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.subscribers;
  
  import java.util.concurrent.CountDownLatch;
  
  import org.reactivestreams.Subscription;
  
  import io.reactivex.rxjava3.core.FlowableSubscriber;
  import io.reactivex.rxjava3.internal.subscriptions.SubscriptionHelper;
  import io.reactivex.rxjava3.internal.util.*;
  
  public abstract class BlockingBaseSubscriber<T> extends CountDownLatch
  implements FlowableSubscriber<T> {
  
      T value;
      Throwable error;
  
      Subscription upstream;
  
      volatile boolean cancelled;
  
      public BlockingBaseSubscriber() {
          super(1);
      }
  
      @Override
      public final void onSubscribe(Subscription s) {
          if (SubscriptionHelper.validate(this.upstream, s)) {
              this.upstream = s;
              if (!cancelled) {
                  s.request(Long.MAX_VALUE);
                  if (cancelled) {
                      this.upstream = SubscriptionHelper.CANCELLED;
                      s.cancel();
                  }
              }
          }
      }
  
      @Override
      public final void onComplete() {
          countDown();
      }
  
      /**
       * Block until the first value arrives and return it, otherwise
       * return null for an empty source and rethrow any exception.
       * @return the first value or null if the source is empty
       */
      public final T blockingGet() {
          if (getCount() != 0) {
              try {
                  BlockingHelper.verifyNonBlocking();
                  await();
              } catch (InterruptedException ex) {
                  Subscription s = this.upstream;
                  this.upstream = SubscriptionHelper.CANCELLED;
                  if (s != null) {
                      s.cancel();
                  }
                  throw ExceptionHelper.wrapOrThrow(ex);
              }
          }
  
          Throwable e = error;
          if (e != null) {
              throw ExceptionHelper.wrapOrThrow(e);
          }
          return value;
      }
  }
  