/*
    * 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.hbase.util;
  
  import java.lang.management.GarbageCollectorMXBean;
  import java.lang.management.ManagementFactory;
  import java.util.List;
  import java.util.Map;
  import java.util.Set;
  
  import org.apache.commons.logging.Log;
  import org.apache.commons.logging.LogFactory;
  import org.apache.hadoop.hbase.classification.InterfaceAudience;
  import org.apache.hadoop.conf.Configuration;
  
  import com.google.common.base.Joiner;
  import com.google.common.base.Preconditions;
  import com.google.common.base.Stopwatch;
  import com.google.common.collect.Lists;
  import com.google.common.collect.Maps;
  import com.google.common.collect.Sets;
  
  /**
   * Class which sets up a simple thread which runs in a loop sleeping
   * for a short interval of time. If the sleep takes significantly longer
   * than its target time, it implies that the JVM or host machine has
   * paused processing, which may cause other problems. If such a pause is
   * detected, the thread logs a message.
   * The original JvmPauseMonitor is:
   * ${hadoop-common-project}/hadoop-common/src/main/java/org/apache/hadoop/util/
   * JvmPauseMonitor.java
   * r1503806 | cmccabe | 2013-07-17 01:48:24 +0800 (Wed, 17 Jul 2013) | 1 line
   * HADOOP-9618.  thread which detects GC pauses(Todd Lipcon)
   */
  @InterfaceAudience.Private
  public class JvmPauseMonitor {
    private static final Log LOG = LogFactory.getLog(JvmPauseMonitor.class);
  
    /** The target sleep time */
    private static final long SLEEP_INTERVAL_MS = 500;
    
    /** log WARN if we detect a pause longer than this threshold */
    private final long warnThresholdMs;
    private static final String WARN_THRESHOLD_KEY =
        "jvm.pause.warn-threshold.ms";
    private static final long WARN_THRESHOLD_DEFAULT = 10000;
    
    /** log INFO if we detect a pause longer than this threshold */
    private final long infoThresholdMs;
    private static final String INFO_THRESHOLD_KEY =
        "jvm.pause.info-threshold.ms";
    private static final long INFO_THRESHOLD_DEFAULT = 1000;
  
    private Thread monitorThread;
    private volatile boolean shouldRun = true;
  
    public JvmPauseMonitor(Configuration conf) {
      this.warnThresholdMs = conf.getLong(WARN_THRESHOLD_KEY, WARN_THRESHOLD_DEFAULT);
      this.infoThresholdMs = conf.getLong(INFO_THRESHOLD_KEY, INFO_THRESHOLD_DEFAULT);
    }
    
    public void start() {
      Preconditions.checkState(monitorThread == null, "Already started");
      monitorThread = new Thread(new Monitor(), "JvmPauseMonitor");
      monitorThread.setDaemon(true);
      monitorThread.start();
    }
  
    public void stop() {
      shouldRun = false;
      monitorThread.interrupt();
      try {
        monitorThread.join();
      } catch (InterruptedException e) {
        Thread.currentThread().interrupt();
      }
    }
    
    private String formatMessage(long extraSleepTime, Map<String, GcTimes> gcTimesAfterSleep,
        Map<String, GcTimes> gcTimesBeforeSleep) {
  
      Set<String> gcBeanNames = Sets.intersection(gcTimesAfterSleep.keySet(),
        gcTimesBeforeSleep.keySet());
      List<String> gcDiffs = Lists.newArrayList();
     for (String name : gcBeanNames) {
       GcTimes diff = gcTimesAfterSleep.get(name).subtract(gcTimesBeforeSleep.get(name));
       if (diff.gcCount != 0) {
         gcDiffs.add("GC pool '" + name + "' had collection(s): " + diff.toString());
       }
     }
 
     String ret = "Detected pause in JVM or host machine (eg GC): " + "pause of approximately "
         + extraSleepTime + "ms\n";
     if (gcDiffs.isEmpty()) {
       ret += "No GCs detected";
     } else {
       ret += Joiner.on("\n").join(gcDiffs);
     }
     return ret;
   }
   
   private Map<String, GcTimes> getGcTimes() {
     Map<String, GcTimes> map = Maps.newHashMap();
     List<GarbageCollectorMXBean> gcBeans = ManagementFactory.getGarbageCollectorMXBeans();
     for (GarbageCollectorMXBean gcBean : gcBeans) {
       map.put(gcBean.getName(), new GcTimes(gcBean));
     }
     return map;
   }
 
   private static class GcTimes {
     private GcTimes(GarbageCollectorMXBean gcBean) {
       gcCount = gcBean.getCollectionCount();
       gcTimeMillis = gcBean.getCollectionTime();
     }
 
     private GcTimes(long count, long time) {
       this.gcCount = count;
       this.gcTimeMillis = time;
     }
 
     private GcTimes subtract(GcTimes other) {
       return new GcTimes(this.gcCount - other.gcCount, this.gcTimeMillis - other.gcTimeMillis);
     }
 
     @Override
     public String toString() {
       return "count=" + gcCount + " time=" + gcTimeMillis + "ms";
     }
 
     private long gcCount;
     private long gcTimeMillis;
   }
 
   private class Monitor implements Runnable {
     @Override
     public void run() {
       Stopwatch sw = new Stopwatch();
       Map<String, GcTimes> gcTimesBeforeSleep = getGcTimes();
       while (shouldRun) {
         sw.reset().start();
         try {
           Thread.sleep(SLEEP_INTERVAL_MS);
         } catch (InterruptedException ie) {
           return;
         }
         long extraSleepTime = sw.elapsedMillis() - SLEEP_INTERVAL_MS;
         Map<String, GcTimes> gcTimesAfterSleep = getGcTimes();
 
         if (extraSleepTime > warnThresholdMs) {
           LOG.warn(formatMessage(extraSleepTime, gcTimesAfterSleep, gcTimesBeforeSleep));
         } else if (extraSleepTime > infoThresholdMs) {
           LOG.info(formatMessage(extraSleepTime, gcTimesAfterSleep, gcTimesBeforeSleep));
         }
 
         gcTimesBeforeSleep = gcTimesAfterSleep;
       }
     }
   }
 
   /**
    * Simple 'main' to facilitate manual testing of the pause monitor.
    * 
    * This main function just leaks memory into a list. Running this class
    * with a 1GB heap will very quickly go into "GC hell" and result in
    * log messages about the GC pauses.
    */
   public static void main(String []args) throws Exception {
     new JvmPauseMonitor(new Configuration()).start();
     List<String> list = Lists.newArrayList();
     int i = 0;
     while (true) {
       list.add(String.valueOf(i++));
     }
   }
 }