/*
* Copyright 2014 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 io.reactivex.netty.protocol.http;
import io.netty.buffer.ByteBuf;
import io.netty.util.ReferenceCountUtil;
import io.reactivex.netty.protocol.http.client.HttpClientResponse;
import io.reactivex.netty.protocol.http.server.HttpServerRequest;
import rx.Observable;
import rx.Observer;
import rx.Scheduler;
import rx.Subscriber;
import rx.functions.Action0;
import rx.functions.Action1;
import rx.internal.operators.NotificationLite;
import rx.observers.Subscribers;
import rx.schedulers.Schedulers;
import rx.subjects.Subject;
import rx.subscriptions.Subscriptions;
import java.util.concurrent.ConcurrentLinkedQueue;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicIntegerFieldUpdater;
import java.util.concurrent.atomic.AtomicReferenceFieldUpdater;
/**
* A {@link Subject} implementation to be used by {@link HttpClientResponse} and {@link HttpServerRequest}.
*
* <h2>Unicast</h2>
* This implementation allows a single subscription as this buffers the content till subscription to solve the issue
* described in <a href="https://github.com/Netflix/RxNetty/issues/206">this github issue</a>.
* If we allow multiple subscription and still maintain it as a cold observable i.e. which re-runs the stream on every
* subscription, we loose the control on the scope of this {@link Observable} as any code can hold the reference to
* this {@link Observable} at any point in time and hence subscribe to it at any time. This will eventually increase
* memory consumption as we will hold on to the content buffers for more time than required.
*
* <h2>Multicast option</h2>
* If at all it is required to allow multiple subscriptions to this {@link Subject} one should use a
* {@link Observable#publish()} operator.
*
* <h2>Buffering</h2>
* This subject will buffer all content till the first (one and only) subscriber arrives.
* In cases, when there are no subscriptions, this buffer may be held till infinity and hence can cause a memory leak in
* case of netty's {@link ByteBuf} which needs to be released explicitly.
* In order to avoid this leak, this subject provides a "no subscription timeout" which disposes this subject (calling
* {@link #disposeIfNotSubscribed()} if it does not get a subscription in the configured timeout duration.
*
* The buffer is only utilized if there are any items emitted to this subject before a subscription arrives. After a
* subscription arrives, this subject becomes a pass through i.e. it does not buffer before sending the notifications.
*
* This implementation is inspired by
* <a href="https://github.com/Netflix/RxJava/blob/master/rxjava-core/src/main/java/rx/internal/operators/BufferUntilSubscriber.java">RxJava's BufferUntilSubscriber</a>
* @author Nitesh Kant
*/
public final class UnicastContentSubject<T> extends Subject<T, T> {
private final State<T> state;
private volatile Observable<Long> timeoutScheduler;
private UnicastContentSubject(State<T> state) {
super(new OnSubscribeAction<T>(state));
this.state = state;
timeoutScheduler = Observable.empty(); // No timeout.
}
private UnicastContentSubject(final State<T> state, long noSubscriptionTimeout, TimeUnit timeUnit,
Scheduler scheduler) {
super(new OnSubscribeAction<T>(state));
this.state = state;
timeoutScheduler = Observable.interval(noSubscriptionTimeout, timeUnit, scheduler).take(1); // Started when content arrives.
}
/**
* Creates a new {@link UnicastContentSubject} without a no subscription timeout.
* <b>This can cause a memory leak in case no one ever subscribes to this subject.</b> See
* {@link UnicastContentSubject} for details.
*
* @param onUnsubscribe An action to be invoked when the sole subscriber to this {@link Subject} unsubscribes.
* @param <T> The type emitted and received by this subject.
*
* @return The new instance of {@link UnicastContentSubject}
*/
public static <T> UnicastContentSubject<T> createWithoutNoSubscriptionTimeout(Action0 onUnsubscribe) {
State<T> state = new State<T>(onUnsubscribe);
return new UnicastContentSubject<T>(state);
}
/**
* Creates a new {@link UnicastContentSubject} without a no subscription timeout.
* <b>This can cause a memory leak in case no one ever subscribes to this subject.</b> See
* {@link UnicastContentSubject} for details.
*
* @param <T> The type emitted and received by this subject.
*
* @return The new instance of {@link UnicastContentSubject}
*/
public static <T> UnicastContentSubject<T> createWithoutNoSubscriptionTimeout() {
return createWithoutNoSubscriptionTimeout(null);
}
public static <T> UnicastContentSubject<T> create(long noSubscriptionTimeout, TimeUnit timeUnit) {
return create(noSubscriptionTimeout, timeUnit, (Action0)null);
}
public static <T> UnicastContentSubject<T> create(long noSubscriptionTimeout, TimeUnit timeUnit,
Action0 onUnsubscribe) {
return create(noSubscriptionTimeout, timeUnit, Schedulers.computation(), onUnsubscribe);
}
public static <T> UnicastContentSubject<T> create(long noSubscriptionTimeout, TimeUnit timeUnit,
Scheduler timeoutScheduler) {
return create(noSubscriptionTimeout, timeUnit, timeoutScheduler, null);
}
public static <T> UnicastContentSubject<T> create(long noSubscriptionTimeout, TimeUnit timeUnit,
Scheduler timeoutScheduler, Action0 onUnsubscribe) {
State<T> state = new State<T>(onUnsubscribe);
return new UnicastContentSubject<T>(state, noSubscriptionTimeout, timeUnit, timeoutScheduler);
}
/**
* This will eagerly dispose this {@link Subject} without waiting for the no subscription timeout period,
* if configured.
*
* This must be invoked when the caller is sure that no one will subscribe to this subject. Any subscriber after
* this call will receive an error that the subject is disposed.
*
* @return {@code true} if the subject was disposed by this call (if and only if there was no subscription).
*/
public boolean disposeIfNotSubscribed() {
if (state.casState(State.STATES.UNSUBSCRIBED, State.STATES.DISPOSED)) {
Subscriber<T> noOpSub = new PassThruObserver<T>(Subscribers.empty(), state); // Any buffering post buffer draining must not be lying in the buffer
state.buffer.sendAllNotifications(noOpSub); // It is important to empty the buffer before setting the observer.
// If not done, there can be two threads draining the buffer
// (PassThroughObserver on any notification) and this thread.
state.setObserverRef(noOpSub); // All future notifications are not sent anywhere.
if (null != state.onUnsubscribe) {
state.onUnsubscribe.call(); // Since this is an inline/sync call, if this throws an error, it gets thrown to the caller.
}
return true;
}
return false;
}
public void updateTimeoutIfNotScheduled(long noSubscriptionTimeout, TimeUnit timeUnit) {
if (0 == state.timeoutScheduled) {
timeoutScheduler = Observable.interval(noSubscriptionTimeout, timeUnit).take(1);
}
}
/** The common state. */
private static final class State<T> {
private final Action0 onUnsubscribe;
public State() {
this(null);
}
public State(Action0 onUnsubscribe) {
this.onUnsubscribe = onUnsubscribe;
}
/**
* Following are the only possible state transitions:
* UNSUBSCRIBED -> SUBSCRIBED
* UNSUBSCRIBED -> DISPOSED
*/
private enum STATES {
UNSUBSCRIBED /*Initial*/, SUBSCRIBED /*Terminal state*/, DISPOSED/*Terminal state*/
}
private volatile int state = STATES.UNSUBSCRIBED.ordinal(); /*Values are the ordinals of STATES enum*/
/** Following Observers are associated with the states:
* UNSUBSCRIBED => {@link BufferedObserver}
* SUBSCRIBED => {@link PassThruObserver}
* DISPOSED => {@link Subscribers#empty()}
*/
private volatile Observer<? super T> observerRef = new BufferedObserver();
@SuppressWarnings("unused")private volatile int timeoutScheduled; // Boolean
/**
* The only buffer associated with this state. All notifications go to this buffer if no one has subscribed and
* the {@link UnicastContentSubject} instance is not disposed.
*/
private final ByteBufAwareBuffer<T> buffer = new ByteBufAwareBuffer<T>();
/** Field updater for observerRef. */
@SuppressWarnings("rawtypes")
private static final AtomicReferenceFieldUpdater<State, Observer> OBSERVER_UPDATER
= AtomicReferenceFieldUpdater.newUpdater(State.class, Observer.class, "observerRef");
/** Field updater for state. */
@SuppressWarnings("rawtypes")
private static final AtomicIntegerFieldUpdater<State> STATE_UPDATER
= AtomicIntegerFieldUpdater.newUpdater(State.class, "state");
/** Field updater for timeoutScheduled. */
@SuppressWarnings("rawtypes")
private static final AtomicIntegerFieldUpdater<State> TIMEOUT_SCHEDULED_UPDATER
= AtomicIntegerFieldUpdater.newUpdater(State.class, "timeoutScheduled");
public boolean casState(STATES expected, STATES next) {
return STATE_UPDATER.compareAndSet(this, expected.ordinal(), next.ordinal());
}
public void setObserverRef(Observer<? super T> o) { // Guarded by casState()
observerRef = o;
}
public boolean casObserverRef(Observer<? super T> expected, Observer<? super T> next) {
return OBSERVER_UPDATER.compareAndSet(this, expected, next);
}
public boolean casTimeoutScheduled() {
return TIMEOUT_SCHEDULED_UPDATER.compareAndSet(this, 0, 1);
}
/**
* The default subscriber when the enclosing state is created.
*/
private final class BufferedObserver extends Subscriber<T> {
private final NotificationLite<Object> nl = NotificationLite.instance();
@Override
public void onCompleted() {
buffer.add(nl.completed());
}
@Override
public void onError(Throwable e) {
buffer.add(nl.error(e));
}
@Override
public void onNext(T t) {
buffer.add(nl.next(t));
}
}
}
private static final class OnSubscribeAction<T> implements OnSubscribe<T> {
private final State<T> state;
public OnSubscribeAction(State<T> state) {
this.state = state;
}
@Override
public void call(final Subscriber<? super T> subscriber) {
if (state.casState(State.STATES.UNSUBSCRIBED, State.STATES.SUBSCRIBED)) {
// drain queued notifications before subscription
// we do this here before PassThruObserver so the consuming thread can do this before putting itself in
// the line of the producer
state.buffer.sendAllNotifications(subscriber);
// register real observer for pass-thru ... and drain any further events received on first notification
state.setObserverRef(new PassThruObserver<T>(subscriber, state));
subscriber.add(Subscriptions.create(new Action0() {
@Override
public void call() {
if (null != state.onUnsubscribe) {
state.onUnsubscribe.call();
}
state.setObserverRef(Subscribers.empty());
}
}));
} else if(State.STATES.SUBSCRIBED.ordinal() == state.state) {
subscriber.onError(new IllegalStateException("Content can only have one subscription. Use Observable.publish() if you want to multicast."));
} else if(State.STATES.DISPOSED.ordinal() == state.state) {
subscriber.onError(new IllegalStateException("Content stream is already disposed."));
}
}
}
@Override
public void onCompleted() {
state.observerRef.onCompleted();
}
@Override
public void onError(Throwable e) {
state.observerRef.onError(e);
}
@Override
public void onNext(T t) {
state.observerRef.onNext(t);
if (state.casTimeoutScheduled()) {// Schedule timeout once.
timeoutScheduler.subscribe(new Action1<Long>() { // Schedule timeout after the first content arrives.
@Override
public void call(Long aLong) {
disposeIfNotSubscribed();
}
});
}
}
/**
* This is a temporary observer between buffering and the actual that gets into the line of notifications
* from the producer and will drain the queue of any items received during the race of the initial drain and
* switching this.
*
* It will then immediately swap itself out for the actual (after a single notification), but since this is
* now being done on the same producer thread no further buffering will occur.
*/
private static final class PassThruObserver<T> extends Subscriber<T> {
private final Observer<? super T> actual;
// this assumes single threaded synchronous notifications (the Rx contract for a single Observer)
private final ByteBufAwareBuffer<T> buffer; // Same buffer instance from the original BufferedObserver.
private final State<T> state;
PassThruObserver(Observer<? super T> actual, State<T> state) {
this.actual = actual;
buffer = state.buffer;
this.state = state;
}
@Override
public void onCompleted() {
drainIfNeededAndSwitchToActual();
actual.onCompleted();
}
@Override
public void onError(Throwable e) {
drainIfNeededAndSwitchToActual();
actual.onError(e);
}
@Override
public void onNext(T t) {
drainIfNeededAndSwitchToActual();
actual.onNext(t);
}
private void drainIfNeededAndSwitchToActual() {
buffer.sendAllNotifications(this);
// now we can safely change over to the actual and get rid of the pass-thru
// but only if not unsubscribed
state.casObserverRef(this, actual);
}
}
private static final class ByteBufAwareBuffer<T> {
private final ConcurrentLinkedQueue<Object> actual = new ConcurrentLinkedQueue<Object>();
private final NotificationLite<T> nl = NotificationLite.instance();
private void add(Object toAdd) {
ReferenceCountUtil.retain(toAdd); // Released when the notification is sent.
actual.add(toAdd);
}
public void sendAllNotifications(Subscriber<? super T> subscriber) {
Object notification; // Can be onComplete notification, onError notification or just the actual "T".
while ((notification = actual.poll()) != null) {
try {
nl.accept(subscriber, notification);
} finally {
ReferenceCountUtil.release(notification); // If it is the actual T for onNext and is a ByteBuf, it will be released.
}
}
}
}
}