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 org.reactivestreams.Subscription;
  
  import io.reactivex.rxjava3.annotations.NonNull;
  import io.reactivex.rxjava3.core.FlowableSubscriber;
  import io.reactivex.rxjava3.internal.subscriptions.SubscriptionHelper;
  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 FlowableStageSubscriber<T> extends CompletableFuture<T> implements FlowableSubscriber<T> {
  
      final AtomicReference<Subscription> upstream = new AtomicReference<>();
  
      T value;
  
      @Override
      public final void onSubscribe(@NonNull Subscription s) {
          if (SubscriptionHelper.setOnce(upstream, s)) {
              afterSubscribe(s);
          }
      }
  
      protected abstract void afterSubscribe(Subscription s);
  
      @Override
      public final void onError(Throwable t) {
          clear();
          if (!completeExceptionally(t)) {
              RxJavaPlugins.onError(t);
          }
      }
  
      protected final void cancelUpstream() {
          SubscriptionHelper.cancel(upstream);
      }
  
      protected final void clear() {
          value = null;
          upstream.lazySet(SubscriptionHelper.CANCELLED);
      }
  
      @Override
      public final boolean cancel(boolean mayInterruptIfRunning) {
          cancelUpstream();
          return super.cancel(mayInterruptIfRunning);
      }
  
      @Override
      public final boolean complete(T value) {
          cancelUpstream();
          return super.complete(value);
      }
  
      @Override
      public final boolean completeExceptionally(Throwable ex) {
          cancelUpstream();
          return super.completeExceptionally(ex);
      }
  }
  