/**
* 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.CheckReturnValue;
import java.util.concurrent.atomic.*;
import io.reactivex.Observer;
import io.reactivex.disposables.Disposable;
import io.reactivex.plugins.RxJavaPlugins;
/**
* Subject that, once an {@link Observer} has subscribed, emits all subsequently observed items to the
* subscriber.
* <p>
* <img width="640" height="405" src="https://raw.github.com/wiki/ReactiveX/RxJava/images/rx-operators/S.PublishSubject.png" alt="">
* <p>
* Example usage:
* <p>
* <pre> {@code
PublishSubject<Object> subject = PublishSubject.create();
// observer1 will receive all onNext and onComplete events
subject.subscribe(observer1);
subject.onNext("one");
subject.onNext("two");
// observer2 will only receive "three" and onComplete
subject.subscribe(observer2);
subject.onNext("three");
subject.onComplete();
} </pre>
*
* @param <T>
* the type of items observed and emitted by the Subject
*/
public final class PublishSubject<T> extends Subject<T> {
/** The terminated indicator for the subscribers array. */
@SuppressWarnings("rawtypes")
static final PublishDisposable[] TERMINATED = new PublishDisposable[0];
/** 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<PublishDisposable<T>[]> subscribers;
/** The error, write before terminating and read after checking subscribers. */
Throwable error;
/**
* Constructs a PublishSubject.
* @param <T> the value type
* @return the new PublishSubject
*/
@CheckReturnValue
public static <T> PublishSubject<T> create() {
return new PublishSubject<T>();
}
/**
* Constructs a PublishSubject.
* @since 2.0
*/
@SuppressWarnings("unchecked")
PublishSubject() {
subscribers = new AtomicReference<PublishDisposable<T>[]>(EMPTY);
}
@Override
public void subscribeActual(Observer<? super T> t) {
PublishDisposable<T> ps = new PublishDisposable<T>(t, this);
t.onSubscribe(ps);
if (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);
}
} else {
Throwable ex = error;
if (ex != null) {
t.onError(ex);
} else {
t.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(PublishDisposable<T> ps) {
for (;;) {
PublishDisposable<T>[] a = subscribers.get();
if (a == TERMINATED) {
return false;
}
int n = a.length;
@SuppressWarnings("unchecked")
PublishDisposable<T>[] b = new PublishDisposable[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(PublishDisposable<T> ps) {
for (;;) {
PublishDisposable<T>[] a = subscribers.get();
if (a == TERMINATED || 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<T>[] 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 onSubscribe(Disposable s) {
if (subscribers.get() == TERMINATED) {
s.dispose();
}
}
@Override
public void onNext(T t) {
if (subscribers.get() == TERMINATED) {
return;
}
if (t == null) {
onError(new NullPointerException("onNext called with null. Null values are generally not allowed in 2.x operators and sources."));
return;
}
for (PublishDisposable<T> s : subscribers.get()) {
s.onNext(t);
}
}
@SuppressWarnings("unchecked")
@Override
public void onError(Throwable t) {
if (subscribers.get() == TERMINATED) {
RxJavaPlugins.onError(t);
return;
}
if (t == null) {
t = new NullPointerException("onError called with null. Null values are generally not allowed in 2.x operators and sources.");
}
error = t;
for (PublishDisposable<T> s : subscribers.getAndSet(TERMINATED)) {
s.onError(t);
}
}
@SuppressWarnings("unchecked")
@Override
public void onComplete() {
if (subscribers.get() == TERMINATED) {
return;
}
for (PublishDisposable<T> s : subscribers.getAndSet(TERMINATED)) {
s.onComplete();
}
}
@Override
public boolean hasObservers() {
return subscribers.get().length != 0;
}
@Override
public Throwable getThrowable() {
if (subscribers.get() == TERMINATED) {
return error;
}
return null;
}
@Override
public boolean hasThrowable() {
return subscribers.get() == TERMINATED && error != null;
}
@Override
public boolean hasComplete() {
return subscribers.get() == TERMINATED && error == null;
}
/**
* Wraps the actual subscriber, tracks its requests and makes cancellation
* to remove itself from the current subscribers array.
*
* @param <T> the value type
*/
static final class PublishDisposable<T> extends AtomicBoolean implements Disposable {
private static final long serialVersionUID = 3562861878281475070L;
/** The actual subscriber. */
final Observer<? super T> actual;
/** The subject state. */
final PublishSubject<T> parent;
/**
* Constructs a PublishSubscriber, wraps the actual subscriber and the state.
* @param actual the actual subscriber
* @param parent the parent PublishProcessor
*/
PublishDisposable(Observer<? super T> actual, PublishSubject<T> parent) {
this.actual = actual;
this.parent = parent;
}
public void onNext(T t) {
if (!get()) {
actual.onNext(t);
}
}
public void onError(Throwable t) {
if (get()) {
RxJavaPlugins.onError(t);
} else {
actual.onError(t);
}
}
public void onComplete() {
if (!get()) {
actual.onComplete();
}
}
@Override
public void dispose() {
if (compareAndSet(false, true)) {
parent.remove(this);
}
}
@Override
public boolean isDisposed() {
return get();
}
}
}