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Objects that are both an Observable and a Consumer.
/**
* 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 com.jakewharton.rxrelay2;
import io.reactivex.Observer;
import io.reactivex.annotations.CheckReturnValue;
import io.reactivex.annotations.NonNull;
import io.reactivex.disposables.Disposable;
import io.reactivex.subjects.PublishSubject;
import java.util.concurrent.atomic.AtomicBoolean;
import java.util.concurrent.atomic.AtomicReference;
/**
* Relay that, once an {@link Observer} has subscribed, emits all subsequently observed items to the
* subscriber.
*
* 
*
* Example usage:
*
*
{@code
PublishRelay
*/
public final class PublishRelay extends Relay {
/** An empty subscribers array to avoid allocating it all the time. */
@SuppressWarnings("rawtypes")
static final PublishDisposable[] EMPTY = new PublishDisposable[0];
/** The array of currently subscribed subscribers. */
final AtomicReference[]> subscribers;
/**
* Constructs a PublishRelay.
*/
@CheckReturnValue
@NonNull
public static PublishRelay create() {
return new PublishRelay();
}
/**
* Constructs a PublishRelay.
*/
@SuppressWarnings("unchecked")
PublishRelay() {
subscribers = new AtomicReference[]>(EMPTY);
}
@Override
protected void subscribeActual(Observer t) {
PublishDisposable ps = new PublishDisposable(t, this);
t.onSubscribe(ps);
add(ps);
// if cancellation happened while a successful add, the remove() didn't work
// so we need to do it again
if (ps.isDisposed()) {
remove(ps);
}
}
/**
* Adds the given subscriber to the subscribers array atomically.
* @param ps the subscriber to add
*/
void add(PublishDisposable ps) {
for (;;) {
PublishDisposable[] a = subscribers.get();
int n = a.length;
@SuppressWarnings("unchecked")
PublishDisposable[] b = new PublishDisposable[n + 1];
System.arraycopy(a, 0, b, 0, n);
b[n] = ps;
if (subscribers.compareAndSet(a, b)) {
return;
}
}
}
/**
* Atomically removes the given subscriber if it is subscribed to the subject.
* @param ps the subject to remove
*/
@SuppressWarnings("unchecked")
void remove(PublishDisposable ps) {
for (;;) {
PublishDisposable[] a = subscribers.get();
if (a == EMPTY) {
return;
}
int n = a.length;
int j = -1;
for (int i = 0; i < n; i++) {
if (a[i] == ps) {
j = i;
break;
}
}
if (j < 0) {
return;
}
PublishDisposable[] b;
if (n == 1) {
b = EMPTY;
} else {
b = new PublishDisposable[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;
}
}
}
@Override
public void accept(T value) {
if (value == null) throw new NullPointerException("value == null");
for (PublishDisposable s : subscribers.get()) {
s.onNext(value);
}
}
@Override
public boolean hasObservers() {
return subscribers.get().length != 0;
}
/**
* Wraps the actual subscriber, tracks its requests and makes cancellation
* to remove itself from the current subscribers array.
*
* @param the value type
*/
static final class PublishDisposable extends AtomicBoolean implements Disposable {
private static final long serialVersionUID = 3562861878281475070L;
/** The actual subscriber. */
final Observer downstream;
/** The subject state. */
final PublishRelay parent;
/**
* Constructs a PublishSubscriber, wraps the actual subscriber and the state.
* @param actual the actual subscriber
* @param parent the parent PublishProcessor
*/
PublishDisposable(Observer actual, PublishRelay parent) {
this.downstream = actual;
this.parent = parent;
}
public void onNext(T t) {
if (!get()) {
downstream.onNext(t);
}
}
@Override
public void dispose() {
if (compareAndSet(false, true)) {
parent.remove(this);
}
}
@Override
public boolean isDisposed() {
return get();
}
}
}