content: /*
   * Licensed to the Apache Software Foundation (ASF) under one or more
   * contributor license agreements. See the NOTICE file distributed with
   * this work for additional information regarding copyright ownership.
   * The ASF licenses this file to You 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 org.apache.kafka.clients.consumer.internals.events;
  
  import org.apache.kafka.clients.consumer.internals.ConsumerNetworkThread;
  import org.apache.kafka.clients.consumer.internals.metrics.AsyncConsumerMetrics;
  import org.apache.kafka.common.utils.Time;
  
  import java.util.ArrayList;
  import java.util.List;
  import java.util.Objects;
  import java.util.concurrent.BlockingQueue;
  
  /**
   * An event handler that receives {@link BackgroundEvent background events} from the
   * {@link ConsumerNetworkThread network thread} which are then made available to the application thread
   * via an {@link EventProcessor}.
   */
  
  public class BackgroundEventHandler {
  
      private final BlockingQueue<BackgroundEvent> backgroundEventQueue;
      private final Time time;
      private final AsyncConsumerMetrics asyncConsumerMetrics;
  
      public BackgroundEventHandler(final BlockingQueue<BackgroundEvent> backgroundEventQueue,
                                    final Time time,
                                    final AsyncConsumerMetrics asyncConsumerMetrics) {
          this.backgroundEventQueue = backgroundEventQueue;
          this.time = time;
          this.asyncConsumerMetrics = asyncConsumerMetrics;
      }
  
      /**
       * Add a {@link BackgroundEvent} to the handler.
       *
       * @param event A {@link BackgroundEvent} created by the {@link ConsumerNetworkThread network thread}
       */
      public void add(BackgroundEvent event) {
          Objects.requireNonNull(event, "BackgroundEvent provided to add must be non-null");
          event.setEnqueuedMs(time.milliseconds());
          asyncConsumerMetrics.recordBackgroundEventQueueSize(backgroundEventQueue.size() + 1);
          backgroundEventQueue.add(event);
      }
  
      /**
       * Drain all the {@link BackgroundEvent events} from the handler.
       *
       * @return A list of {@link BackgroundEvent events} that were drained
       */
      public List<BackgroundEvent> drainEvents() {
          List<BackgroundEvent> events = new ArrayList<>();
          backgroundEventQueue.drainTo(events);
          asyncConsumerMetrics.recordBackgroundEventQueueSize(0);
          return events;
      }
  }
  