/*
 * 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.util.Objects;
import java.util.function.BiFunction;
import java.util.function.Supplier;

import org.reactivestreams.Subscriber;
import org.reactivestreams.Subscription;
import reactor.core.CoreSubscriber;
import reactor.core.Fuseable;
import reactor.core.Scannable;
import reactor.util.annotation.Nullable;

Reduce the sequence of values in each 'rail' to a single value.
Type parameters:
  • <T> – the input value type
  • <R> – the result value type
/** * Reduce the sequence of values in each 'rail' to a single value. * * @param <T> the input value type * @param <R> the result value type */
final class ParallelReduceSeed<T, R> extends ParallelFlux<R> implements Scannable, Fuseable { final ParallelFlux<? extends T> source; final Supplier<R> initialSupplier; final BiFunction<R, ? super T, R> reducer; ParallelReduceSeed(ParallelFlux<? extends T> source, Supplier<R> initialSupplier, BiFunction<R, ? super T, R> reducer) { this.source = source; this.initialSupplier = initialSupplier; this.reducer = reducer; } @Override @Nullable public Object scanUnsafe(Scannable.Attr key) { if (key == Attr.PARENT) return source; if (key == Attr.PREFETCH) return getPrefetch(); return null; } @Override public int getPrefetch() { return Integer.MAX_VALUE; } @Override public void subscribe(CoreSubscriber<? super R>[] subscribers) { if (!validate(subscribers)) { return; } int n = subscribers.length; @SuppressWarnings("unchecked") CoreSubscriber<T>[] parents = new CoreSubscriber[n]; for (int i = 0; i < n; i++) { R initialValue; try { initialValue = Objects.requireNonNull(initialSupplier.get(), "The initialSupplier returned a null value"); } catch (Throwable ex) { reportError(subscribers, Operators.onOperatorError(ex, subscribers[i].currentContext())); return; } parents[i] = new ParallelReduceSeedSubscriber<>(subscribers[i], initialValue, reducer); } source.subscribe(parents); } void reportError(Subscriber<?>[] subscribers, Throwable ex) { for (Subscriber<?> s : subscribers) { Operators.error(s, ex); } } @Override public int parallelism() { return source.parallelism(); } static final class ParallelReduceSeedSubscriber<T, R> extends Operators.MonoSubscriber<T, R> { final BiFunction<R, ? super T, R> reducer; R accumulator; Subscription s; boolean done; ParallelReduceSeedSubscriber(CoreSubscriber<? super R> subscriber, R initialValue, BiFunction<R, ? super T, R> reducer) { super(subscriber); this.accumulator = initialValue; this.reducer = reducer; } @Override public void onSubscribe(Subscription s) { if (Operators.validate(this.s, s)) { this.s = s; actual.onSubscribe(this); s.request(Long.MAX_VALUE); } } @Override public void onNext(T t) { if (done) { Operators.onNextDropped(t, actual.currentContext()); return; } R v; try { v = Objects.requireNonNull(reducer.apply(accumulator, t), "The reducer returned a null value"); } catch (Throwable ex) { onError(Operators.onOperatorError(this, ex, t, actual.currentContext())); return; } accumulator = v; } @Override public void onError(Throwable t) { if (done) { Operators.onErrorDropped(t, actual.currentContext()); return; } done = true; accumulator = null; actual.onError(t); } @Override public void onComplete() { if (done) { return; } done = true; R a = accumulator; accumulator = null; complete(a); } @Override public void cancel() { super.cancel(); s.cancel(); } } }