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 io.reactivex.rxjava3.plugins.RxJavaPlugins;
  
  /**
   * Blocks until the upstream signals its first value or completes.
   *
   * @param <T> the value type
   */
  public final class BlockingFirstSubscriber<T> extends BlockingBaseSubscriber<T> {
  
      @Override
      public void onNext(T t) {
          if (value == null) {
              value = t;
              upstream.cancel();
              countDown();
          }
      }
  
      @Override
      public void onError(Throwable t) {
          if (value == null) {
              error = t;
          } else {
              RxJavaPlugins.onError(t);
          }
          countDown();
      }
  }
  