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.agent.stomp;
  
  import java.util.concurrent.BlockingQueue;
  import java.util.concurrent.Executors;
  import java.util.concurrent.LinkedBlockingQueue;
  import java.util.concurrent.ScheduledExecutorService;
  import java.util.concurrent.ThreadFactory;
  import java.util.concurrent.TimeUnit;
  
  import org.apache.ambari.server.configuration.Configuration;
  import org.slf4j.Logger;
  import org.slf4j.LoggerFactory;
  
  import com.google.common.util.concurrent.ThreadFactoryBuilder;
  import com.google.inject.Injector;
  
  /**
   * Simultaneous processing a lot of registering/topology/metadata etc. requests from agents during
   * agent registration can cause response timeout on agents' side. So it is allowed to process simultaneously requests
   * only from limited number of agents with session ids from {@link registrationQueue}. Queue has limited capacity,
   * session id can able be appeared in queue with agent connecting to server and releases with first heartbeat or disconnect from
   * server.
   */
  public class AgentsRegistrationQueue {
    private static final Logger LOG = LoggerFactory.getLogger(AgentsRegistrationQueue.class);
    private final BlockingQueue<String> registrationQueue;
    private final ThreadFactory threadFactoryExecutor = new ThreadFactoryBuilder().setNameFormat("agents-queue-%d").build();
    private final ScheduledExecutorService scheduledExecutorService = Executors.newScheduledThreadPool(1, threadFactoryExecutor);
  
    public AgentsRegistrationQueue(Injector injector) {
      Configuration configuration = injector.getInstance(Configuration.class);
      registrationQueue = new LinkedBlockingQueue<>(configuration.getAgentsRegistrationQueueSize());
    }
  
    public boolean offer(String sessionId) {
      boolean offered = registrationQueue.offer(sessionId);
      scheduledExecutorService.schedule(new CompleteJob(sessionId, registrationQueue), 60, TimeUnit.SECONDS);
      return offered;
    }
  
    public void complete(String sessionId) {
      registrationQueue.remove(sessionId);
    }
  
    private class CompleteJob implements Runnable {
      private String sessionId;
      private BlockingQueue<String> registrationQueue;
  
      public CompleteJob(String sessionId, BlockingQueue<String> registrationQueue) {
        this.sessionId = sessionId;
        this.registrationQueue = registrationQueue;
      }
  
      @Override
      public void run() {
        registrationQueue.remove(sessionId);
      }
    }
  }
  