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Reactive Extensions for Java
There is a newer version: 3.1.9
/*
 * 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.rxjava3.internal.operators.parallel;

import org.reactivestreams.*;

import io.reactivex.rxjava3.core.FlowableSubscriber;
import io.reactivex.rxjava3.exceptions.Exceptions;
import io.reactivex.rxjava3.functions.Function;
import io.reactivex.rxjava3.internal.subscriptions.SubscriptionHelper;
import io.reactivex.rxjava3.operators.ConditionalSubscriber;
import io.reactivex.rxjava3.parallel.ParallelFlowable;
import io.reactivex.rxjava3.plugins.RxJavaPlugins;

import java.util.Objects;

/**
 * Maps each 'rail' of the source ParallelFlowable with a mapper function.
 *
 * @param  the input value type
 * @param  the output value type
 */
public final class ParallelMap extends ParallelFlowable {

    final ParallelFlowable source;

    final Function mapper;

    public ParallelMap(ParallelFlowable source, Function mapper) {
        this.source = source;
        this.mapper = mapper;
    }

    @Override
    public void subscribe(Subscriber[] subscribers) {
        subscribers = RxJavaPlugins.onSubscribe(this, subscribers);

        if (!validate(subscribers)) {
            return;
        }

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

        for (int i = 0; i < n; i++) {
            Subscriber a = subscribers[i];
            if (a instanceof ConditionalSubscriber) {
                parents[i] = new ParallelMapConditionalSubscriber((ConditionalSubscriber)a, mapper);
            } else {
                parents[i] = new ParallelMapSubscriber(a, mapper);
            }
        }

        source.subscribe(parents);
    }

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

    static final class ParallelMapSubscriber implements FlowableSubscriber, Subscription {

        final Subscriber downstream;

        final Function mapper;

        Subscription upstream;

        boolean done;

        ParallelMapSubscriber(Subscriber actual, Function mapper) {
            this.downstream = actual;
            this.mapper = mapper;
        }

        @Override
        public void request(long n) {
            upstream.request(n);
        }

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

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

                downstream.onSubscribe(this);
            }
        }

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

            try {
                v = Objects.requireNonNull(mapper.apply(t), "The mapper returned a null value");
            } catch (Throwable ex) {
                Exceptions.throwIfFatal(ex);
                cancel();
                onError(ex);
                return;
            }

            downstream.onNext(v);
        }

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

        @Override
        public void onComplete() {
            if (done) {
                return;
            }
            done = true;
            downstream.onComplete();
        }

    }
    static final class ParallelMapConditionalSubscriber implements ConditionalSubscriber, Subscription {

        final ConditionalSubscriber downstream;

        final Function mapper;

        Subscription upstream;

        boolean done;

        ParallelMapConditionalSubscriber(ConditionalSubscriber actual, Function mapper) {
            this.downstream = actual;
            this.mapper = mapper;
        }

        @Override
        public void request(long n) {
            upstream.request(n);
        }

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

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

                downstream.onSubscribe(this);
            }
        }

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

            try {
                v = Objects.requireNonNull(mapper.apply(t), "The mapper returned a null value");
            } catch (Throwable ex) {
                Exceptions.throwIfFatal(ex);
                cancel();
                onError(ex);
                return;
            }

            downstream.onNext(v);
        }

        @Override
        public boolean tryOnNext(T t) {
            if (done) {
                return false;
            }
            R v;

            try {
                v = Objects.requireNonNull(mapper.apply(t), "The mapper returned a null value");
            } catch (Throwable ex) {
                Exceptions.throwIfFatal(ex);
                cancel();
                onError(ex);
                return false;
            }

            return downstream.tryOnNext(v);
        }

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

        @Override
        public void onComplete() {
            if (done) {
                return;
            }
            done = true;
            downstream.onComplete();
        }

    }
}