requests are requested.
*
* @param n the request amount, must be positive
*/
protected final void request(long n) {
SubscriptionHelper.deferredRequest(s, missedRequested, n);
}
/**
* Cancels the subscription (if any) and disposes the resources associated with
* this AsyncObserver (if any).
*
* <p>This method can be called before the upstream calls onSubscribe at which
* case the Subscription will be immediately cancelled.
*/
@Override
public final void dispose() {
if (SubscriptionHelper.cancel(s)) {
resources.dispose();
}
}
/**
* Returns true if this AsyncObserver has been disposed/cancelled.
* @return true if this AsyncObserver has been disposed/cancelled
*/
@Override
public final boolean isDisposed() {
return SubscriptionHelper.isCancelled(s.get());
}
}