content: /**
   * Copyright The Apache Software Foundation
   *
   * 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 com.alibaba.wasp.metrics;
  
  import org.apache.commons.logging.Log;
  import org.apache.commons.logging.LogFactory;
  import org.apache.hadoop.metrics2.lib.DefaultMetricsSystem;
  
  import java.util.concurrent.ScheduledFuture;
  import java.util.concurrent.TimeUnit;
  
  /**
   * JMX caches the beans that have been exported; even after the values are
   * removed from hadoop's metrics system the keys and old values will still
   * remain. This class stops and restarts the Hadoop metrics system, forcing JMX
   * to clear the cache of exported metrics.
   * 
   * This class need to be in the o.a.h.metrics2.impl namespace as many of the
   * variables/calls used are package private.
   */
  public class JmxCacheBuster {
    private static final Log LOG = LogFactory.getLog(JmxCacheBuster.class);
    private static Object lock = new Object();
    private static ScheduledFuture fut = null;
  
    /**
     * For JMX to forget about all previously exported metrics.
     */
    public static void clearJmxCache() {
  
      // If there are more then 100 ms before the executor will run then
      // everything should be merged.
      if (fut == null
          || (!fut.isDone() && fut.getDelay(TimeUnit.MILLISECONDS) > 100))
        return;
  
      synchronized (lock) {
        fut = MetricsExecutor.getExecutor().schedule(
            new JmxCacheBusterRunnable(), 5,
            TimeUnit.SECONDS);
      }
    }
  
    static class JmxCacheBusterRunnable implements Runnable {
  
      @Override
      public void run() {
        LOG.trace("Clearing JMX mbean cache.");
  
        // This is pretty extreme but it's the best way that
        // I could find to get metrics to be removed.
  
        try {
          DefaultMetricsSystem.INSTANCE.stop();
          DefaultMetricsSystem.INSTANCE.start();
        } catch (Exception exception) {
          LOG.debug(
              "error clearing the jmx it appears the metrics system hasn't been started",
              exception);
        }
      }
    }
  }
  