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.observable;
  
  import io.reactivex.rxjava3.annotations.Nullable;
  import io.reactivex.rxjava3.core.*;
  import io.reactivex.rxjava3.disposables.Disposable;
  import io.reactivex.rxjava3.exceptions.Exceptions;
  import io.reactivex.rxjava3.internal.disposables.DisposableHelper;
  import io.reactivex.rxjava3.internal.observers.BasicIntQueueDisposable;
  import io.reactivex.rxjava3.internal.schedulers.TrampolineScheduler;
  import io.reactivex.rxjava3.operators.QueueDisposable;
  import io.reactivex.rxjava3.operators.SimpleQueue;
  import io.reactivex.rxjava3.operators.SpscLinkedArrayQueue;
  import io.reactivex.rxjava3.plugins.RxJavaPlugins;
  
  public final class ObservableObserveOn<T> extends AbstractObservableWithUpstream<T, T> {
      final Scheduler scheduler;
      final boolean delayError;
      final int bufferSize;
      public ObservableObserveOn(ObservableSource<T> source, Scheduler scheduler, boolean delayError, int bufferSize) {
          super(source);
          this.scheduler = scheduler;
          this.delayError = delayError;
          this.bufferSize = bufferSize;
      }
  
      @Override
      protected void subscribeActual(Observer<? super T> observer) {
          if (scheduler instanceof TrampolineScheduler) {
              source.subscribe(observer);
          } else {
              Scheduler.Worker w = scheduler.createWorker();
  
              source.subscribe(new ObserveOnObserver<>(observer, w, delayError, bufferSize));
          }
      }
  
      static final class ObserveOnObserver<T> extends BasicIntQueueDisposable<T>
      implements Observer<T>, Runnable {
  
          private static final long serialVersionUID = 6576896619930983584L;
          final Observer<? super T> downstream;
          final Scheduler.Worker worker;
          final boolean delayError;
          final int bufferSize;
  
          SimpleQueue<T> queue;
  
          Disposable upstream;
  
          Throwable error;
          volatile boolean done;
  
          volatile boolean disposed;
  
          int sourceMode;
  
          boolean outputFused;
  
          ObserveOnObserver(Observer<? super T> actual, Scheduler.Worker worker, boolean delayError, int bufferSize) {
              this.downstream = actual;
              this.worker = worker;
              this.delayError = delayError;
              this.bufferSize = bufferSize;
          }
  
          @Override
          public void onSubscribe(Disposable d) {
              if (DisposableHelper.validate(this.upstream, d)) {
                  this.upstream = d;
                  if (d instanceof QueueDisposable) {
                      @SuppressWarnings("unchecked")
                      QueueDisposable<T> qd = (QueueDisposable<T>) d;
  
                      int m = qd.requestFusion(QueueDisposable.ANY | QueueDisposable.BOUNDARY);
  
                      if (m == QueueDisposable.SYNC) {
                          sourceMode = m;
                          queue = qd;
                          done = true;
                          downstream.onSubscribe(this);
                          schedule();
                          return;
                      }
                      if (m == QueueDisposable.ASYNC) {
                          sourceMode = m;
                          queue = qd;
                          downstream.onSubscribe(this);
                          return;
                      }
                  }
  
                  queue = new SpscLinkedArrayQueue<>(bufferSize);
  
                  downstream.onSubscribe(this);
              }
          }
  
          @Override
          public void onNext(T t) {
              if (done) {
                  return;
              }
  
              if (sourceMode != QueueDisposable.ASYNC) {
                  queue.offer(t);
              }
              schedule();
          }
  
          @Override
          public void onError(Throwable t) {
              if (done) {
                  RxJavaPlugins.onError(t);
                  return;
              }
              error = t;
              done = true;
              schedule();
          }
  
          @Override
          public void onComplete() {
              if (done) {
                  return;
              }
              done = true;
              schedule();
          }
  
          @Override
          public void dispose() {
              if (!disposed) {
                  disposed = true;
                  upstream.dispose();
                  worker.dispose();
                  if (!outputFused && getAndIncrement() == 0) {
                      queue.clear();
                  }
              }
          }
  
          @Override
          public boolean isDisposed() {
              return disposed;
          }
  
          void schedule() {
              if (getAndIncrement() == 0) {
                  worker.schedule(this);
              }
          }
  
          void drainNormal() {
              int missed = 1;
  
              final SimpleQueue<T> q = queue;
              final Observer<? super T> a = downstream;
  
              for (;;) {
                  if (checkTerminated(done, q.isEmpty(), a)) {
                      return;
                  }
  
                  for (;;) {
                      boolean d = done;
                      T v;
  
                      try {
                          v = q.poll();
                      } catch (Throwable ex) {
                          Exceptions.throwIfFatal(ex);
                          disposed = true;
                          upstream.dispose();
                          q.clear();
                          a.onError(ex);
                          worker.dispose();
                          return;
                      }
                      boolean empty = v == null;
  
                      if (checkTerminated(d, empty, a)) {
                          return;
                      }
  
                      if (empty) {
                          break;
                      }
  
                      a.onNext(v);
                  }
  
                  missed = addAndGet(-missed);
                  if (missed == 0) {
                      break;
                  }
              }
          }
  
          void drainFused() {
              int missed = 1;
  
              for (;;) {
                  if (disposed) {
                      return;
                  }
  
                  boolean d = done;
                  Throwable ex = error;
  
                  if (!delayError && d && ex != null) {
                      disposed = true;
                      downstream.onError(error);
                      worker.dispose();
                      return;
                  }
  
                  downstream.onNext(null);
  
                  if (d) {
                      disposed = true;
                      ex = error;
                      if (ex != null) {
                          downstream.onError(ex);
                      } else {
                          downstream.onComplete();
                      }
                      worker.dispose();
                      return;
                  }
  
                  missed = addAndGet(-missed);
                  if (missed == 0) {
                      break;
                  }
              }
          }
  
          @Override
          public void run() {
              if (outputFused) {
                  drainFused();
              } else {
                  drainNormal();
              }
          }
  
          boolean checkTerminated(boolean d, boolean empty, Observer<? super T> a) {
              if (disposed) {
                  queue.clear();
                  return true;
              }
              if (d) {
                  Throwable e = error;
                  if (delayError) {
                      if (empty) {
                          disposed = true;
                          if (e != null) {
                              a.onError(e);
                          } else {
                              a.onComplete();
                          }
                          worker.dispose();
                          return true;
                      }
                  } else {
                      if (e != null) {
                          disposed = true;
                          queue.clear();
                          a.onError(e);
                          worker.dispose();
                          return true;
                      } else
                      if (empty) {
                          disposed = true;
                          a.onComplete();
                          worker.dispose();
                          return true;
                      }
                  }
              }
              return false;
          }
  
          @Override
          public int requestFusion(int mode) {
              if ((mode & ASYNC) != 0) {
                  outputFused = true;
                  return ASYNC;
              }
              return NONE;
          }
  
          @Nullable
          @Override
          public T poll() throws Throwable {
              return queue.poll();
          }
  
          @Override
          public void clear() {
              queue.clear();
          }
  
          @Override
          public boolean isEmpty() {
              return queue.isEmpty();
          }
      }
  }
  