/**
    * 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.metrics2.lib;
  
  import java.util.concurrent.ScheduledExecutorService;
  import java.util.concurrent.ScheduledThreadPoolExecutor;
  import java.util.concurrent.ThreadFactory;
  import java.util.concurrent.atomic.AtomicInteger;
  
  import org.apache.hadoop.hbase.classification.InterfaceAudience;
  import org.apache.hadoop.metrics2.MetricsExecutor;
  
  /**
   *  Class to handle the ScheduledExecutorService{@link ScheduledExecutorService} used by MetricMutableQuantiles{@link MetricMutableQuantiles}
   */
  @InterfaceAudience.Private
  public class MetricsExecutorImpl implements MetricsExecutor {
  
    @Override
    public ScheduledExecutorService getExecutor() {
      return ExecutorSingleton.INSTANCE.scheduler;
    }
  
    @Override
    public void stop() {
      if (!getExecutor().isShutdown()) {
        getExecutor().shutdown();
      }
    }
  
    private enum ExecutorSingleton {
      INSTANCE;
  
      private final ScheduledExecutorService scheduler = new ScheduledThreadPoolExecutor(1, new ThreadPoolExecutorThreadFactory("HBase-Metrics2-"));
    }
  
    private static class ThreadPoolExecutorThreadFactory implements ThreadFactory {
      private final String name;
      private final AtomicInteger threadNumber = new AtomicInteger(1);
  
      private ThreadPoolExecutorThreadFactory(String name) {
        this.name = name;
      }
  
      @Override
      public Thread newThread(Runnable runnable) {
        Thread t = new Thread(runnable, name + threadNumber.getAndIncrement());
        t.setDaemon(true);
        return t;
      }
    }
  }