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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 io.reactivex.annotations.Nullable;
import io.reactivex.annotations.NonNull;
import java.util.Arrays;
import java.util.concurrent.atomic.AtomicReference;

import io.reactivex.Observer;
import io.reactivex.annotations.CheckReturnValue;
import io.reactivex.disposables.Disposable;
import io.reactivex.internal.functions.ObjectHelper;
import io.reactivex.internal.observers.DeferredScalarDisposable;
import io.reactivex.plugins.RxJavaPlugins;

/**
 * A Subject that emits the very last value followed by a completion event or the received error to Observers.
 * 

* *

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

* Since a {@code Subject} 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 #onNext(Object)} and {@link #onError(Throwable)}. Such calls will result in a * {@link NullPointerException} being thrown and the subject's state is not changed. *

* Since an {@code AsyncSubject} is an {@link io.reactivex.Observable}, it does not support backpressure. *

* When this {@code AsyncSubject} is terminated via {@link #onError(Throwable)}, the * last observed item (if any) is cleared and late {@link io.reactivex.Observer}s only receive * the {@code onError} event. *

* The {@code AsyncSubject} caches the latest item internally and it emits this item only when {@code onComplete} is called. * Therefore, it is not recommended to use this {@code Subject} with infinite or never-completing sources. *

* Even though {@code AsyncSubject} implements the {@code Observer} 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 AsyncSubject} reached its terminal state will result in the * given {@code Disposable} being disposed immediately. *

* Calling {@link #onNext(Object)}, {@link #onError(Throwable)} and {@link #onComplete()} * is required to be serialized (called from the same thread or called non-overlappingly from different threads * through external means of serialization). The {@link #toSerialized()} method available to all {@code Subject}s * provides such serialization and also protects against reentrance (i.e., when a downstream {@code Observer} * consuming this subject also wants to call {@link #onNext(Object)} on this subject recursively). * The implementation of onXXX methods are technically thread-safe but non-serialized calls * to them may lead to undefined state in the currently subscribed Observers. *

* This {@code AsyncSubject} supports the standard state-peeking methods {@link #hasComplete()}, {@link #hasThrowable()}, * {@link #getThrowable()} and {@link #hasObservers()} as well as means to read the very last observed value - * after this {@code AsyncSubject} has been completed - in a non-blocking and thread-safe * manner via {@link #hasValue()}, {@link #getValue()}, {@link #getValues()} or {@link #getValues(Object[])}. *

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

* Example usage: *


 * AsyncSubject<Object> subject = AsyncSubject.create();
 * 
 * TestObserver<Object> to1 = subject.test();
 *
 * to1.assertEmpty();
 *
 * subject.onNext(1);
 *
 * // AsyncSubject only emits when onComplete was called.
 * to1.assertEmpty();
 *
 * subject.onNext(2);
 * subject.onComplete();
 *
 * // onComplete triggers the emission of the last cached item and the onComplete event.
 * to1.assertResult(2);
 *
 * TestObserver<Object> to2 = subject.test();
 *
 * // late Observers receive the last cached item too
 * to2.assertResult(2);
 * 
* @param the value type */ public final class AsyncSubject extends Subject { @SuppressWarnings("rawtypes") static final AsyncDisposable[] EMPTY = new AsyncDisposable[0]; @SuppressWarnings("rawtypes") static final AsyncDisposable[] TERMINATED = new AsyncDisposable[0]; final AtomicReference[]> subscribers; /** Write before updating subscribers, read after reading subscribers as TERMINATED. */ Throwable error; /** Write before updating subscribers, read after reading subscribers as TERMINATED. */ T value; /** * Creates a new AsyncProcessor. * @param the value type to be received and emitted * @return the new AsyncProcessor instance */ @CheckReturnValue @NonNull public static AsyncSubject create() { return new AsyncSubject(); } /** * Constructs an AsyncSubject. * @since 2.0 */ @SuppressWarnings("unchecked") AsyncSubject() { this.subscribers = new AtomicReference[]>(EMPTY); } @Override public void onSubscribe(Disposable d) { if (subscribers.get() == TERMINATED) { d.dispose(); } } @Override public void onNext(T t) { ObjectHelper.requireNonNull(t, "onNext called with null. Null values are generally not allowed in 2.x operators and sources."); if (subscribers.get() == TERMINATED) { return; } value = t; } @SuppressWarnings("unchecked") @Override public void onError(Throwable t) { ObjectHelper.requireNonNull(t, "onError called with null. Null values are generally not allowed in 2.x operators and sources."); if (subscribers.get() == TERMINATED) { RxJavaPlugins.onError(t); return; } value = null; error = t; for (AsyncDisposable as : subscribers.getAndSet(TERMINATED)) { as.onError(t); } } @SuppressWarnings("unchecked") @Override public void onComplete() { if (subscribers.get() == TERMINATED) { return; } T v = value; AsyncDisposable[] array = subscribers.getAndSet(TERMINATED); if (v == null) { for (AsyncDisposable as : array) { as.onComplete(); } } else { for (AsyncDisposable as : array) { as.complete(v); } } } @Override public boolean hasObservers() { return subscribers.get().length != 0; } @Override public boolean hasThrowable() { return subscribers.get() == TERMINATED && error != null; } @Override public boolean hasComplete() { return subscribers.get() == TERMINATED && error == null; } @Override public Throwable getThrowable() { return subscribers.get() == TERMINATED ? error : null; } @Override protected void subscribeActual(Observer observer) { AsyncDisposable as = new AsyncDisposable(observer, this); observer.onSubscribe(as); if (add(as)) { if (as.isDisposed()) { remove(as); } } else { Throwable ex = error; if (ex != null) { observer.onError(ex); } else { T v = value; if (v != null) { as.complete(v); } else { as.onComplete(); } } } } /** * Tries to add the given subscriber to the subscribers array atomically * or returns false if the subject has terminated. * @param ps the subscriber to add * @return true if successful, false if the subject has terminated */ boolean add(AsyncDisposable ps) { for (;;) { AsyncDisposable[] a = subscribers.get(); if (a == TERMINATED) { return false; } int n = a.length; @SuppressWarnings("unchecked") AsyncDisposable[] b = new AsyncDisposable[n + 1]; System.arraycopy(a, 0, b, 0, n); b[n] = ps; if (subscribers.compareAndSet(a, b)) { return true; } } } /** * Atomically removes the given subscriber if it is subscribed to the subject. * @param ps the subject to remove */ @SuppressWarnings("unchecked") void remove(AsyncDisposable ps) { for (;;) { AsyncDisposable[] a = subscribers.get(); int n = a.length; if (n == 0) { return; } int j = -1; for (int i = 0; i < n; i++) { if (a[i] == ps) { j = i; break; } } if (j < 0) { return; } AsyncDisposable[] b; if (n == 1) { b = EMPTY; } else { b = new AsyncDisposable[n - 1]; System.arraycopy(a, 0, b, 0, j); System.arraycopy(a, j + 1, b, j, n - j - 1); } if (subscribers.compareAndSet(a, b)) { return; } } } /** * Returns true if the subject has any value. *

The method is thread-safe. * @return true if the subject has any value */ public boolean hasValue() { return subscribers.get() == TERMINATED && value != null; } /** * Returns a single value the Subject currently has or null if no such value exists. *

The method is thread-safe. * @return a single value the Subject currently has or null if no such value exists */ @Nullable public T getValue() { return subscribers.get() == TERMINATED ? value : null; } /** * Returns an Object array containing snapshot all values of the Subject. *

The method is thread-safe. * @return the array containing the snapshot of all values of the Subject * @deprecated in 2.1.14; put the result of {@link #getValue()} into an array manually, will be removed in 3.x */ @Deprecated public Object[] getValues() { T v = getValue(); return v != null ? new Object[] { v } : new Object[0]; } /** * Returns a typed array containing a snapshot of all values of the Subject. *

The method follows the conventions of Collection.toArray by setting the array element * after the last value to null (if the capacity permits). *

The method is thread-safe. * @param array the target array to copy values into if it fits * @return the given array if the values fit into it or a new array containing all values * @deprecated in 2.1.14; put the result of {@link #getValue()} into an array manually, will be removed in 3.x */ @Deprecated public T[] getValues(T[] array) { T v = getValue(); if (v == null) { if (array.length != 0) { array[0] = null; } return array; } if (array.length == 0) { array = Arrays.copyOf(array, 1); } array[0] = v; if (array.length != 1) { array[1] = null; } return array; } static final class AsyncDisposable extends DeferredScalarDisposable { private static final long serialVersionUID = 5629876084736248016L; final AsyncSubject parent; AsyncDisposable(Observer actual, AsyncSubject parent) { super(actual); this.parent = parent; } @Override public void dispose() { if (super.tryDispose()) { parent.remove(this); } } void onComplete() { if (!isDisposed()) { downstream.onComplete(); } } void onError(Throwable t) { if (isDisposed()) { RxJavaPlugins.onError(t); } else { downstream.onError(t); } } } }





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