/**
* 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.observers;
import java.util.concurrent.atomic.AtomicReference;
import io.reactivex.SingleObserver;
import io.reactivex.annotations.NonNull;
import io.reactivex.disposables.Disposable;
import io.reactivex.internal.disposables.*;
import io.reactivex.internal.functions.ObjectHelper;
import io.reactivex.internal.util.EndConsumerHelper;
/**
* An abstract {@link SingleObserver} that allows asynchronous cancellation of its subscription
* and the associated resources.
*
* <p>All pre-implemented final methods are thread-safe.
*
* <p>Override the protected {@link #onStart()} to perform initialization when this
* {@code ResourceSingleObserver} is subscribed to a source.
*
* <p>Use the public {@link #dispose()} method to dispose the sequence externally and release
* all resources.
*
* <p>To release the associated resources, one has to call {@link #dispose()}
* in {@code onSuccess()} and {@code onError()} explicitly.
*
* <p>Use {@link #add(Disposable)} to associate resources (as {@link io.reactivex.disposables.Disposable Disposable}s)
* with this {@code ResourceSingleObserver} 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 ResourceSingleObserver} and then add/remove resources to/from the {@code CompositeDisposable}
* freely.
*
* <p>Like all other consumers, {@code ResourceSingleObserver} 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 #onSuccess(Object)} and {@link #onError(Throwable)}
* are not allowed to throw any unchecked exceptions.
*
* <p>Example<pre><code>
* Disposable d =
* Single.just(1).delay(1, TimeUnit.SECONDS)
* .subscribeWith(new ResourceSingleObserver<Integer>() {
* @Override public void onStart() {
* add(Schedulers.single()
* .scheduleDirect(() -> System.out.println("Time!"),
* 2, TimeUnit.SECONDS));
* }
* @Override public void onSuccess(Integer t) {
* System.out.println(t);
* dispose();
* }
* @Override public void onError(Throwable t) {
* t.printStackTrace();
* dispose();
* }
* });
* // ...
* d.dispose();
* </code></pre>
*
* @param <T> the value type
*/
public abstract class ResourceSingleObserver<T> implements SingleObserver<T>, Disposable {
/** The active subscription. */
private final AtomicReference<Disposable> s = new AtomicReference<Disposable>();
/** The resource composite, can never be null. */
private final ListCompositeDisposable resources = new ListCompositeDisposable();
/**
* Adds a resource to this ResourceObserver.
*
* @param resource the resource to add
*
* @throws NullPointerException if resource is null
*/
public final void add(@NonNull Disposable resource) {
ObjectHelper.requireNonNull(resource, "resource is null");
resources.add(resource);
}
@Override
public final void onSubscribe(@NonNull Disposable s) {
if (EndConsumerHelper.setOnce(this.s, s, getClass())) {
onStart();
}
}
/**
* Called once the upstream sets a Subscription on this ResourceObserver.
*
* <p>You can perform initialization at this moment. The default
* implementation does nothing.
*/
protected void onStart() {
}
/**
* Cancels the main disposable (if any) and disposes the resources associated with
* this ResourceObserver (if any).
*
* <p>This method can be called before the upstream calls onSubscribe at which
* case the main Disposable will be immediately disposed.
*/
@Override
public final void dispose() {
if (DisposableHelper.dispose(s)) {
resources.dispose();
}
}
/**
* Returns true if this ResourceObserver has been disposed/cancelled.
* @return true if this ResourceObserver has been disposed/cancelled
*/
@Override
public final boolean isDisposed() {
return DisposableHelper.isDisposed(s.get());
}
}