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/*
* Copyright (c) 2016-2023 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.time.Duration;
import java.util.Objects;
import java.util.concurrent.Callable;
import java.util.concurrent.atomic.AtomicIntegerFieldUpdater;
import reactor.core.CoreSubscriber;
import reactor.core.Exceptions;
import reactor.core.Fuseable;
import reactor.util.annotation.Nullable;
/**
* Executes a Callable function and emits a single value to each individual Subscriber.
*
* Preferred to {@link java.util.function.Supplier} because the Callable may throw.
*
* @param the returned value type
* @see Reactive-Streams-Commons
*/
final class MonoCallable extends Mono
implements Callable, Fuseable, SourceProducer {
final Callable extends T> callable;
MonoCallable(Callable extends T> callable) {
this.callable = Objects.requireNonNull(callable, "callable");
}
@Override
public void subscribe(CoreSubscriber super T> actual) {
actual.onSubscribe(new MonoCallableSubscription<>(actual, this.callable));
}
@Override
@Nullable
public T block() {
//duration is ignored below
return block(Duration.ZERO);
}
@Override
@Nullable
public T block(Duration m) {
try {
return callable.call();
}
catch (Throwable e) {
throw Exceptions.propagate(e);
}
}
@Override
@Nullable
public T call() throws Exception {
return callable.call();
}
@Override
public Object scanUnsafe(Attr key) {
if (key == Attr.RUN_STYLE) return Attr.RunStyle.SYNC;
return SourceProducer.super.scanUnsafe(key);
}
static class MonoCallableSubscription
implements InnerProducer, Fuseable, QueueSubscription {
final CoreSubscriber super T> actual;
final Callable extends T> callable;
boolean done;
volatile int requestedOnce;
@SuppressWarnings("rawtypes")
static final AtomicIntegerFieldUpdater REQUESTED_ONCE =
AtomicIntegerFieldUpdater.newUpdater(MonoCallableSubscription.class,
"requestedOnce");
volatile boolean cancelled;
MonoCallableSubscription(CoreSubscriber super T> actual, Callable extends T> callable) {
this.actual = actual;
this.callable = callable;
}
@Override
public CoreSubscriber super T> actual() {
return this.actual;
}
@Override
public T poll() {
if (this.done) {
return null;
}
this.done = true;
try {
return this.callable.call();
}
catch (Throwable e) {
throw Exceptions.propagate(e);
}
}
@Override
public void request(long n) {
if (this.cancelled) {
return;
}
if (this.requestedOnce == 1 || !REQUESTED_ONCE.compareAndSet(this, 0 , 1)) {
return;
}
final CoreSubscriber super T> s = this.actual;
final T value;
try {
value = this.callable.call();
}
catch (Exception e) {
if (this.cancelled) {
Operators.onErrorDropped(e, s.currentContext());
return;
}
s.onError(e);
return;
}
if (this.cancelled) {
Operators.onDiscard(value, s.currentContext());
return;
}
if (value != null) {
s.onNext(value);
}
s.onComplete();
}
@Override
public void cancel() {
this.cancelled = true;
}
@Override
public int requestFusion(int requestedMode) {
return requestedMode & SYNC;
}
@Override
public int size() {
return this.done ? 0 : 1;
}
@Override
public boolean isEmpty() {
return this.done;
}
@Override
public void clear() {
this.done = true;
}
}
}