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.AtomicInteger;
  
  import io.reactivex.rxjava3.annotations.NonNull;
  import io.reactivex.rxjava3.core.Scheduler;
  import io.reactivex.rxjava3.disposables.*;
  import io.reactivex.rxjava3.internal.disposables.EmptyDisposable;
  import io.reactivex.rxjava3.plugins.RxJavaPlugins;
  
  /**
   * Schedules work on the current thread but does not execute immediately. Work is put in a queue and executed
   * after the current unit of work is completed.
   */
  public final class TrampolineScheduler extends Scheduler {
      private static final TrampolineScheduler INSTANCE = new TrampolineScheduler();
  
      public static TrampolineScheduler instance() {
          return INSTANCE;
      }
  
      @NonNull
      @Override
      public Worker createWorker() {
          return new TrampolineWorker();
      }
  
      /* package accessible for unit tests */TrampolineScheduler() {
      }
  
      @NonNull
      @Override
      public Disposable scheduleDirect(@NonNull Runnable run) {
          RxJavaPlugins.onSchedule(run).run();
          return EmptyDisposable.INSTANCE;
      }
  
      @NonNull
      @Override
      public Disposable scheduleDirect(@NonNull Runnable run, long delay, TimeUnit unit) {
          try {
              unit.sleep(delay);
              RxJavaPlugins.onSchedule(run).run();
          } catch (InterruptedException ex) {
              Thread.currentThread().interrupt();
              RxJavaPlugins.onError(ex);
          }
          return EmptyDisposable.INSTANCE;
      }
  
      static final class TrampolineWorker extends Scheduler.Worker {
          final PriorityBlockingQueue<TimedRunnable> queue = new PriorityBlockingQueue<>();
  
          private final AtomicInteger wip = new AtomicInteger();
  
          final AtomicInteger counter = new AtomicInteger();
  
          volatile boolean disposed;
  
          @NonNull
          @Override
          public Disposable schedule(@NonNull Runnable action) {
              return enqueue(action, now(TimeUnit.MILLISECONDS));
          }
  
          @NonNull
          @Override
          public Disposable schedule(@NonNull Runnable action, long delayTime, @NonNull TimeUnit unit) {
              long execTime = now(TimeUnit.MILLISECONDS) + unit.toMillis(delayTime);
  
              return enqueue(new SleepingRunnable(action, this, execTime), execTime);
          }
  
          Disposable enqueue(Runnable action, long execTime) {
              if (disposed) {
                  return EmptyDisposable.INSTANCE;
              }
              final TimedRunnable timedRunnable = new TimedRunnable(action, execTime, counter.incrementAndGet());
              queue.add(timedRunnable);
  
              if (wip.getAndIncrement() == 0) {
                  int missed = 1;
                  for (;;) {
                      for (;;) {
                          if (disposed) {
                              queue.clear();
                              return EmptyDisposable.INSTANCE;
                          }
                          final TimedRunnable polled = queue.poll();
                          if (polled == null) {
                              break;
                          }
                          if (!polled.disposed) {
                              polled.run.run();
                          }
                      }
                      missed = wip.addAndGet(-missed);
                      if (missed == 0) {
                          break;
                      }
                  }
  
                  return EmptyDisposable.INSTANCE;
              } else {
                  // queue wasn't empty, a parent is already processing so we just add to the end of the queue
                  return Disposable.fromRunnable(new AppendToQueueTask(timedRunnable));
              }
          }
  
          @Override
          public void dispose() {
              disposed = true;
          }
  
          @Override
          public boolean isDisposed() {
              return disposed;
          }
  
          final class AppendToQueueTask implements Runnable {
              final TimedRunnable timedRunnable;
  
              AppendToQueueTask(TimedRunnable timedRunnable) {
                  this.timedRunnable = timedRunnable;
              }
  
              @Override
              public void run() {
                  timedRunnable.disposed = true;
                  queue.remove(timedRunnable);
              }
          }
      }
  
      static final class TimedRunnable implements Comparable<TimedRunnable> {
          final Runnable run;
          final long execTime;
          final int count; // In case if time between enqueueing took less than 1ms
  
          volatile boolean disposed;
  
          TimedRunnable(Runnable run, Long execTime, int count) {
              this.run = run;
              this.execTime = execTime;
              this.count = count;
          }
  
          @Override
          public int compareTo(TimedRunnable that) {
              int result = Long.compare(execTime, that.execTime);
              if (result == 0) {
                  return Integer.compare(count, that.count);
              }
              return result;
          }
      }
  
      static final class SleepingRunnable implements Runnable {
          private final Runnable run;
          private final TrampolineWorker worker;
          private final long execTime;
  
          SleepingRunnable(Runnable run, TrampolineWorker worker, long execTime) {
              this.run = run;
              this.worker = worker;
              this.execTime = execTime;
          }
  
          @Override
          public void run() {
              if (!worker.disposed) {
                  long t = worker.now(TimeUnit.MILLISECONDS);
                  if (execTime > t) {
                      long delay = execTime - t;
                      try {
                          Thread.sleep(delay);
                      } catch (InterruptedException e) {
                          Thread.currentThread().interrupt();
                          RxJavaPlugins.onError(e);
                          return;
                      }
                  }
  
                  if (!worker.disposed) {
                      run.run();
                  }
              }
          }
      }
  }
  