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.jdk8;
  
  import java.util.concurrent.CompletableFuture;
  import java.util.concurrent.atomic.AtomicReference;
  
  import io.reactivex.rxjava3.annotations.NonNull;
  import io.reactivex.rxjava3.core.Observer;
  import io.reactivex.rxjava3.disposables.Disposable;
  import io.reactivex.rxjava3.internal.disposables.DisposableHelper;
  import io.reactivex.rxjava3.plugins.RxJavaPlugins;
  
  /**
   * Base class that extends CompletableFuture and provides basic infrastructure
   * to notify watchers upon upstream signals.
   * @param <T> the element type
   * @since 3.0.0
   */
  abstract class ObservableStageObserver<T> extends CompletableFuture<T> implements Observer<T> {
  
      final AtomicReference<Disposable> upstream = new AtomicReference<>();
  
      T value;
  
      @Override
      public final void onSubscribe(@NonNull Disposable d) {
          DisposableHelper.setOnce(upstream, d);
      }
  
      @Override
      public final void onError(Throwable t) {
          clear();
          if (!completeExceptionally(t)) {
              RxJavaPlugins.onError(t);
          }
      }
  
      protected final void disposeUpstream() {
          DisposableHelper.dispose(upstream);
      }
  
      protected final void clear() {
          value = null;
          upstream.lazySet(DisposableHelper.DISPOSED);
      }
  
      @Override
      public final boolean cancel(boolean mayInterruptIfRunning) {
          disposeUpstream();
          return super.cancel(mayInterruptIfRunning);
      }
  
      @Override
      public final boolean complete(T value) {
          disposeUpstream();
          return super.complete(value);
      }
  
      @Override
      public final boolean completeExceptionally(Throwable ex) {
          disposeUpstream();
          return super.completeExceptionally(ex);
      }
  }
  