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.mixed;
  
  import java.util.concurrent.atomic.AtomicInteger;
  
  import org.reactivestreams.Subscription;
  
  import io.reactivex.rxjava3.core.FlowableSubscriber;
  import io.reactivex.rxjava3.exceptions.*;
  import io.reactivex.rxjava3.internal.subscriptions.SubscriptionHelper;
  import io.reactivex.rxjava3.internal.util.*;
  import io.reactivex.rxjava3.operators.QueueFuseable;
  import io.reactivex.rxjava3.operators.QueueSubscription;
  import io.reactivex.rxjava3.operators.SimpleQueue;
  import io.reactivex.rxjava3.operators.SpscArrayQueue;
  
  /**
   * Base class for implementing concatMapX main subscribers.
   *
   * @param <T> the upstream value type
   * @since 3.0.10
   */
  public abstract class ConcatMapXMainSubscriber<T> extends AtomicInteger
  implements FlowableSubscriber<T> {
  
      private static final long serialVersionUID = -3214213361171757852L;
  
      final AtomicThrowable errors;
  
      final int prefetch;
  
      final ErrorMode errorMode;
  
      SimpleQueue<T> queue;
  
      Subscription upstream;
  
      volatile boolean done;
  
      volatile boolean cancelled;
  
      boolean syncFused;
  
      public ConcatMapXMainSubscriber(int prefetch, ErrorMode errorMode) {
          this.errorMode = errorMode;
          this.errors = new AtomicThrowable();
          this.prefetch = prefetch;
      }
  
      @Override
      public final void onSubscribe(Subscription s) {
          if (SubscriptionHelper.validate(upstream, s)) {
              upstream = s;
              if (s instanceof QueueSubscription) {
                  @SuppressWarnings("unchecked")
                  QueueSubscription<T> qs = (QueueSubscription<T>)s;
                  int mode = qs.requestFusion(QueueFuseable.ANY | QueueFuseable.BOUNDARY);
                  if (mode == QueueFuseable.SYNC) {
                      queue = qs;
                      syncFused = true;
                      done = true;
  
                      onSubscribeDownstream();
  
                      drain();
                      return;
                  }
                  else if (mode == QueueFuseable.ASYNC) {
                      queue = qs;
  
                      onSubscribeDownstream();
  
                      upstream.request(prefetch);
                      return;
                  }
              }
  
              queue = new SpscArrayQueue<>(prefetch);
              onSubscribeDownstream();
              upstream.request(prefetch);
          }
      }
  
      @Override
      public final void onNext(T t) {
          // In async fusion mode, t is a drain indicator
          if (t != null) {
              if (!queue.offer(t)) {
                  upstream.cancel();
                  onError(new QueueOverflowException());
                  return;
              }
          }
          drain();
      }
  
      @Override
      public final void onError(Throwable t) {
          if (errors.tryAddThrowableOrReport(t)) {
              if (errorMode == ErrorMode.IMMEDIATE) {
                  disposeInner();
              }
              done = true;
              drain();
          }
      }
  
      @Override
      public final void onComplete() {
          done = true;
          drain();
      }
  
      final void stop() {
          cancelled = true;
          upstream.cancel();
          disposeInner();
          errors.tryTerminateAndReport();
          if (getAndIncrement() == 0) {
              queue.clear();
              clearValue();
          }
      }
  
      /**
       * Override this to clear values when the downstream disposes.
       */
      void clearValue() {
      }
  
      /**
       * Typically, this should be {@code downstream.onSubscribe(this);}.
       */
      abstract void onSubscribeDownstream();
  
      /**
       * Typically, this should be {@code inner.dispose()}.
       */
      abstract void disposeInner();
  
      /**
       * Implement the serialized inner subscribing and value emission here.
       */
      abstract void drain();
  }
  