code: /*
   * 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.exceptions.Exceptions;
  import io.reactivex.rxjava3.functions.*;
  import io.reactivex.rxjava3.internal.subscribers.DeferredScalarSubscriber;
  import io.reactivex.rxjava3.internal.subscriptions.*;
  import io.reactivex.rxjava3.parallel.ParallelFlowable;
  import io.reactivex.rxjava3.plugins.RxJavaPlugins;
  
  import java.util.Objects;
  
  /**
   * Reduce the sequence of values in each 'rail' to a single value.
   *
   * @param <T> the input value type
   * @param <C> the collection type
   */
  public final class ParallelCollect<T, C> extends ParallelFlowable<C> {
  
      final ParallelFlowable<? extends T> source;
  
      final Supplier<? extends C> initialCollection;
  
      final BiConsumer<? super C, ? super T> collector;
  
      public ParallelCollect(ParallelFlowable<? extends T> source,
              Supplier<? extends C> initialCollection, BiConsumer<? super C, ? super T> collector) {
          this.source = source;
          this.initialCollection = initialCollection;
          this.collector = collector;
      }
  
      @Override
      public void subscribe(Subscriber<? super C>[] subscribers) {
          subscribers = RxJavaPlugins.onSubscribe(this, subscribers);
  
          if (!validate(subscribers)) {
              return;
          }
  
          int n = subscribers.length;
          @SuppressWarnings("unchecked")
          Subscriber<T>[] parents = new Subscriber[n];
  
          for (int i = 0; i < n; i++) {
  
              C initialValue;
  
              try {
                  initialValue = Objects.requireNonNull(initialCollection.get(), "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<T, C> extends DeferredScalarSubscriber<T, C> {
  
          private static final long serialVersionUID = -4767392946044436228L;
  
          final BiConsumer<? super C, ? super T> collector;
  
          C collection;
  
          boolean done;
  
          ParallelCollectSubscriber(Subscriber<? super C> subscriber,
                  C initialValue, BiConsumer<? super C, ? super T> 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();
          }
      }
  }
  