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1   /**
2    * Licensed to the Apache Software Foundation (ASF) under one
3    * or more contributor license agreements.  See the NOTICE file
4    * distributed with this work for additional information
5    * regarding copyright ownership.  The ASF licenses this file
6    * to you under the Apache License, Version 2.0 (the
7    * "License"); you may not use this file except in compliance
8    * with the License.  You may obtain a copy of the License at
9    *
10   *     http://www.apache.org/licenses/LICENSE-2.0
11   *
12   * Unless required by applicable law or agreed to in writing, software
13   * distributed under the License is distributed on an "AS IS" BASIS,
14   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
15   * See the License for the specific language governing permissions and
16   * limitations under the License.
17   */
18  
19  package org.apache.hadoop.metrics2.impl;
20  
21  import java.util.concurrent.ScheduledFuture;
22  import java.util.concurrent.TimeUnit;
23  
24  import org.apache.commons.logging.Log;
25  import org.apache.commons.logging.LogFactory;
26  import org.apache.hadoop.classification.InterfaceAudience;
27  import org.apache.hadoop.metrics2.MetricsExecutor;
28  import org.apache.hadoop.metrics2.lib.DefaultMetricsSystem;
29  import org.apache.hadoop.metrics2.lib.MetricsExecutorImpl;
30  
31  /**
32   * JMX caches the beans that have been exported; even after the values are removed from hadoop's
33   * metrics system the keys and old values will still remain.  This class stops and restarts the
34   * Hadoop metrics system, forcing JMX to clear the cache of exported metrics.
35   *
36   * This class need to be in the o.a.h.metrics2.impl namespace as many of the variables/calls used
37   * are package private.
38   */
39  @edu.umd.cs.findbugs.annotations.SuppressWarnings(
40      value="LI_LAZY_INIT_STATIC",
41      justification="Yeah, its weird but its what we want")
42  @InterfaceAudience.Private
43  public class JmxCacheBuster {
44    private static final Log LOG = LogFactory.getLog(JmxCacheBuster.class);
45    private static Object lock = new Object();
46    private static ScheduledFuture fut = null;
47    private static MetricsExecutor executor = new MetricsExecutorImpl();
48  
49    /**
50     * For JMX to forget about all previously exported metrics.
51     */
52    public static void clearJmxCache() {
53  
54      //If there are more then 100 ms before the executor will run then everything should be merged.
55      if (fut == null || (!fut.isDone()  && fut.getDelay(TimeUnit.MILLISECONDS) > 100)) return;
56  
57      synchronized (lock) {
58        fut = executor.getExecutor().schedule(new JmxCacheBusterRunnable(), 5, TimeUnit.SECONDS);
59      }
60    }
61  
62    static class JmxCacheBusterRunnable implements Runnable {
63  
64      @Override
65      public void run() {
66        LOG.trace("Clearing JMX mbean cache.");
67  
68        // This is pretty extreme but it's the best way that
69        // I could find to get metrics to be removed.
70        try {
71          if (DefaultMetricsSystem.instance() != null ) {
72            DefaultMetricsSystem.instance().stop();
73            DefaultMetricsSystem.instance().start();
74          }
75  
76        }  catch (Exception exception )  {
77          LOG.debug("error clearing the jmx it appears the metrics system hasn't been started", exception);
78        }
79      }
80    }
81  }