/**
* 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.processors;
import java.util.concurrent.atomic.*;
import org.reactivestreams.*;
import io.reactivex.annotations.*;
import io.reactivex.exceptions.MissingBackpressureException;
import io.reactivex.internal.subscriptions.SubscriptionHelper;
import io.reactivex.internal.util.BackpressureHelper;
import io.reactivex.plugins.RxJavaPlugins;
/**
* Processor that multicasts all subsequently observed items to its current {@link Subscriber}s.
*
* <p>
* <img width="640" height="405" src="https://raw.github.com/wiki/ReactiveX/RxJava/images/rx-operators/S.PublishSubject.png" alt="">
*
* <p>The processor does not coordinate backpressure for its subscribers and implements a weaker onSubscribe which
* calls requests Long.MAX_VALUE from the incoming Subscriptions. This makes it possible to subscribe the PublishProcessor
* to multiple sources (note on serialization though) unlike the standard Subscriber contract. Child subscribers, however, are not overflown but receive an
* IllegalStateException in case their requested amount is zero.
*
* <p>The implementation of onXXX methods are technically thread-safe but non-serialized calls
* to them may lead to undefined state in the currently subscribed Subscribers.
*
* <p>Due to the nature Flowables are constructed, the PublishProcessor can't be instantiated through
* {@code new} but must be created via the {@link #create()} method.
*
* Example usage:
* <p>
* <pre> {@code
PublishProcessor<Object> processor = PublishProcessor.create();
// subscriber1 will receive all onNext and onComplete events
processor.subscribe(subscriber1);
processor.onNext("one");
processor.onNext("two");
// subscriber2 will only receive "three" and onComplete
processor.subscribe(subscriber2);
processor.onNext("three");
processor.onComplete();
} </pre>
* @param <T> the value type multicasted to Subscribers.
*/
public final class PublishProcessor<T> extends FlowableProcessor<T> {
/** The terminated indicator for the subscribers array. */
@SuppressWarnings("rawtypes")
static final PublishSubscription[] TERMINATED = new PublishSubscription[0];
/** An empty subscribers array to avoid allocating it all the time. */
@SuppressWarnings("rawtypes")
static final PublishSubscription[] EMPTY = new PublishSubscription[0];
/** The array of currently subscribed subscribers. */
final AtomicReference<PublishSubscription<T>[]> subscribers;
/** The error, write before terminating and read after checking subscribers. */
Throwable error;
/**
* Constructs a PublishProcessor.
* @param <T> the value type
* @return the new PublishProcessor
*/
@CheckReturnValue
public static <T> PublishProcessor<T> create() {
return new PublishProcessor<T>();
}
/**
* Constructs a PublishProcessor.
* @since 2.0
*/
@SuppressWarnings("unchecked")
PublishProcessor() {
subscribers = new AtomicReference<PublishSubscription<T>[]>(EMPTY);
}
@Override
public void subscribeActual(Subscriber<? super T> t) {
PublishSubscription<T> ps = new PublishSubscription<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.isCancelled()) {
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(PublishSubscription<T> ps) {
for (;;) {
PublishSubscription<T>[] a = subscribers.get();
if (a == TERMINATED) {
return false;
}
int n = a.length;
@SuppressWarnings("unchecked")
PublishSubscription<T>[] b = new PublishSubscription[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(PublishSubscription<T> ps) {
for (;;) {
PublishSubscription<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;
}
PublishSubscription<T>[] b;
if (n == 1) {
b = EMPTY;
} else {
b = new PublishSubscription[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(Subscription s) {
if (subscribers.get() == TERMINATED) {
s.cancel();
return;
}
// PublishSubject doesn't bother with request coordination.
s.request(Long.MAX_VALUE);
}
@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 (PublishSubscription<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 (PublishSubscription<T> s : subscribers.getAndSet(TERMINATED)) {
s.onError(t);
}
}
@SuppressWarnings("unchecked")
@Override
public void onComplete() {
if (subscribers.get() == TERMINATED) {
return;
}
for (PublishSubscription<T> s : subscribers.getAndSet(TERMINATED)) {
s.onComplete();
}
}
/**
* Tries to emit the item to all currently subscribed Subscribers if all of them
* has requested some value, returns false otherwise.
* <p>
* This method should be called in a sequential manner just like the onXXX methods
* of the PublishProcessor.
* <p>
* Calling with null will terminate the PublishProcessor and a NullPointerException
* is signalled to the Subscribers.
* @param t the item to emit, not null
* @return true if the item was emitted to all Subscribers
* @since 2.0.8 - experimental
*/
@Experimental
public boolean offer(T t) {
if (t == null) {
onError(new NullPointerException("onNext called with null. Null values are generally not allowed in 2.x operators and sources."));
return true;
}
PublishSubscription<T>[] array = subscribers.get();
for (PublishSubscription<T> s : array) {
if (s.isFull()) {
return false;
}
}
for (PublishSubscription<T> s : array) {
s.onNext(t);
}
return true;
}
@Override
public boolean hasSubscribers() {
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 PublishSubscription<T> extends AtomicLong implements Subscription {
private static final long serialVersionUID = 3562861878281475070L;
/** The actual subscriber. */
final Subscriber<? super T> actual;
/** The subject state. */
final PublishProcessor<T> parent;
/**
* Constructs a PublishSubscriber, wraps the actual subscriber and the state.
* @param actual the actual subscriber
* @param parent the parent PublishProcessor
*/
PublishSubscription(Subscriber<? super T> actual, PublishProcessor<T> parent) {
this.actual = actual;
this.parent = parent;
}
public void onNext(T t) {
long r = get();
if (r == Long.MIN_VALUE) {
return;
}
if (r != 0L) {
actual.onNext(t);
if (r != Long.MAX_VALUE) {
decrementAndGet();
}
} else {
cancel();
actual.onError(new MissingBackpressureException("Could not emit value due to lack of requests"));
}
}
public void onError(Throwable t) {
if (get() != Long.MIN_VALUE) {
actual.onError(t);
} else {
RxJavaPlugins.onError(t);
}
}
public void onComplete() {
if (get() != Long.MIN_VALUE) {
actual.onComplete();
}
}
@Override
public void request(long n) {
if (SubscriptionHelper.validate(n)) {
BackpressureHelper.addCancel(this, n);
}
}
@Override
public void cancel() {
if (getAndSet(Long.MIN_VALUE) != Long.MIN_VALUE) {
parent.remove(this);
}
}
public boolean isCancelled() {
return get() == Long.MIN_VALUE;
}
boolean isFull() {
return get() == 0L;
}
}
}