/**
 * 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.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;
    }
  }
}
