001/*
002 * Licensed to the Apache Software Foundation (ASF) under one
003 * or more contributor license agreements.  See the NOTICE file
004 * distributed with this work for additional information
005 * regarding copyright ownership.  The ASF licenses this file
006 * to you under the Apache License, Version 2.0 (the
007 * "License"); you may not use this file except in compliance
008 * with the License.  You may obtain a copy of the License at
009 *
010 *     http://www.apache.org/licenses/LICENSE-2.0
011 *
012 * Unless required by applicable law or agreed to in writing, software
013 * distributed under the License is distributed on an "AS IS" BASIS,
014 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
015 * See the License for the specific language governing permissions and
016 * limitations under the License.
017 */
018package org.apache.hadoop.metrics2.impl;
019
020import java.util.concurrent.ScheduledFuture;
021import java.util.concurrent.TimeUnit;
022import java.util.concurrent.atomic.AtomicBoolean;
023import java.util.concurrent.atomic.AtomicReference;
024import org.apache.hadoop.metrics2.MetricsExecutor;
025import org.apache.hadoop.metrics2.lib.DefaultMetricsSystem;
026import org.apache.hadoop.metrics2.lib.MetricsExecutorImpl;
027import org.apache.hadoop.util.StringUtils;
028import org.apache.yetus.audience.InterfaceAudience;
029import org.slf4j.Logger;
030import org.slf4j.LoggerFactory;
031
032/**
033 * JMX caches the beans that have been exported; even after the values are removed from hadoop's
034 * metrics system the keys and old values will still remain. This class stops and restarts the
035 * Hadoop metrics system, forcing JMX to clear the cache of exported metrics. This class need to be
036 * in the o.a.h.metrics2.impl namespace as many of the variables/calls used are package private.
037 */
038@InterfaceAudience.Private
039public final class JmxCacheBuster {
040  private static final Logger LOG = LoggerFactory.getLogger(JmxCacheBuster.class);
041  private static AtomicReference<ScheduledFuture> fut = new AtomicReference<>(null);
042  private static MetricsExecutor executor = new MetricsExecutorImpl();
043  private static AtomicBoolean stopped = new AtomicBoolean(false);
044
045  private JmxCacheBuster() {
046    // Static only cache.
047  }
048
049  /**
050   * For JMX to forget about all previously exported metrics.
051   */
052  public static void clearJmxCache() {
053    if (LOG.isTraceEnabled()) {
054      LOG.trace("clearing JMX Cache" + StringUtils.stringifyException(new Exception()));
055    }
056    // If there are more then 100 ms before the executor will run then everything should be merged.
057    ScheduledFuture future = fut.get();
058    if ((future != null && (!future.isDone() && future.getDelay(TimeUnit.MILLISECONDS) > 100))) {
059      // BAIL OUT
060      return;
061    }
062    if (stopped.get()) {
063      return;
064    }
065    future = executor.getExecutor().schedule(new JmxCacheBusterRunnable(), 5, TimeUnit.SECONDS);
066    fut.set(future);
067  }
068
069  /**
070   * Stops the clearing of JMX metrics and restarting the Hadoop metrics system. This is needed for
071   * some test environments where we manually inject sources or sinks dynamically.
072   */
073  public static void stop() {
074    stopped.set(true);
075    ScheduledFuture future = fut.get();
076    future.cancel(false);
077  }
078
079  /**
080   * Restarts the stopped service.
081   * @see #stop()
082   */
083  public static void restart() {
084    stopped.set(false);
085  }
086
087  final static class JmxCacheBusterRunnable implements Runnable {
088    @Override
089    public void run() {
090      if (LOG.isTraceEnabled()) {
091        LOG.trace("Clearing JMX mbean cache.");
092      }
093
094      // This is pretty extreme but it's the best way that
095      // I could find to get metrics to be removed.
096      try {
097        if (DefaultMetricsSystem.instance() != null) {
098          DefaultMetricsSystem.instance().stop();
099          // Sleep some time so that the rest of the hadoop metrics
100          // system knows that things are done
101          Thread.sleep(500);
102          DefaultMetricsSystem.instance().start();
103        }
104      } catch (Exception exception) {
105        LOG.debug("error clearing the jmx it appears the metrics system hasn't been started",
106          exception);
107      }
108    }
109  }
110}