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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.concurrent.atomic.AtomicLongFieldUpdater;
import java.util.concurrent.atomic.AtomicReferenceFieldUpdater;
import java.util.stream.Stream;
import org.reactivestreams.Publisher;
import org.reactivestreams.Subscription;
import reactor.core.CorePublisher;
import reactor.core.CoreSubscriber;
import reactor.core.Exceptions;
import reactor.core.Scannable;
import reactor.util.annotation.Nullable;
import reactor.util.context.Context;
/**
* Samples the main source and emits its latest value whenever the other Publisher
* signals a value.
*
*
* Termination of either Publishers will result in termination for the Subscriber
* as well.
*
*
* Both Publishers will run in unbounded mode because the backpressure
* would interfere with the sampling precision.
*
* @param the input and output value type
* @param the value type of the sampler (irrelevant)
* @see Reactive-Streams-Commons
*/
final class FluxSample extends InternalFluxOperator {
final Publisher other;
FluxSample(Flux source, Publisher other) {
super(source);
this.other = Objects.requireNonNull(other, "other");
}
@Override
public int getPrefetch() {
return Integer.MAX_VALUE;
}
@Override
public CoreSubscriber subscribeOrReturn(CoreSubscriber actual) {
CoreSubscriber serial = Operators.serialize(actual);
SampleMainSubscriber main = new SampleMainSubscriber<>(serial);
actual.onSubscribe(main);
other.subscribe(new SampleOther<>(main));
return main;
}
@Override
public Object scanUnsafe(Attr key) {
if (key == Attr.RUN_STYLE) return Attr.RunStyle.SYNC;
return super.scanUnsafe(key);
}
static final class SampleMainSubscriber implements InnerOperator {
final CoreSubscriber actual;
final Context ctx;
volatile T value;
@SuppressWarnings("rawtypes")
static final AtomicReferenceFieldUpdater VALUE =
AtomicReferenceFieldUpdater.newUpdater(SampleMainSubscriber.class, Object.class, "value");
volatile Subscription main;
@SuppressWarnings("rawtypes")
static final AtomicReferenceFieldUpdater MAIN =
AtomicReferenceFieldUpdater.newUpdater(SampleMainSubscriber.class, Subscription.class, "main");
volatile Subscription other;
@SuppressWarnings("rawtypes")
static final AtomicReferenceFieldUpdater OTHER =
AtomicReferenceFieldUpdater.newUpdater(SampleMainSubscriber.class, Subscription.class, "other");
volatile long requested;
@SuppressWarnings("rawtypes")
static final AtomicLongFieldUpdater REQUESTED =
AtomicLongFieldUpdater.newUpdater(SampleMainSubscriber.class, "requested");
SampleMainSubscriber(CoreSubscriber actual) {
this.actual = actual;
this.ctx = actual.currentContext();
}
@Override
public final CoreSubscriber actual() {
return actual;
}
@Override
public Stream inners() {
return Stream.of(Scannable.from(other));
}
@Override
@Nullable
public Object scanUnsafe(Attr key) {
if (key == Attr.REQUESTED_FROM_DOWNSTREAM) return requested;
if (key == Attr.PARENT) return main;
if (key == Attr.CANCELLED) return main == Operators.cancelledSubscription();
if (key == Attr.BUFFERED) return value != null ? 1 : 0;
if (key == Attr.RUN_STYLE) return Attr.RunStyle.SYNC;
return InnerOperator.super.scanUnsafe(key);
}
@Override
public void onSubscribe(Subscription s) {
if (!MAIN.compareAndSet(this, null, s)) {
s.cancel();
if (main != Operators.cancelledSubscription()) {
Operators.reportSubscriptionSet();
}
return;
}
s.request(Long.MAX_VALUE);
}
void cancelMain() {
Subscription s = main;
if (s != Operators.cancelledSubscription()) {
s = MAIN.getAndSet(this, Operators.cancelledSubscription());
if (s != null && s != Operators.cancelledSubscription()) {
s.cancel();
}
}
}
void cancelOther() {
Subscription s = other;
if (s != Operators.cancelledSubscription()) {
s = OTHER.getAndSet(this, Operators.cancelledSubscription());
if (s != null && s != Operators.cancelledSubscription()) {
s.cancel();
}
}
}
void setOther(Subscription s) {
if (!OTHER.compareAndSet(this, null, s)) {
s.cancel();
if (other != Operators.cancelledSubscription()) {
Operators.reportSubscriptionSet();
}
return;
}
s.request(Long.MAX_VALUE);
}
@Override
public void request(long n) {
if (Operators.validate(n)) {
Operators.addCap(REQUESTED, this, n);
}
}
@Override
public void cancel() {
cancelMain();
cancelOther();
}
@Override
public void onNext(T t) {
Object old = VALUE.getAndSet(this, t);
if (old != null) {
Operators.onDiscard(old, ctx);
}
}
@Override
public void onError(Throwable t) {
cancelOther();
actual.onError(t);
}
@Override
public void onComplete() {
cancelOther();
//implementation note: if the sampler triggers at the exact same time as the
// last source value being emitted, it could be that the sampler "wins" and
// suppresses the value by cancelling the main. In any other case, the block
// below ensures last source value is always part of the sample.
T v = value;
if (v != null) {
actual.onNext(value);
}
actual.onComplete();
}
@SuppressWarnings("unchecked")
@Nullable
T getAndNullValue() {
return (T) VALUE.getAndSet(this, null);
}
void decrement() {
REQUESTED.decrementAndGet(this);
}
}
static final class SampleOther implements InnerConsumer {
final SampleMainSubscriber main;
SampleOther(SampleMainSubscriber main) {
this.main = main;
}
@Override
@Nullable
public Object scanUnsafe(Attr key) {
if (key == Attr.PARENT) return main.other;
if (key == Attr.ACTUAL) return main;
if (key == Attr.CANCELLED) return main.other == Operators.cancelledSubscription();
if (key == Attr.PREFETCH) return Integer.MAX_VALUE;
if (key == Attr.RUN_STYLE) return Attr.RunStyle.SYNC;
return null;
}
@Override
public Context currentContext() {
return main.currentContext();
}
@Override
public void onSubscribe(Subscription s) {
main.setOther(s);
}
@Override
public void onNext(U t) {
SampleMainSubscriber m = main;
T v = m.getAndNullValue();
if (v != null) {
if (m.requested != 0L) {
m.actual.onNext(v);
if (m.requested != Long.MAX_VALUE) {
m.decrement();
}
return;
}
m.cancel();
m.actual.onError(Exceptions.failWithOverflow("Can't signal value due to lack of requests"));
Operators.onDiscard(v, m.ctx);
}
}
@Override
public void onError(Throwable t) {
SampleMainSubscriber m = main;
m.cancelMain();
m.actual.onError(t);
}
@Override
public void onComplete() {
SampleMainSubscriber m = main;
m.cancelMain();
m.actual.onComplete();
}
}
}