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/*
 * Copyright (c) 2016-2021 VMware Inc. or its affiliates, 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
 *
 *   https://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.util.Objects;
import java.util.Queue;
import java.util.concurrent.atomic.AtomicIntegerFieldUpdater;
import java.util.concurrent.atomic.AtomicLongFieldUpdater;
import java.util.concurrent.atomic.AtomicReferenceFieldUpdater;
import java.util.function.Consumer;
import java.util.stream.Stream;

import org.reactivestreams.Subscription;

import reactor.core.CoreSubscriber;
import reactor.core.Disposable;
import reactor.core.Exceptions;
import reactor.core.Fuseable;
import reactor.core.Scannable;
import reactor.core.publisher.Sinks.EmitResult;
import reactor.util.annotation.Nullable;
import reactor.util.concurrent.Queues;
import reactor.util.context.Context;

/**
 * A Processor implementation that takes a custom queue and allows
 * only a single subscriber. UnicastProcessor allows multiplexing of the events which
 * means that it supports multiple producers and only one consumer.
 * However, it should be noticed that multi-producer case is only valid if appropriate
 * Queue
 * is provided. Otherwise, it could break
 * Reactive Streams Spec if Publishers
 * publish on different threads.
 *
 * 

* *

* *
*
* *

* Note: UnicastProcessor does not respect the actual subscriber's * demand as it is described in * Reactive Streams Spec. However, * UnicastProcessor embraces configurable Queue internally which allows enabling * backpressure support and preventing of consumer's overwhelming. * * Hence, interaction model between producers and UnicastProcessor will be PUSH * only. In opposite, interaction model between UnicastProcessor and consumer will be * PUSH-PULL as defined in * Reactive Streams Spec. * * In the case when upstream's signals overflow the bound of internal Queue, * UnicastProcessor will fail with signaling onError( * {@literal reactor.core.Exceptions.OverflowException}). * *

* *

*

* *
*
* *

* Note: The implementation keeps the order of signals. That means that in * case of terminal signal (completion or error signals) it will be postponed * until all of the previous signals has been consumed. *

* *

*

* * @param the input and output type * @deprecated to be removed in 3.5, prefer clear cut usage of {@link Sinks} through * variations under {@link reactor.core.publisher.Sinks.UnicastSpec Sinks.many().unicast()}. */ @Deprecated public final class UnicastProcessor extends FluxProcessor implements Fuseable.QueueSubscription, Fuseable, InnerOperator, InternalManySink { /** * Create a new {@link UnicastProcessor} that will buffer on an internal queue in an * unbounded fashion. * * @param the relayed type * @return a unicast {@link FluxProcessor} * @deprecated use {@link Sinks.UnicastSpec#onBackpressureBuffer() Sinks.many().unicast().onBackpressureBuffer()} * (or the unsafe variant if you're sure about external synchronization). To be removed in 3.5. */ @Deprecated public static UnicastProcessor create() { return new UnicastProcessor<>(Queues.unbounded().get()); } /** * Create a new {@link UnicastProcessor} that will buffer on a provided queue in an * unbounded fashion. * * @param queue the buffering queue * @param the relayed type * @return a unicast {@link FluxProcessor} * @deprecated use {@link Sinks.UnicastSpec#onBackpressureBuffer(Queue) Sinks.many().unicast().onBackpressureBuffer(queue)} * (or the unsafe variant if you're sure about external synchronization). To be removed in 3.5. */ @Deprecated public static UnicastProcessor create(Queue queue) { return new UnicastProcessor<>(Hooks.wrapQueue(queue)); } /** * Create a new {@link UnicastProcessor} that will buffer on a provided queue in an * unbounded fashion. * * @param queue the buffering queue * @param endcallback called on any terminal signal * @param the relayed type * @return a unicast {@link FluxProcessor} * @deprecated use {@link Sinks.UnicastSpec#onBackpressureBuffer(Queue, Disposable) Sinks.many().unicast().onBackpressureBuffer(queue, endCallback)} * (or the unsafe variant if you're sure about external synchronization). To be removed in 3.5. */ @Deprecated public static UnicastProcessor create(Queue queue, Disposable endcallback) { return new UnicastProcessor<>(Hooks.wrapQueue(queue), endcallback); } /** * Create a new {@link UnicastProcessor} that will buffer on a provided queue in an * unbounded fashion. * * @param queue the buffering queue * @param endcallback called on any terminal signal * @param onOverflow called when queue.offer return false and unicastProcessor is * about to emit onError. * @param the relayed type * * @return a unicast {@link FluxProcessor} * @deprecated use {@link Sinks.UnicastSpec#onBackpressureBuffer(Queue, Disposable) Sinks.many().unicast().onBackpressureBuffer(queue, endCallback)} * (or the unsafe variant if you're sure about external synchronization). The {@code onOverflow} callback is not * supported anymore. To be removed in 3.5. */ @Deprecated public static UnicastProcessor create(Queue queue, Consumer onOverflow, Disposable endcallback) { return new UnicastProcessor<>(Hooks.wrapQueue(queue), onOverflow, endcallback); } final Queue queue; final Consumer onOverflow; volatile Disposable onTerminate; @SuppressWarnings("rawtypes") static final AtomicReferenceFieldUpdater ON_TERMINATE = AtomicReferenceFieldUpdater.newUpdater(UnicastProcessor.class, Disposable.class, "onTerminate"); volatile boolean done; Throwable error; boolean hasDownstream; //important to not loose the downstream too early and miss discard hook, while having relevant hasDownstreams() volatile CoreSubscriber actual; volatile boolean cancelled; volatile int once; @SuppressWarnings("rawtypes") static final AtomicIntegerFieldUpdater ONCE = AtomicIntegerFieldUpdater.newUpdater(UnicastProcessor.class, "once"); volatile int wip; @SuppressWarnings("rawtypes") static final AtomicIntegerFieldUpdater WIP = AtomicIntegerFieldUpdater.newUpdater(UnicastProcessor.class, "wip"); volatile int discardGuard; @SuppressWarnings("rawtypes") static final AtomicIntegerFieldUpdater DISCARD_GUARD = AtomicIntegerFieldUpdater.newUpdater(UnicastProcessor.class, "discardGuard"); volatile long requested; @SuppressWarnings("rawtypes") static final AtomicLongFieldUpdater REQUESTED = AtomicLongFieldUpdater.newUpdater(UnicastProcessor.class, "requested"); boolean outputFused; public UnicastProcessor(Queue queue) { this.queue = Objects.requireNonNull(queue, "queue"); this.onTerminate = null; this.onOverflow = null; } public UnicastProcessor(Queue queue, Disposable onTerminate) { this.queue = Objects.requireNonNull(queue, "queue"); this.onTerminate = Objects.requireNonNull(onTerminate, "onTerminate"); this.onOverflow = null; } @Deprecated public UnicastProcessor(Queue queue, Consumer onOverflow, Disposable onTerminate) { this.queue = Objects.requireNonNull(queue, "queue"); this.onOverflow = Objects.requireNonNull(onOverflow, "onOverflow"); this.onTerminate = Objects.requireNonNull(onTerminate, "onTerminate"); } @Override public int getBufferSize() { return Queues.capacity(this.queue); } @Override public Stream inners() { return hasDownstream ? Stream.of(Scannable.from(actual)) : Stream.empty(); } @Override public Object scanUnsafe(Attr key) { if (Attr.ACTUAL == key) return actual(); if (Attr.BUFFERED == key) return queue.size(); if (Attr.PREFETCH == key) return Integer.MAX_VALUE; if (Attr.CANCELLED == key) return cancelled; //TERMINATED and ERROR covered in super return super.scanUnsafe(key); } @Override public void onComplete() { //no particular error condition handling for onComplete @SuppressWarnings("unused") EmitResult emitResult = tryEmitComplete(); } @Override public EmitResult tryEmitComplete() { if (done) { return EmitResult.FAIL_TERMINATED; } if (cancelled) { return EmitResult.FAIL_CANCELLED; } done = true; doTerminate(); drain(null); return Sinks.EmitResult.OK; } @Override public void onError(Throwable throwable) { emitError(throwable, Sinks.EmitFailureHandler.FAIL_FAST); } @Override public Sinks.EmitResult tryEmitError(Throwable t) { if (done) { return Sinks.EmitResult.FAIL_TERMINATED; } if (cancelled) { return EmitResult.FAIL_CANCELLED; } error = t; done = true; doTerminate(); drain(null); return EmitResult.OK; } @Override public void onNext(T t) { emitNext(t, Sinks.EmitFailureHandler.FAIL_FAST); } @Override public void emitNext(T value, Sinks.EmitFailureHandler failureHandler) { if (onOverflow == null) { InternalManySink.super.emitNext(value, failureHandler); return; } // TODO consider deprecating onOverflow and suggesting using a strategy instead InternalManySink.super.emitNext( value, (signalType, emission) -> { boolean shouldRetry = failureHandler.onEmitFailure(SignalType.ON_NEXT, emission); if (!shouldRetry) { switch (emission) { case FAIL_ZERO_SUBSCRIBER: case FAIL_OVERFLOW: try { onOverflow.accept(value); } catch (Throwable e) { Exceptions.throwIfFatal(e); emitError(e, Sinks.EmitFailureHandler.FAIL_FAST); } break; } } return shouldRetry; } ); } @Override public EmitResult tryEmitNext(T t) { if (done) { return EmitResult.FAIL_TERMINATED; } if (cancelled) { return EmitResult.FAIL_CANCELLED; } if (!queue.offer(t)) { return (once > 0) ? EmitResult.FAIL_OVERFLOW : EmitResult.FAIL_ZERO_SUBSCRIBER; } drain(t); return EmitResult.OK; } @Override public int currentSubscriberCount() { return hasDownstream ? 1 : 0; } @Override public Flux asFlux() { return this; } @Override protected boolean isIdentityProcessor() { return true; } void doTerminate() { Disposable r = onTerminate; if (r != null && ON_TERMINATE.compareAndSet(this, r, null)) { r.dispose(); } } void drainRegular(CoreSubscriber a) { int missed = 1; final Queue q = queue; for (;;) { long r = requested; long e = 0L; while (r != e) { boolean d = done; T t = q.poll(); boolean empty = t == null; if (checkTerminated(d, empty, a, q, t)) { return; } if (empty) { break; } a.onNext(t); e++; } if (r == e) { if (checkTerminated(done, q.isEmpty(), a, q, null)) { return; } } if (e != 0 && r != Long.MAX_VALUE) { REQUESTED.addAndGet(this, -e); } missed = WIP.addAndGet(this, -missed); if (missed == 0) { break; } } } void drainFused(CoreSubscriber a) { int missed = 1; for (;;) { if (cancelled) { // We are the holder of the queue, but we still have to perform discarding under the guarded block // to prevent any racing done by downstream this.clear(); hasDownstream = false; return; } boolean d = done; a.onNext(null); if (d) { hasDownstream = false; Throwable ex = error; if (ex != null) { a.onError(ex); } else { a.onComplete(); } return; } missed = WIP.addAndGet(this, -missed); if (missed == 0) { break; } } } void drain(@Nullable T dataSignalOfferedBeforeDrain) { if (WIP.getAndIncrement(this) != 0) { if (dataSignalOfferedBeforeDrain != null) { if (cancelled) { Operators.onDiscard(dataSignalOfferedBeforeDrain, actual.currentContext()); } else if (done) { Operators.onNextDropped(dataSignalOfferedBeforeDrain, currentContext()); } } return; } int missed = 1; for (;;) { CoreSubscriber a = actual; if (a != null) { if (outputFused) { drainFused(a); } else { drainRegular(a); } return; } missed = WIP.addAndGet(this, -missed); if (missed == 0) { break; } } } boolean checkTerminated(boolean d, boolean empty, CoreSubscriber a, Queue q, @Nullable T t) { if (cancelled) { Operators.onDiscard(t, a.currentContext()); Operators.onDiscardQueueWithClear(q, a.currentContext(), null); hasDownstream = false; return true; } if (d && empty) { Throwable e = error; hasDownstream = false; if (e != null) { a.onError(e); } else { a.onComplete(); } return true; } return false; } @Override public void onSubscribe(Subscription s) { if (done || cancelled) { s.cancel(); } else { s.request(Long.MAX_VALUE); } } @Override public int getPrefetch() { return Integer.MAX_VALUE; } @Override public Context currentContext() { CoreSubscriber actual = this.actual; return actual != null ? actual.currentContext() : Context.empty(); } @Override public void subscribe(CoreSubscriber actual) { Objects.requireNonNull(actual, "subscribe"); if (once == 0 && ONCE.compareAndSet(this, 0, 1)) { this.hasDownstream = true; actual.onSubscribe(this); this.actual = actual; if (cancelled) { this.hasDownstream = false; } else { drain(null); } } else { Operators.error(actual, new IllegalStateException("UnicastProcessor " + "allows only a single Subscriber")); } } @Override public void request(long n) { if (Operators.validate(n)) { Operators.addCap(REQUESTED, this, n); drain(null); } } @Override public void cancel() { if (cancelled) { return; } cancelled = true; doTerminate(); if (WIP.getAndIncrement(this) == 0) { if (!outputFused) { // discard MUST be happening only and only if there is no racing on elements consumption // which is guaranteed by the WIP guard here in case non-fused output Operators.onDiscardQueueWithClear(queue, currentContext(), null); } hasDownstream = false; } } @Override @Nullable public T poll() { return queue.poll(); } @Override public int size() { return queue.size(); } @Override public boolean isEmpty() { return queue.isEmpty(); } @Override public void clear() { // use guard on the queue instance as the best way to ensure there is no racing on draining // the call to this method must be done only during the ASYNC fusion so all the callers will be waiting // this should not be performance costly with the assumption the cancel is rare operation if (DISCARD_GUARD.getAndIncrement(this) != 0) { return; } int missed = 1; for (;;) { Operators.onDiscardQueueWithClear(queue, currentContext(), null); int dg = discardGuard; if (missed == dg) { missed = DISCARD_GUARD.addAndGet(this, -missed); if (missed == 0) { break; } } else { missed = dg; } } } @Override public int requestFusion(int requestedMode) { if ((requestedMode & Fuseable.ASYNC) != 0) { outputFused = true; return Fuseable.ASYNC; } return Fuseable.NONE; } @Override public boolean isDisposed() { return cancelled || done; } @Override public boolean isTerminated() { return done; } @Override @Nullable public Throwable getError() { return error; } @Override public CoreSubscriber actual() { return actual; } @Override public long downstreamCount() { return hasDownstreams() ? 1L : 0L; } @Override public boolean hasDownstreams() { return hasDownstream; } }




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