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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.subjects;

import java.util.concurrent.atomic.*;

import io.reactivex.*;
import io.reactivex.annotations.*;
import io.reactivex.disposables.Disposable;
import io.reactivex.internal.functions.ObjectHelper;
import io.reactivex.plugins.RxJavaPlugins;

/**
 * Represents a hot Maybe-like source and consumer of events similar to Subjects.
 * 

* *

* This subject does not have a public constructor by design; a new non-terminated instance of this * {@code MaybeSubject} can be created via the {@link #create()} method. *

* Since the {@code MaybeSubject} is conceptionally derived from the {@code Processor} type in the Reactive Streams specification, * {@code null}s are not allowed (Rule 2.13) * as parameters to {@link #onSuccess(Object)} and {@link #onError(Throwable)}. Such calls will result in a * {@link NullPointerException} being thrown and the subject's state is not changed. *

* Since a {@code MaybeSubject} is a {@link io.reactivex.Maybe}, calling {@code onSuccess}, {@code onError} * or {@code onComplete} will move this {@code MaybeSubject} into its terminal state atomically. *

* All methods are thread safe. Calling {@link #onSuccess(Object)} or {@link #onComplete()} multiple * times has no effect. Calling {@link #onError(Throwable)} multiple times relays the {@code Throwable} to * the {@link io.reactivex.plugins.RxJavaPlugins#onError(Throwable)} global error handler. *

* Even though {@code MaybeSubject} implements the {@code MaybeObserver} interface, calling * {@code onSubscribe} is not required (Rule 2.12) * if the subject is used as a standalone source. However, calling {@code onSubscribe} * after the {@code MaybeSubject} reached its terminal state will result in the * given {@code Disposable} being disposed immediately. *

* This {@code MaybeSubject} supports the standard state-peeking methods {@link #hasComplete()}, {@link #hasThrowable()}, * {@link #getThrowable()} and {@link #hasObservers()} as well as means to read any success item in a non-blocking * and thread-safe manner via {@link #hasValue()} and {@link #getValue()}. *

* The {@code MaybeSubject} does not support clearing its cached {@code onSuccess} value. *

*
Scheduler:
*
{@code MaybeSubject} does not operate by default on a particular {@link io.reactivex.Scheduler} and * the {@code MaybeObserver}s get notified on the thread where the terminating {@code onSuccess}, {@code onError} or {@code onComplete} * methods were invoked.
*
Error handling:
*
When the {@link #onError(Throwable)} is called, the {@code MaybeSubject} enters into a terminal state * and emits the same {@code Throwable} instance to the last set of {@code MaybeObserver}s. During this emission, * if one or more {@code MaybeObserver}s dispose their respective {@code Disposable}s, the * {@code Throwable} is delivered to the global error handler via * {@link io.reactivex.plugins.RxJavaPlugins#onError(Throwable)} (multiple times if multiple {@code MaybeObserver}s * cancel at once). * If there were no {@code MaybeObserver}s subscribed to this {@code MaybeSubject} when the {@code onError()} * was called, the global error handler is not invoked. *
*
*

* Example usage: *


 * MaybeSubject<Integer> subject1 = MaybeSubject.create();
 *
 * TestObserver<Integer> to1 = subject1.test();
 *
 * // MaybeSubjects are empty by default
 * to1.assertEmpty();
 *
 * subject1.onSuccess(1);
 *
 * // onSuccess is a terminal event with MaybeSubjects
 * // TestObserver converts onSuccess into onNext + onComplete
 * to1.assertResult(1);
 *
 * TestObserver<Integer> to2 = subject1.test();
 *
 * // late Observers receive the terminal signal (onSuccess) too
 * to2.assertResult(1);
 *
 * // -----------------------------------------------------
 *
 * MaybeSubject<Integer> subject2 = MaybeSubject.create();
 *
 * TestObserver<Integer> to3 = subject2.test();
 *
 * subject2.onComplete();
 *
 * // a completed MaybeSubject completes its MaybeObservers
 * to3.assertResult();
 *
 * TestObserver<Integer> to4 = subject1.test();
 *
 * // late Observers receive the terminal signal (onComplete) too
 * to4.assertResult();
 * 
*

History: 2.0.5 - experimental * @param the value type received and emitted * @since 2.1 */ public final class MaybeSubject extends Maybe implements MaybeObserver { final AtomicReference[]> observers; @SuppressWarnings("rawtypes") static final MaybeDisposable[] EMPTY = new MaybeDisposable[0]; @SuppressWarnings("rawtypes") static final MaybeDisposable[] TERMINATED = new MaybeDisposable[0]; final AtomicBoolean once; T value; Throwable error; /** * Creates a fresh MaybeSubject. * @param the value type received and emitted * @return the new MaybeSubject instance */ @CheckReturnValue @NonNull public static MaybeSubject create() { return new MaybeSubject(); } @SuppressWarnings("unchecked") MaybeSubject() { once = new AtomicBoolean(); observers = new AtomicReference[]>(EMPTY); } @Override public void onSubscribe(Disposable d) { if (observers.get() == TERMINATED) { d.dispose(); } } @SuppressWarnings("unchecked") @Override public void onSuccess(T value) { ObjectHelper.requireNonNull(value, "onSuccess called with null. Null values are generally not allowed in 2.x operators and sources."); if (once.compareAndSet(false, true)) { this.value = value; for (MaybeDisposable md : observers.getAndSet(TERMINATED)) { md.downstream.onSuccess(value); } } } @SuppressWarnings("unchecked") @Override public void onError(Throwable e) { ObjectHelper.requireNonNull(e, "onError called with null. Null values are generally not allowed in 2.x operators and sources."); if (once.compareAndSet(false, true)) { this.error = e; for (MaybeDisposable md : observers.getAndSet(TERMINATED)) { md.downstream.onError(e); } } else { RxJavaPlugins.onError(e); } } @SuppressWarnings("unchecked") @Override public void onComplete() { if (once.compareAndSet(false, true)) { for (MaybeDisposable md : observers.getAndSet(TERMINATED)) { md.downstream.onComplete(); } } } @Override protected void subscribeActual(MaybeObserver observer) { MaybeDisposable md = new MaybeDisposable(observer, this); observer.onSubscribe(md); if (add(md)) { if (md.isDisposed()) { remove(md); } } else { Throwable ex = error; if (ex != null) { observer.onError(ex); } else { T v = value; if (v == null) { observer.onComplete(); } else { observer.onSuccess(v); } } } } boolean add(MaybeDisposable inner) { for (;;) { MaybeDisposable[] a = observers.get(); if (a == TERMINATED) { return false; } int n = a.length; @SuppressWarnings("unchecked") MaybeDisposable[] b = new MaybeDisposable[n + 1]; System.arraycopy(a, 0, b, 0, n); b[n] = inner; if (observers.compareAndSet(a, b)) { return true; } } } @SuppressWarnings("unchecked") void remove(MaybeDisposable inner) { for (;;) { MaybeDisposable[] a = observers.get(); int n = a.length; if (n == 0) { return; } int j = -1; for (int i = 0; i < n; i++) { if (a[i] == inner) { j = i; break; } } if (j < 0) { return; } MaybeDisposable[] b; if (n == 1) { b = EMPTY; } else { b = new MaybeDisposable[n - 1]; System.arraycopy(a, 0, b, 0, j); System.arraycopy(a, j + 1, b, j, n - j - 1); } if (observers.compareAndSet(a, b)) { return; } } } /** * Returns the success value if this MaybeSubject was terminated with a success value. * @return the success value or null */ @Nullable public T getValue() { if (observers.get() == TERMINATED) { return value; } return null; } /** * Returns true if this MaybeSubject was terminated with a success value. * @return true if this MaybeSubject was terminated with a success value */ public boolean hasValue() { return observers.get() == TERMINATED && value != null; } /** * Returns the terminal error if this MaybeSubject has been terminated with an error, null otherwise. * @return the terminal error or null if not terminated or not with an error */ @Nullable public Throwable getThrowable() { if (observers.get() == TERMINATED) { return error; } return null; } /** * Returns true if this MaybeSubject has been terminated with an error. * @return true if this MaybeSubject has been terminated with an error */ public boolean hasThrowable() { return observers.get() == TERMINATED && error != null; } /** * Returns true if this MaybeSubject has been completed. * @return true if this MaybeSubject has been completed */ public boolean hasComplete() { return observers.get() == TERMINATED && value == null && error == null; } /** * Returns true if this MaybeSubject has observers. * @return true if this MaybeSubject has observers */ public boolean hasObservers() { return observers.get().length != 0; } /** * Returns the number of current observers. * @return the number of current observers */ /* test */ int observerCount() { return observers.get().length; } static final class MaybeDisposable extends AtomicReference> implements Disposable { private static final long serialVersionUID = -7650903191002190468L; final MaybeObserver downstream; MaybeDisposable(MaybeObserver actual, MaybeSubject parent) { this.downstream = actual; lazySet(parent); } @Override public void dispose() { MaybeSubject parent = getAndSet(null); if (parent != null) { parent.remove(this); } } @Override public boolean isDisposed() { return get() == null; } } }





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