/**
* 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.functions.
ObjectHelper;
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="278" src="https://raw.github.com/wiki/ReactiveX/RxJava/images/rx-operators/PublishProcessor.png" alt="">
* <p>
* This processor does not have a public constructor by design; a new empty instance of this
* {@code PublishProcessor} can be created via the {@link #create()} method.
* <p>
* Since a {@code PublishProcessor} is a Reactive Streams {@code Processor} type,
* {@code null}s are not allowed (<a href="https://github.com/reactive-streams/reactive-streams-jvm#2.13">Rule 2.13</a>) as
* parameters to {@link #onNext(Object)} and {@link #onError(Throwable)}. Such calls will result in a
* {@link NullPointerException} being thrown and the processor's state is not changed.
* <p>
* {@code PublishProcessor} is a {@link io.reactivex.Flowable} as well as a {@link FlowableProcessor},
* however, it does not coordinate backpressure between different subscribers and between an
* upstream source and a subscriber. If an upstream item is received via {@link #onNext(Object)}, if
* a subscriber is not ready to receive an item, that subscriber is terminated via a {@link MissingBackpressureException}.
* To avoid this case, use {@link #offer(Object)} and retry sometime later if it returned false.
* The {@code PublishProcessor}'s {@link Subscriber}-side consumes items in an unbounded manner.
* <p>
* For a multicasting processor type that also coordinates between the downstream {@code Subscriber}s and the upstream
* source as well, consider using {@link MulticastProcessor}.
* <p>
* When this {@code PublishProcessor} is terminated via {@link #onError(Throwable)} or {@link #onComplete()},
* late {@link Subscriber}s only receive the respective terminal event.
* <p>
* Unlike a {@link BehaviorProcessor}, a {@code PublishProcessor} doesn't retain/cache items, therefore, a new
* {@code Subscriber} won't receive any past items.
* <p>
* Even though {@code PublishProcessor} implements the {@link Subscriber} interface, calling
* {@code onSubscribe} is not required (<a href="https://github.com/reactive-streams/reactive-streams-jvm#2.12">Rule 2.12</a>)
* if the processor is used as a standalone source. However, calling {@code onSubscribe}
* after the {@code PublishProcessor} reached its terminal state will result in the
* given {@link Subscription} being canceled immediately.
* <p>
* Calling {@link #onNext(Object)}, {@link #offer(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 {@link FlowableProcessor}s
* provides such serialization and also protects against reentrance (i.e., when a downstream {@code Subscriber}
* consuming this processor also wants to call {@link #onNext(Object)} on this processor recursively).
* Note that serializing over {@link #offer(Object)} is not supported through {@code toSerialized()} because it is a method
* available on the {@code PublishProcessor} and {@code BehaviorProcessor} classes only.
* <p>
* This {@code PublishProcessor} supports the standard state-peeking methods {@link #hasComplete()}, {@link #hasThrowable()},
* {@link #getThrowable()} and {@link #hasSubscribers()}.
* <dl>
* <dt><b>Backpressure:</b></dt>
* <dd>The processor does not coordinate backpressure for its subscribers and implements a weaker {@code onSubscribe} which
* calls requests Long.MAX_VALUE from the incoming Subscriptions. This makes it possible to subscribe the {@code PublishProcessor}
* to multiple sources (note on serialization though) unlike the standard {@code Subscriber} contract. Child subscribers, however, are not overflown but receive an
* {@link IllegalStateException} in case their requested amount is zero.</dd>
* <dt><b>Scheduler:</b></dt>
* <dd>{@code PublishProcessor} does not operate by default on a particular {@link io.reactivex.Scheduler} and
* the {@code Subscriber}s get notified on the thread the respective {@code onXXX} methods were invoked.</dd>
* <dt><b>Error handling:</b></dt>
* <dd>When the {@link #onError(Throwable)} is called, the {@code PublishProcessor} enters into a terminal state
* and emits the same {@code Throwable} instance to the last set of {@code Subscriber}s. During this emission,
* if one or more {@code Subscriber}s cancel their respective {@code Subscription}s, the
* {@code Throwable} is delivered to the global error handler via
* {@link io.reactivex.plugins.RxJavaPlugins#onError(Throwable)} (multiple times if multiple {@code Subscriber}s
* cancel at once).
* If there were no {@code Subscriber}s subscribed to this {@code PublishProcessor} when the {@code onError()}
* was called, the global error handler is not invoked.
* </dd>
* </dl>
*
* Example usage:
* <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.
* @see MulticastProcessor
*/
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
@
NonNull
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
protected 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 this processor has terminated.
* @param ps the subscriber to add
* @return true if successful, false if this processor 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 this processor.
* @param ps the subscription wrapping a subscriber 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;
}
// PublishProcessor doesn't bother with request coordination.
s.
request(
Long.
MAX_VALUE);
}
@
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.");
for (
PublishSubscription<T>
s :
subscribers.
get()) {
s.
onNext(
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;
}
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.
* <p>History: 2.0.8 - experimental
* @param t the item to emit, not null
* @return true if the item was emitted to all Subscribers
* @since 2.2
*/
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
@
Nullable
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>
downstream;
/** The parent processor servicing this subscriber. */
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.
downstream =
actual;
this.
parent =
parent;
}
public void
onNext(T
t) {
long
r =
get();
if (
r ==
Long.
MIN_VALUE) {
return;
}
if (
r != 0L) {
downstream.
onNext(
t);
BackpressureHelper.
producedCancel(this, 1);
} else {
cancel();
downstream.
onError(new
MissingBackpressureException("Could not emit value due to lack of requests"));
}
}
public void
onError(
Throwable t) {
if (
get() !=
Long.
MIN_VALUE) {
downstream.
onError(
t);
} else {
RxJavaPlugins.
onError(
t);
}
}
public void
onComplete() {
if (
get() !=
Long.
MIN_VALUE) {
downstream.
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;
}
}
}