FluxRefCountGrace.java

/*
 * Copyright (c) 2011-2017 Pivotal Software Inc, All Rights Reserved.
 *
 * 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 reactor.core.publisher;

import java.time.Duration;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicIntegerFieldUpdater;
import java.util.concurrent.atomic.AtomicReferenceFieldUpdater;
import java.util.function.Consumer;

import org.reactivestreams.Subscriber;
import org.reactivestreams.Subscription;
import reactor.core.Disposable;
import reactor.core.Disposables;
import reactor.core.Disposables.SequentialDisposable;
import reactor.core.Fuseable;
import reactor.core.Scannable;
import reactor.core.scheduler.Scheduler;

/**
 * @author Simon Baslé
 * @author David Karnok
 */
//adapted from RxJava2Extensions: https://github.com/akarnokd/RxJava2Extensions/blob/master/src/main/java/hu/akarnokd/rxjava2/operators/FlowableRefCountTimeout.java
final class FluxRefCountGrace<T> extends Flux<T> implements Scannable, Fuseable {

	final ConnectableFlux<T> source;
	final int                n;
	final Duration           gracePeriod;
	final Scheduler          scheduler;

	RefConnection connection;

	volatile Disposable timeoutTask;
	static final AtomicReferenceFieldUpdater<FluxRefCountGrace, Disposable> TIMEOUT_TASK =
			AtomicReferenceFieldUpdater.newUpdater(FluxRefCountGrace.class, Disposable.class, "timeoutTask");

	FluxRefCountGrace(ConnectableFlux<T> source, int n, Duration gracePeriod, Scheduler scheduler) {
		this.source = source;
		this.n = n;
		this.gracePeriod = gracePeriod;
		this.scheduler = scheduler;
	}


	@Override
	public int getPrefetch() {
		return source.getPrefetch();
	}

	@Override
	public Object scan(Attr key) {
		switch (key){
			case PREFETCH:
				return getPrefetch();
			case PARENT:
				return source;
		}
		return null;
	}

	@Override
	public void subscribe(Subscriber<? super T> s) {
		for (; ; ) {
			RefConnection conn;

			boolean connect = false;
			synchronized (this) {
				conn = connection;
				if (conn == null || conn.terminated) {
					conn = new RefConnection(this);
					connection = conn;
				}

				long c = conn.subscriberCount;
				if (c == 0L && conn.timer != null) {
					conn.timer.dispose();
				}
				conn.subscriberCount = c + 1;
				if (!conn.connected && c + 1 == n) {
					connect = true;
					conn.connected = true;
				}
			}

			source.subscribe(new RefCountSubscriber<>(s, this, conn));

			if (connect) {
				source.connect(conn);
			}

			break;
		}
	}

	void cancel(RefConnection rc) {
		SequentialDisposable sd;
		synchronized (this) {
			if (rc.terminated) {
				return;
			}
			long c = rc.subscriberCount - 1;
			rc.subscriberCount = c;
			if (c != 0L || !rc.connected) {
				return;
			}
			if (gracePeriod.isZero()) {
				timeout(rc);
				return;
			}
			sd = new SequentialDisposable();
			rc.timer = sd;
		}

		sd.replace(scheduler.schedule(rc, gracePeriod.toMillis(), TimeUnit.MILLISECONDS));
	}

	void terminated(RefConnection rc) {
		synchronized (this) {
			if (!rc.terminated) {
				rc.terminated = true;
				connection = null;
			}
		}
	}

	void timeout(RefConnection rc) {
		synchronized (this) {
			if (rc.subscriberCount == 0 && rc == connection) {
				Disposables.dispose(RefConnection.SOURCE_DISCONNECTOR, rc);
				if (source instanceof Disposable) {
					((Disposable) source).dispose();
				}
				connection = null;
			}
		}
	}

	static final class RefConnection implements Runnable, Consumer<Disposable> {

		final FluxRefCountGrace<?> parent;

		Disposable timer;
		long       subscriberCount;
		boolean    connected;
		boolean    terminated;

		volatile Disposable sourceDisconnector;
		static final AtomicReferenceFieldUpdater<RefConnection, Disposable> SOURCE_DISCONNECTOR =
				AtomicReferenceFieldUpdater.newUpdater(RefConnection.class, Disposable.class, "sourceDisconnector");

		RefConnection(FluxRefCountGrace<?> parent) {
			this.parent = parent;
		}

		@Override
		public void run() {
			parent.timeout(this);
		}

		@Override
		public void accept(Disposable t) {
			Disposables.replace(SOURCE_DISCONNECTOR, this, t);
		}
	}

	static final class RefCountSubscriber<T> implements Subscriber<T>, Subscription {

		final Subscriber<? super T> actual;

		final FluxRefCountGrace<T> parent;

		final RefConnection connection;

		Subscription upstream;

		volatile int parentDone;
		static final AtomicIntegerFieldUpdater<RefCountSubscriber> PARENT_DONE =
				AtomicIntegerFieldUpdater.newUpdater(RefCountSubscriber.class, "parentDone");

		RefCountSubscriber(Subscriber<? super T> actual, FluxRefCountGrace<T> parent,
				RefConnection connection) {
			this.actual = actual;
			this.parent = parent;
			this.connection = connection;
		}

		@Override
		public void onNext(T t) {
			actual.onNext(t);
		}

		@Override
		public void onError(Throwable t) {
			actual.onError(t);
			if (PARENT_DONE.compareAndSet(this, 0, 1)) {
				parent.terminated(connection);
			}
		}

		@Override
		public void onComplete() {
			actual.onComplete();
			if (PARENT_DONE.compareAndSet(this, 0, 1)) {
				parent.terminated(connection);
			}
		}

		@Override
		public void request(long n) {
			upstream.request(n);
		}

		@Override
		public void cancel() {
			upstream.cancel();
			if (PARENT_DONE.compareAndSet(this, 0, 1)) {
				parent.cancel(connection);
			}
		}

		@Override
		public void onSubscribe(Subscription s) {
			if (Operators.validate(upstream, s)) {
				this.upstream = s;

				actual.onSubscribe(this);
			}
		}
	}
}