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 java.util.concurrent.atomic.*;
  
  import org.reactivestreams.*;
  
  import io.reactivex.rxjava3.core.*;
  import io.reactivex.rxjava3.core.Scheduler.Worker;
  import io.reactivex.rxjava3.exceptions.*;
  import io.reactivex.rxjava3.internal.schedulers.SchedulerMultiWorkerSupport;
  import io.reactivex.rxjava3.internal.schedulers.SchedulerMultiWorkerSupport.WorkerCallback;
  import io.reactivex.rxjava3.internal.subscriptions.SubscriptionHelper;
  import io.reactivex.rxjava3.internal.util.BackpressureHelper;
  import io.reactivex.rxjava3.operators.ConditionalSubscriber;
  import io.reactivex.rxjava3.operators.SpscArrayQueue;
  import io.reactivex.rxjava3.parallel.ParallelFlowable;
  import io.reactivex.rxjava3.plugins.RxJavaPlugins;
  
  /**
   * Ensures each 'rail' from upstream runs on a Worker from a Scheduler.
   *
   * @param <T> the value type
   */
  public final class ParallelRunOn<T> extends ParallelFlowable<T> {
      final ParallelFlowable<? extends T> source;
  
      final Scheduler scheduler;
  
      final int prefetch;
  
      public ParallelRunOn(ParallelFlowable<? extends T> parent,
              Scheduler scheduler, int prefetch) {
          this.source = parent;
          this.scheduler = scheduler;
          this.prefetch = prefetch;
      }
  
      @Override
      public void subscribe(Subscriber<? super T>[] subscribers) {
          subscribers = RxJavaPlugins.onSubscribe(this, subscribers);
  
          if (!validate(subscribers)) {
              return;
          }
  
          int n = subscribers.length;
  
          @SuppressWarnings("unchecked")
          final Subscriber<T>[] parents = new Subscriber[n];
  
          if (scheduler instanceof SchedulerMultiWorkerSupport) {
              SchedulerMultiWorkerSupport multiworker = (SchedulerMultiWorkerSupport) scheduler;
              multiworker.createWorkers(n, new MultiWorkerCallback(subscribers, parents));
          } else {
              for (int i = 0; i < n; i++) {
                  createSubscriber(i, subscribers, parents, scheduler.createWorker());
              }
          }
          source.subscribe(parents);
      }
  
      void createSubscriber(int i, Subscriber<? super T>[] subscribers,
              Subscriber<T>[] parents, Scheduler.Worker worker) {
  
          Subscriber<? super T> a = subscribers[i];
  
          SpscArrayQueue<T> q = new SpscArrayQueue<>(prefetch);
  
          if (a instanceof ConditionalSubscriber) {
              parents[i] = new RunOnConditionalSubscriber<>((ConditionalSubscriber<? super T>)a, prefetch, q, worker);
          } else {
              parents[i] = new RunOnSubscriber<>(a, prefetch, q, worker);
          }
      }
  
      final class MultiWorkerCallback implements WorkerCallback {
  
          final Subscriber<? super T>[] subscribers;
  
          final Subscriber<T>[] parents;
  
          MultiWorkerCallback(Subscriber<? super T>[] subscribers,
                  Subscriber<T>[] parents) {
              this.subscribers = subscribers;
              this.parents = parents;
          }
  
          @Override
          public void onWorker(int i, Worker w) {
              createSubscriber(i, subscribers, parents, w);
          }
      }
  
      @Override
      public int parallelism() {
          return source.parallelism();
      }
  
      abstract static class BaseRunOnSubscriber<T> extends AtomicInteger
      implements FlowableSubscriber<T>, Subscription, Runnable {
  
          private static final long serialVersionUID = 9222303586456402150L;
  
          final int prefetch;
  
          final int limit;
  
          final SpscArrayQueue<T> queue;
  
          final Worker worker;
  
          Subscription upstream;
  
          volatile boolean done;
  
          Throwable error;
  
          final AtomicLong requested = new AtomicLong();
  
          volatile boolean cancelled;
  
          int consumed;
  
          BaseRunOnSubscriber(int prefetch, SpscArrayQueue<T> queue, Worker worker) {
              this.prefetch = prefetch;
              this.queue = queue;
              this.limit = prefetch - (prefetch >> 2);
              this.worker = worker;
          }
  
          @Override
          public final void onNext(T t) {
              if (done) {
                  return;
              }
              if (!queue.offer(t)) {
                  upstream.cancel();
                  onError(new QueueOverflowException());
                  return;
              }
              schedule();
          }
  
          @Override
          public final void onError(Throwable t) {
              if (done) {
                  RxJavaPlugins.onError(t);
                  return;
              }
              error = t;
              done = true;
              schedule();
          }
  
          @Override
          public final void onComplete() {
              if (done) {
                  return;
              }
              done = true;
              schedule();
          }
  
          @Override
          public final void request(long n) {
              if (SubscriptionHelper.validate(n)) {
                  BackpressureHelper.add(requested, n);
                  schedule();
              }
          }
  
          @Override
          public final void cancel() {
              if (!cancelled) {
                  cancelled = true;
                  upstream.cancel();
                  worker.dispose();
  
                  if (getAndIncrement() == 0) {
                      queue.clear();
                  }
              }
          }
  
          final void schedule() {
              if (getAndIncrement() == 0) {
                  worker.schedule(this);
              }
          }
      }
  
      static final class RunOnSubscriber<T> extends BaseRunOnSubscriber<T> {
  
          private static final long serialVersionUID = 1075119423897941642L;
  
          final Subscriber<? super T> downstream;
  
          RunOnSubscriber(Subscriber<? super T> actual, int prefetch, SpscArrayQueue<T> queue, Worker worker) {
              super(prefetch, queue, worker);
              this.downstream = actual;
          }
  
          @Override
          public void onSubscribe(Subscription s) {
              if (SubscriptionHelper.validate(this.upstream, s)) {
                  this.upstream = s;
  
                  downstream.onSubscribe(this);
  
                  s.request(prefetch);
              }
          }
  
          @Override
          public void run() {
              int missed = 1;
              int c = consumed;
              SpscArrayQueue<T> q = queue;
              Subscriber<? super T> a = downstream;
              int lim = limit;
  
              for (;;) {
  
                  long r = requested.get();
                  long e = 0L;
  
                  while (e != r) {
                      if (cancelled) {
                          q.clear();
                          return;
                      }
  
                      boolean d = done;
  
                      if (d) {
                          Throwable ex = error;
                          if (ex != null) {
                              q.clear();
  
                              a.onError(ex);
  
                              worker.dispose();
                              return;
                          }
                      }
  
                      T v = q.poll();
  
                      boolean empty = v == null;
  
                      if (d && empty) {
                          a.onComplete();
  
                          worker.dispose();
                          return;
                      }
  
                      if (empty) {
                          break;
                      }
  
                      a.onNext(v);
  
                      e++;
  
                      int p = ++c;
                      if (p == lim) {
                          c = 0;
                          upstream.request(p);
                      }
                  }
  
                  if (e == r) {
                      if (cancelled) {
                          q.clear();
                          return;
                      }
  
                      if (done) {
                          Throwable ex = error;
                          if (ex != null) {
                              q.clear();
  
                              a.onError(ex);
  
                              worker.dispose();
                              return;
                          }
                          if (q.isEmpty()) {
                              a.onComplete();
  
                              worker.dispose();
                              return;
                          }
                      }
                  }
  
                  if (e != 0L && r != Long.MAX_VALUE) {
                      requested.addAndGet(-e);
                  }
  
                  int w = get();
                  if (w == missed) {
                      consumed = c;
                      missed = addAndGet(-missed);
                      if (missed == 0) {
                          break;
                      }
                  } else {
                      missed = w;
                  }
              }
          }
      }
  
      static final class RunOnConditionalSubscriber<T> extends BaseRunOnSubscriber<T> {
  
          private static final long serialVersionUID = 1075119423897941642L;
  
          final ConditionalSubscriber<? super T> downstream;
  
          RunOnConditionalSubscriber(ConditionalSubscriber<? super T> actual, int prefetch, SpscArrayQueue<T> queue, Worker worker) {
              super(prefetch, queue, worker);
              this.downstream = actual;
          }
  
          @Override
          public void onSubscribe(Subscription s) {
              if (SubscriptionHelper.validate(this.upstream, s)) {
                  this.upstream = s;
  
                  downstream.onSubscribe(this);
  
                  s.request(prefetch);
              }
          }
  
          @Override
          public void run() {
              int missed = 1;
              int c = consumed;
              SpscArrayQueue<T> q = queue;
              ConditionalSubscriber<? super T> a = downstream;
              int lim = limit;
  
              for (;;) {
  
                  long r = requested.get();
                  long e = 0L;
  
                  while (e != r) {
                      if (cancelled) {
                          q.clear();
                          return;
                      }
  
                      boolean d = done;
  
                      if (d) {
                          Throwable ex = error;
                          if (ex != null) {
                              q.clear();
  
                              a.onError(ex);
  
                              worker.dispose();
                              return;
                          }
                      }
  
                      T v = q.poll();
  
                      boolean empty = v == null;
  
                      if (d && empty) {
                          a.onComplete();
  
                          worker.dispose();
                          return;
                      }
  
                      if (empty) {
                          break;
                      }
  
                      if (a.tryOnNext(v)) {
                          e++;
                      }
  
                      int p = ++c;
                      if (p == lim) {
                          c = 0;
                          upstream.request(p);
                      }
                  }
  
                  if (e == r) {
                      if (cancelled) {
                          q.clear();
                          return;
                      }
  
                      if (done) {
                          Throwable ex = error;
                          if (ex != null) {
                              q.clear();
  
                              a.onError(ex);
  
                              worker.dispose();
                              return;
                          }
                          if (q.isEmpty()) {
                              a.onComplete();
  
                              worker.dispose();
                              return;
                          }
                      }
                  }
  
                  if (e != 0L) {
                      BackpressureHelper.produced(requested, e);
                  }
  
                  consumed = c;
                  missed = addAndGet(-missed);
                  if (missed == 0) {
                      break;
                  }
              }
          }
      }
  }
  