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Reactive Extensions for Java
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/**
 * Copyright (c) 2016-present, RxJava Contributors.
 *
 * 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 io.reactivex.internal.operators.parallel;

import java.util.concurrent.Callable;

import org.reactivestreams.*;

import io.reactivex.exceptions.Exceptions;
import io.reactivex.functions.BiConsumer;
import io.reactivex.internal.functions.ObjectHelper;
import io.reactivex.internal.subscribers.DeferredScalarSubscriber;
import io.reactivex.internal.subscriptions.*;
import io.reactivex.parallel.ParallelFlowable;
import io.reactivex.plugins.RxJavaPlugins;

/**
 * Reduce the sequence of values in each 'rail' to a single value.
 *
 * @param  the input value type
 * @param  the collection type
 */
public final class ParallelCollect extends ParallelFlowable {

    final ParallelFlowable source;

    final Callable initialCollection;

    final BiConsumer collector;

    public ParallelCollect(ParallelFlowable source,
            Callable initialCollection, BiConsumer collector) {
        this.source = source;
        this.initialCollection = initialCollection;
        this.collector = collector;
    }

    @Override
    public void subscribe(Subscriber[] subscribers) {
        if (!validate(subscribers)) {
            return;
        }

        int n = subscribers.length;
        @SuppressWarnings("unchecked")
        Subscriber[] parents = new Subscriber[n];

        for (int i = 0; i < n; i++) {

            C initialValue;

            try {
                initialValue = ObjectHelper.requireNonNull(initialCollection.call(), "The initialSupplier returned a null value");
            } catch (Throwable ex) {
                Exceptions.throwIfFatal(ex);
                reportError(subscribers, ex);
                return;
            }

            parents[i] = new ParallelCollectSubscriber(subscribers[i], initialValue, collector);
        }

        source.subscribe(parents);
    }

    void reportError(Subscriber[] subscribers, Throwable ex) {
        for (Subscriber s : subscribers) {
            EmptySubscription.error(ex, s);
        }
    }

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

    static final class ParallelCollectSubscriber extends DeferredScalarSubscriber {

        private static final long serialVersionUID = -4767392946044436228L;

        final BiConsumer collector;

        C collection;

        boolean done;

        ParallelCollectSubscriber(Subscriber subscriber,
                C initialValue, BiConsumer collector) {
            super(subscriber);
            this.collection = initialValue;
            this.collector = collector;
        }

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

                downstream.onSubscribe(this);

                s.request(Long.MAX_VALUE);
            }
        }

        @Override
        public void onNext(T t) {
            if (done) {
                return;
            }

            try {
                collector.accept(collection, t);
            } catch (Throwable ex) {
                Exceptions.throwIfFatal(ex);
                cancel();
                onError(ex);
            }
        }

        @Override
        public void onError(Throwable t) {
            if (done) {
                RxJavaPlugins.onError(t);
                return;
            }
            done = true;
            collection = null;
            downstream.onError(t);
        }

        @Override
        public void onComplete() {
            if (done) {
                return;
            }
            done = true;
            C c = collection;
            collection = null;
            complete(c);
        }

        @Override
        public void cancel() {
            super.cancel();
            upstream.cancel();
        }
    }
}