/**
    * 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.hadoop.hbase.ipc;
  
  import org.apache.hadoop.conf.Configuration;
  import org.apache.hadoop.hbase.DaemonThreadFactory;
  
  import java.io.IOException;
  import java.util.concurrent.ArrayBlockingQueue;
  import java.util.concurrent.ThreadPoolExecutor;
  import java.util.concurrent.TimeUnit;
  import java.util.concurrent.atomic.AtomicInteger;
  
  /**
   * A very simple {@code }RpcScheduler} that serves incoming requests in order.
   *
   * This can be used for HMaster, where no prioritization is needed.
   */
  public class FifoRpcScheduler extends RpcScheduler {
    private final int handlerCount;
    private final int maxQueueLength;
    private final AtomicInteger queueSize = new AtomicInteger(0);
    private ThreadPoolExecutor executor;
  
    public FifoRpcScheduler(Configuration conf, int handlerCount) {
      this.handlerCount = handlerCount;
      this.maxQueueLength = conf.getInt(RpcScheduler.IPC_SERVER_MAX_CALLQUEUE_LENGTH,
          handlerCount * RpcServer.DEFAULT_MAX_CALLQUEUE_LENGTH_PER_HANDLER);
    }
  
    @Override
    public void init(Context context) {
      // no-op
    }
  
    @Override
    public void start() {
      this.executor = new ThreadPoolExecutor(
          handlerCount,
          handlerCount,
          60,
          TimeUnit.SECONDS,
          new ArrayBlockingQueue<Runnable>(maxQueueLength),
          new DaemonThreadFactory("FifoRpcScheduler.handler"),
          new ThreadPoolExecutor.CallerRunsPolicy());
    }
  
    @Override
    public void stop() {
      this.executor.shutdown();
    }
  
    @Override
    public boolean dispatch(final CallRunner task) throws IOException, InterruptedException {
      // Executors provide no offer, so make our own.
      int queued = queueSize.getAndIncrement();
      if (maxQueueLength > 0 && queued >= maxQueueLength) {
        queueSize.decrementAndGet();
        return false;
      }
      executor.submit(new Runnable() {
        @Override
        public void run() {
          task.setStatus(RpcServer.getStatus());
          task.run();
          queueSize.decrementAndGet();
        }
      });
      return true;
    }
  
    @Override
    public int getGeneralQueueLength() {
      return executor.getQueue().size();
    }
  
    @Override
    public int getPriorityQueueLength() {
      return 0;
    }
  
    @Override
    public int getReplicationQueueLength() {
      return 0;
   }
 
   @Override
   public int getActiveRpcHandlerCount() {
     return executor.getActiveCount();
   }
 
   @Override
   public long getNumGeneralCallsDropped() {
     return 0;
   }
 
   @Override
   public long getNumLifoModeSwitches() {
     return 0;
   }
 }