hu.akarnokd.rxjava2.subjects.nbp.NbpUnicastSubject Maven / Gradle / Ivy
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/**
* Copyright 2015 David Karnok and Netflix, Inc.
*
* 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 hu.akarnokd.rxjava2.subjects.nbp;
import java.util.Queue;
import java.util.concurrent.atomic.*;
import hu.akarnokd.rxjava2.disposables.Disposable;
import hu.akarnokd.rxjava2.internal.disposables.EmptyDisposable;
import hu.akarnokd.rxjava2.internal.queue.SpscLinkedArrayQueue;
/**
* Subject that allows only a single Subscriber to subscribe to it during its lifetime.
*
* This subject buffers notifications and replays them to the Subscriber as requested.
*
*
This subject holds an unbounded internal buffer.
*
*
If more than one Subscriber attempts to subscribe to this Subject, they
* will receive an IllegalStateException if this Subject hasn't terminated yet,
* or the Subscribers receive the terminal event (error or completion) if this
* Subject has terminated.
*
* @param the value type unicasted
*/
public final class NbpUnicastSubject extends NbpSubject {
/**
* Creates an UnicastSubject with an internal buffer capacity hint 16.
* @param the value type
* @return an UnicastSubject instance
*/
public static NbpUnicastSubject create() {
return create(16);
}
/**
* Creates an UnicastSubject with the given internal buffer capacity hint.
* @param the value type
* @param capacityHint the hint to size the internal unbounded buffer
* @return an UnicastSubject instance
*/
public static NbpUnicastSubject create(int capacityHint) {
return create(capacityHint, null);
}
/**
* Creates an UnicastSubject with the given internal buffer capacity hint and a callback for
* the case when the single Subscriber cancels its subscription.
*
* The callback, if not null, is called exactly once and
* non-overlapped with any active replay.
*
* @param the value type
* @param capacityHint the hint to size the internal unbounded buffer
* @param onCancelled the optional callback
* @return an UnicastSubject instance
*/
public static NbpUnicastSubject create(int capacityHint, Runnable onCancelled) {
State state = new State(capacityHint, onCancelled);
return new NbpUnicastSubject(state);
}
/** The subject state. */
final State state;
/**
* Constructs the Observable base class.
* @param state the subject state
*/
protected NbpUnicastSubject(State state) {
super(state);
this.state = state;
}
// TODO may need to have a direct WIP field to avoid clashing on the object header
/** Pads the WIP counter. */
static abstract class StatePad0 extends AtomicInteger {
/** */
private static final long serialVersionUID = 7779228232971173701L;
/** Cache line padding 1. */
volatile long p1a, p2a, p3a, p4a, p5a, p6a, p7a;
/** Cache line padding 2. */
volatile long p8a, p9a, p10a, p11a, p12a, p13a, p14a, p15a;
}
/** The state of the UnicastSubject. */
static final class State extends StatePad0 implements NbpOnSubscribe, Disposable, NbpSubscriber {
/** */
private static final long serialVersionUID = 5058617037583835632L;
/** The queue that buffers the source events. */
final Queue queue;
/** The single subscriber. */
volatile NbpSubscriber subscriber;
/** Updater to the field subscriber. */
@SuppressWarnings("rawtypes")
static final AtomicReferenceFieldUpdater SUBSCRIBER =
AtomicReferenceFieldUpdater.newUpdater(State.class, NbpSubscriber.class, "subscriber");
/** Indicates the single subscriber has cancelled. */
volatile boolean cancelled;
/** Indicates the source has terminated. */
volatile boolean done;
/**
* The terminal error if not null.
* Must be set before writing to done and read after done == true.
*/
Throwable error;
/** Set to 1 atomically for the first and only Subscriber. */
volatile int once;
/** Updater to field once. */
@SuppressWarnings("rawtypes")
static final AtomicIntegerFieldUpdater ONCE =
AtomicIntegerFieldUpdater.newUpdater(State.class, "once");
/**
* Called when the Subscriber has called cancel.
* This allows early termination for those who emit into this
* subject so that they can stop immediately
*/
Runnable onCancelled;
/**
* Constructs the state with the given capacity and optional cancellation callback.
* @param capacityHint the capacity hint for the internal buffer
* @param onCancelled the optional cancellation callback
*/
public State(int capacityHint, Runnable onCancelled) {
this.onCancelled = onCancelled;
queue = new SpscLinkedArrayQueue(capacityHint);
}
@Override
public void accept(NbpSubscriber s) {
if (once == 0 && ONCE.compareAndSet(this, 0, 1)) {
s.onSubscribe(this);
SUBSCRIBER.lazySet(this, s); // full barrier in drain
drain();
} else {
s.onSubscribe(EmptyDisposable.INSTANCE);
if (done) {
Throwable e = error;
if (e != null) {
s.onError(e);
} else {
s.onComplete();
}
} else {
s.onError(new IllegalStateException("Only a single subscriber allowed."));
}
}
}
@Override
public void dispose() {
if (!cancelled) {
cancelled = true;
if (getAndIncrement() == 0) {
clear(queue);
}
}
}
void notifyOnCancelled() {
Runnable r = onCancelled;
onCancelled = null;
if (r != null) {
r.run();
}
}
/**
* Clears the subscriber and the queue.
* @param q the queue reference (avoid re-reading instance field).
*/
void clear(Queue q) {
SUBSCRIBER.lazySet(this, null);
q.clear();
notifyOnCancelled();
}
@Override
public void onSubscribe(Disposable s) {
if (done || cancelled) {
s.dispose();
}
}
@Override
public void onNext(T t) {
if (done || cancelled) {
return;
}
if (t == null) {
onError(new NullPointerException());
return;
}
queue.offer(t);
drain();
}
@Override
public void onError(Throwable t) {
if (done || cancelled) {
return;
}
if (t == null) {
t = new NullPointerException();
}
error = t;
done = true;
drain();
}
@Override
public void onComplete() {
if (done || cancelled) {
return;
}
done = true;
drain();
}
void drain() {
if (getAndIncrement() != 0) {
return;
}
final Queue q = queue;
NbpSubscriber a = subscriber;
int missed = 1;
for (;;) {
if (cancelled) {
clear(q);
notifyOnCancelled();
return;
}
if (a != null) {
boolean d = done;
boolean empty = q.isEmpty();
if (d && empty) {
SUBSCRIBER.lazySet(this, null);
Throwable ex = error;
if (ex != null) {
a.onError(ex);
} else {
a.onComplete();
}
return;
}
for (;;) {
if (cancelled) {
clear(q);
notifyOnCancelled();
return;
}
d = done;
T v = queue.poll();
empty = v == null;
if (d && empty) {
SUBSCRIBER.lazySet(this, null);
Throwable ex = error;
if (ex != null) {
a.onError(ex);
} else {
a.onComplete();
}
return;
}
if (empty) {
break;
}
a.onNext(v);
}
}
missed = addAndGet(-missed);
if (missed == 0) {
break;
}
if (a == null) {
a = subscriber;
}
}
}
}
@Override
public void onSubscribe(Disposable s) {
state.onSubscribe(s);
}
@Override
public void onNext(T t) {
state.onNext(t);
}
@Override
public void onError(Throwable t) {
state.onError(t);
}
@Override
public void onComplete() {
state.onComplete();
}
@Override
public boolean hasSubscribers() {
return state.subscriber != null;
}
@Override
public Throwable getThrowable() {
State s = state;
if (s.done) {
return s.error;
}
return null;
}
@Override
public boolean hasThrowable() {
State s = state;
return s.done && s.error != null;
}
@Override
public boolean hasComplete() {
State s = state;
return s.done && s.error == null;
}
@Override
public boolean hasValue() {
return false;
}
@Override
public T getValue() {
return null;
}
@Override
public T[] getValues(T[] array) {
if (array.length != 0) {
array[0] = null;
}
return array;
}
}