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.flowable;
  
  import java.util.concurrent.atomic.AtomicReference;
  
  import org.reactivestreams.Subscriber;
  
  import io.reactivex.rxjava3.core.*;
  import io.reactivex.rxjava3.disposables.Disposable;
  import io.reactivex.rxjava3.internal.disposables.DisposableHelper;
  import io.reactivex.rxjava3.internal.subscribers.SinglePostCompleteSubscriber;
  import io.reactivex.rxjava3.internal.subscriptions.SubscriptionHelper;
  
  /**
   * Subscribe to a main Flowable first, then when it completes normally, subscribe to a Single,
   * signal its success value followed by a completion or signal its error as is.
   * <p>History: 2.1.10 - experimental
   * @param <T> the element type of the main source and output type
   * @since 2.2
   */
  public final class FlowableConcatWithSingle<T> extends AbstractFlowableWithUpstream<T, T> {
  
      final SingleSource<? extends T> other;
  
      public FlowableConcatWithSingle(Flowable<T> source, SingleSource<? extends T> other) {
          super(source);
          this.other = other;
      }
  
      @Override
      protected void subscribeActual(Subscriber<? super T> s) {
          source.subscribe(new ConcatWithSubscriber<>(s, other));
      }
  
      static final class ConcatWithSubscriber<T>
      extends SinglePostCompleteSubscriber<T, T>
      implements SingleObserver<T> {
  
          private static final long serialVersionUID = -7346385463600070225L;
  
          final AtomicReference<Disposable> otherDisposable;
  
          SingleSource<? extends T> other;
  
          ConcatWithSubscriber(Subscriber<? super T> actual, SingleSource<? extends T> other) {
              super(actual);
              this.other = other;
              this.otherDisposable = new AtomicReference<>();
          }
  
          @Override
          public void onSubscribe(Disposable d) {
              DisposableHelper.setOnce(otherDisposable, d);
          }
  
          @Override
          public void onNext(T t) {
              produced++;
              downstream.onNext(t);
          }
  
          @Override
          public void onError(Throwable t) {
              downstream.onError(t);
          }
  
          @Override
          public void onSuccess(T t) {
              complete(t);
          }
  
          @Override
          public void onComplete() {
              upstream = SubscriptionHelper.CANCELLED;
              SingleSource<? extends T> ss = other;
              other = null;
              ss.subscribe(this);
          }
  
          @Override
          public void cancel() {
              super.cancel();
              DisposableHelper.dispose(otherDisposable);
          }
      }
  }
  