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.schedulers;
  
  import java.util.concurrent.*;
  import java.util.concurrent.atomic.AtomicReference;
  
  import io.reactivex.rxjava3.annotations.NonNull;
  import io.reactivex.rxjava3.core.Scheduler;
  import io.reactivex.rxjava3.disposables.*;
  import io.reactivex.rxjava3.internal.disposables.*;
  import io.reactivex.rxjava3.internal.functions.ObjectHelper;
  
  /**
   * Holds a fixed pool of worker threads and assigns them
   * to requested Scheduler.Workers in a round-robin fashion.
   */
  public final class ComputationScheduler extends Scheduler implements SchedulerMultiWorkerSupport {
      /** This will indicate no pool is active. */
      static final FixedSchedulerPool NONE;
      /** Manages a fixed number of workers. */
      private static final String THREAD_NAME_PREFIX = "RxComputationThreadPool";
      static final RxThreadFactory THREAD_FACTORY;
      /**
       * Key to setting the maximum number of computation scheduler threads.
       * Zero or less is interpreted as use available. Capped by available.
       */
      static final String KEY_MAX_THREADS = "rx3.computation-threads";
      /** The maximum number of computation scheduler threads. */
      static final int MAX_THREADS;
  
      static final PoolWorker SHUTDOWN_WORKER;
  
      final ThreadFactory threadFactory;
      final AtomicReference<FixedSchedulerPool> pool;
      /** The name of the system property for setting the thread priority for this Scheduler. */
      private static final String KEY_COMPUTATION_PRIORITY = "rx3.computation-priority";
  
      static {
          MAX_THREADS = cap(Runtime.getRuntime().availableProcessors(), Integer.getInteger(KEY_MAX_THREADS, 0));
  
          SHUTDOWN_WORKER = new PoolWorker(new RxThreadFactory("RxComputationShutdown"));
          SHUTDOWN_WORKER.dispose();
  
          int priority = Math.max(Thread.MIN_PRIORITY, Math.min(Thread.MAX_PRIORITY,
                  Integer.getInteger(KEY_COMPUTATION_PRIORITY, Thread.NORM_PRIORITY)));
  
          THREAD_FACTORY = new RxThreadFactory(THREAD_NAME_PREFIX, priority, true);
  
          NONE = new FixedSchedulerPool(0, THREAD_FACTORY);
          NONE.shutdown();
      }
  
      static int cap(int cpuCount, int paramThreads) {
          return paramThreads <= 0 || paramThreads > cpuCount ? cpuCount : paramThreads;
      }
  
      static final class FixedSchedulerPool implements SchedulerMultiWorkerSupport {
          final int cores;
  
          final PoolWorker[] eventLoops;
          long n;
  
          FixedSchedulerPool(int maxThreads, ThreadFactory threadFactory) {
              // initialize event loops
              this.cores = maxThreads;
              this.eventLoops = new PoolWorker[maxThreads];
              for (int i = 0; i < maxThreads; i++) {
                  this.eventLoops[i] = new PoolWorker(threadFactory);
              }
          }
  
          public PoolWorker getEventLoop() {
              int c = cores;
              if (c == 0) {
                  return SHUTDOWN_WORKER;
              }
              // simple round robin, improvements to come
              return eventLoops[(int)(n++ % c)];
          }
  
          public void shutdown() {
              for (PoolWorker w : eventLoops) {
                  w.dispose();
              }
          }
  
          @Override
          public void createWorkers(int number, WorkerCallback callback) {
              int c = cores;
              if (c == 0) {
                  for (int i = 0; i < number; i++) {
                      callback.onWorker(i, SHUTDOWN_WORKER);
                  }
              } else {
                  int index = (int)n % c;
                  for (int i = 0; i < number; i++) {
                      callback.onWorker(i, new EventLoopWorker(eventLoops[index]));
                      if (++index == c) {
                          index = 0;
                      }
                  }
                  n = index;
              }
          }
      }
  
      /**
       * Create a scheduler with pool size equal to the available processor
       * count and using least-recent worker selection policy.
       */
      public ComputationScheduler() {
          this(THREAD_FACTORY);
      }
  
      /**
       * Create a scheduler with pool size equal to the available processor
       * count and using least-recent worker selection policy.
       *
       * @param threadFactory thread factory to use for creating worker threads. Note that this takes precedence over any
       *                      system properties for configuring new thread creation. Cannot be null.
       */
      public ComputationScheduler(ThreadFactory threadFactory) {
          this.threadFactory = threadFactory;
          this.pool = new AtomicReference<>(NONE);
          start();
      }
  
      @NonNull
      @Override
      public Worker createWorker() {
          return new EventLoopWorker(pool.get().getEventLoop());
      }
  
      @Override
      public void createWorkers(int number, WorkerCallback callback) {
          ObjectHelper.verifyPositive(number, "number > 0 required");
          pool.get().createWorkers(number, callback);
      }
  
      @NonNull
      @Override
      public Disposable scheduleDirect(@NonNull Runnable run, long delay, TimeUnit unit) {
          PoolWorker w = pool.get().getEventLoop();
          return w.scheduleDirect(run, delay, unit);
      }
  
      @NonNull
      @Override
      public Disposable schedulePeriodicallyDirect(@NonNull Runnable run, long initialDelay, long period, TimeUnit unit) {
          PoolWorker w = pool.get().getEventLoop();
          return w.schedulePeriodicallyDirect(run, initialDelay, period, unit);
      }
  
      @Override
      public void start() {
          FixedSchedulerPool update = new FixedSchedulerPool(MAX_THREADS, threadFactory);
          if (!pool.compareAndSet(NONE, update)) {
              update.shutdown();
          }
      }
  
      @Override
      public void shutdown() {
          FixedSchedulerPool curr = pool.getAndSet(NONE);
          if (curr != NONE) {
              curr.shutdown();
          }
      }
  
      static final class EventLoopWorker extends Scheduler.Worker {
          private final ListCompositeDisposable serial;
          private final CompositeDisposable timed;
          private final ListCompositeDisposable both;
          private final PoolWorker poolWorker;
  
          volatile boolean disposed;
  
          EventLoopWorker(PoolWorker poolWorker) {
              this.poolWorker = poolWorker;
              this.serial = new ListCompositeDisposable();
              this.timed = new CompositeDisposable();
              this.both = new ListCompositeDisposable();
              this.both.add(serial);
              this.both.add(timed);
          }
  
          @Override
          public void dispose() {
              if (!disposed) {
                  disposed = true;
                  both.dispose();
              }
          }
  
          @Override
          public boolean isDisposed() {
              return disposed;
          }
  
          @NonNull
          @Override
          public Disposable schedule(@NonNull Runnable action) {
              if (disposed) {
                  return EmptyDisposable.INSTANCE;
              }
  
              return poolWorker.scheduleActual(action, 0, TimeUnit.MILLISECONDS, serial);
          }
  
          @NonNull
          @Override
          public Disposable schedule(@NonNull Runnable action, long delayTime, @NonNull TimeUnit unit) {
              if (disposed) {
                  return EmptyDisposable.INSTANCE;
              }
  
              return poolWorker.scheduleActual(action, delayTime, unit, timed);
          }
      }
  
      static final class PoolWorker extends NewThreadWorker {
          PoolWorker(ThreadFactory threadFactory) {
              super(threadFactory);
          }
      }
  }
  