/**
    * Copyright 2005-2011 The Kuali Foundation
    *
    * Licensed under the Educational Community 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.opensource.org/licenses/ecl2.php
    *
   * 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.kuali.rice.krad.util;
  
  import java.lang.management.ManagementFactory;
  import java.lang.management.MemoryMXBean;
  import java.lang.management.MemoryNotificationInfo;
  import java.lang.management.MemoryPoolMXBean;
  import java.lang.management.MemoryType;
  import java.util.ArrayList;
  import java.util.Collection;
  
  import javax.management.Notification;
  import javax.management.NotificationEmitter;
  import javax.management.NotificationListener;
  
  import org.apache.log4j.Logger;
  
  public class MemoryMonitor {
      private final Collection<Listener> listeners = new ArrayList<Listener>();
      private static final Logger LOG = Logger.getLogger(MemoryMonitor.class);
      private String springContextId;
  
      public interface Listener {
          public void memoryUsageLow(String springContextId, long usedMemory, long maxMemory);
      }
  
      public MemoryMonitor() {
          LOG.info("initializing");
          this.springContextId = "Unknown";
          MemoryMXBean mbean = ManagementFactory.getMemoryMXBean();
          NotificationEmitter emitter = (NotificationEmitter) mbean;
          emitter.addNotificationListener(new NotificationListener() {
              public void handleNotification(Notification n, Object hb) {
                  if (n.getType().equals(MemoryNotificationInfo.MEMORY_THRESHOLD_EXCEEDED)) {
                      long maxMemory = tenuredGenPool.getUsage().getMax();
                      long usedMemory = tenuredGenPool.getUsage().getUsed();
                      for (Listener listener : listeners) {
                          listener.memoryUsageLow(springContextId, usedMemory, maxMemory);
                      }
                  }
              }
          }, null, null);
      }
  
      public MemoryMonitor(String springContextId) {
          this();
          this.springContextId = springContextId;
      }
  
      public boolean addListener(Listener listener) {
          return listeners.add(listener);
      }
  
      public boolean removeListener(Listener listener) {
          return listeners.remove(listener);
      }
  
      private static final MemoryPoolMXBean tenuredGenPool = findTenuredGenPool();
  
      public static void setPercentageUsageThreshold(double percentage) {
          if (percentage <= 0.0 || percentage > 1.0) {
              throw new IllegalArgumentException("percentage not in range");
          }
          long maxMemory = tenuredGenPool.getUsage().getMax();
          long warningThreshold = (long) (maxMemory * percentage);
          tenuredGenPool.setUsageThreshold(warningThreshold);
      }
  
      private static MemoryPoolMXBean findTenuredGenPool() {
          for (MemoryPoolMXBean pool : ManagementFactory.getMemoryPoolMXBeans()) {
              if (pool.getType() == MemoryType.HEAP && pool.isUsageThresholdSupported()) {
                  return pool;
              }
          }
          throw new AssertionError("could not find tenured space");
      }
  }