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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.observers;

import java.util.Objects;
import java.util.concurrent.atomic.AtomicReference;

import io.reactivex.rxjava3.annotations.NonNull;
import io.reactivex.rxjava3.core.MaybeObserver;
import io.reactivex.rxjava3.disposables.Disposable;
import io.reactivex.rxjava3.internal.disposables.*;
import io.reactivex.rxjava3.internal.util.EndConsumerHelper;

/**
 * An abstract {@link MaybeObserver} that allows asynchronous cancellation of its subscription and associated resources.
 *
 * 

All pre-implemented final methods are thread-safe. * *

Note that {@link #onSuccess(Object)}, {@link #onError(Throwable)} and {@link #onComplete()} are * exclusive to each other, unlike a regular {@link io.reactivex.rxjava3.core.Observer Observer}, and * {@code onComplete()} is never called after an {@code onSuccess()}. * *

Override the protected {@link #onStart()} to perform initialization when this * {@code ResourceMaybeObserver} is subscribed to a source. * *

Use the public {@link #dispose()} method to dispose the sequence externally and release * all resources. * *

To release the associated resources, one has to call {@link #dispose()} * in {@code onSuccess()}, {@code onError()} and {@code onComplete()} explicitly. * *

Use {@link #add(Disposable)} to associate resources (as {@link io.reactivex.rxjava3.disposables.Disposable Disposable}s) * with this {@code ResourceMaybeObserver} 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.rxjava3.disposables.CompositeDisposable CompositeDisposable}, associate it with this * {@code ResourceMaybeObserver} and then add/remove resources to/from the {@code CompositeDisposable} * freely. * *

Like all other consumers, {@code ResourceMaybeObserver} 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 #onSuccess(Object)}, {@link #onError(Throwable)} * and {@link #onComplete()} are not allowed to throw any unchecked exceptions. * *

Example


 * Disposable d =
 *     Maybe.just(1).delay(1, TimeUnit.SECONDS)
 *     .subscribeWith(new ResourceMaybeObserver<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();
 *         }
 *         @Override public void onComplete() {
 *             System.out.println("Done!");
 *             dispose();
 *         }
 *     });
 * // ...
 * d.dispose();
 * 
* * @param the value type */ public abstract class ResourceMaybeObserver implements MaybeObserver, Disposable { /** The active subscription. */ private final AtomicReference upstream = new AtomicReference<>(); /** The resource composite, can never be null. */ private final ListCompositeDisposable resources = new ListCompositeDisposable(); /** * Adds a resource to this {@code ResourceMaybeObserver}. * * @param resource the resource to add * * @throws NullPointerException if resource is {@code null} */ public final void add(@NonNull Disposable resource) { Objects.requireNonNull(resource, "resource is null"); resources.add(resource); } @Override public final void onSubscribe(@NonNull Disposable d) { if (EndConsumerHelper.setOnce(this.upstream, d, getClass())) { onStart(); } } /** * Called once the upstream sets a {@link Disposable} on this {@code ResourceMaybeObserver}. * *

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 {@code ResourceMaybeObserver} (if any). * *

This method can be called before the upstream calls {@link #onSubscribe(Disposable)} at which * case the main {@link Disposable} will be immediately disposed. */ @Override public final void dispose() { if (DisposableHelper.dispose(upstream)) { resources.dispose(); } } /** * Returns true if this {@code ResourceMaybeObserver} has been disposed/cancelled. * @return true if this {@code ResourceMaybeObserver} has been disposed/cancelled */ @Override public final boolean isDisposed() { return DisposableHelper.isDisposed(upstream.get()); } }





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