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.ambari.server.events.publishers;
  
  import java.util.ArrayList;
  import java.util.List;
  import java.util.Objects;
  import java.util.concurrent.ConcurrentLinkedQueue;
  import java.util.concurrent.Executors;
  import java.util.concurrent.ScheduledExecutorService;
  import java.util.concurrent.TimeUnit;
  
  import org.apache.ambari.server.events.STOMPEvent;
  
  import com.google.common.eventbus.EventBus;
  
  public abstract class BufferedUpdateEventPublisher<T> {
  
    private static final long TIMEOUT = 1000L;
    private final ConcurrentLinkedQueue<T> buffer = new ConcurrentLinkedQueue<>();
  
    public abstract STOMPEvent.Type getType();
  
    private ScheduledExecutorService scheduledExecutorService;
  
    public BufferedUpdateEventPublisher(STOMPUpdatePublisher stompUpdatePublisher) {
      stompUpdatePublisher.registerPublisher(this);
    }
  
    public void publish(T event, EventBus m_eventBus) {
      if (scheduledExecutorService == null) {
        scheduledExecutorService =
            Executors.newScheduledThreadPool(1);
        scheduledExecutorService
            .scheduleWithFixedDelay(getScheduledPublisher(m_eventBus), TIMEOUT, TIMEOUT, TimeUnit.MILLISECONDS);
      }
      buffer.add(event);
    }
  
    protected MergingRunnable getScheduledPublisher(EventBus m_eventBus) {
      return new MergingRunnable(m_eventBus);
    }
  
    protected List<T> retrieveBuffer() {
      List<T> bufferContent = new ArrayList<>();
      while (!buffer.isEmpty()) {
        bufferContent.add(buffer.poll());
      }
      return bufferContent;
    }
  
    public abstract void mergeBufferAndPost(List<T> events, EventBus m_eventBus);
  
    private class MergingRunnable implements Runnable {
  
      private final EventBus m_eventBus;
  
      public MergingRunnable(EventBus m_eventBus) {
        this.m_eventBus = m_eventBus;
      }
  
      @Override
      public final void run() {
        List<T> events = retrieveBuffer();
        if (events.isEmpty()) {
          return;
        }
        mergeBufferAndPost(events, m_eventBus);
      }
    }
  
    @Override
    public boolean equals(Object o) {
      if (this == o) return true;
      if (o == null || getClass() != o.getClass()) return false;
      BufferedUpdateEventPublisher<?> that = (BufferedUpdateEventPublisher<?>) o;
      return Objects.equals(getType(), that.getType());
    }
  
    @Override
    public int hashCode() {
      return Objects.hash(getType());
    }
  }
  