/**
    *
    * 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.ManagementFactory;
  import java.lang.management.RuntimeMXBean;
  import java.lang.reflect.InvocationTargetException;
  import java.lang.reflect.Method;
  import java.nio.ByteBuffer;
  import java.util.List;
  import java.util.Locale;
  
  import javax.management.JMException;
  import javax.management.MBeanServer;
  import javax.management.MalformedObjectNameException;
  import javax.management.ObjectName;
  
  import org.apache.commons.logging.Log;
  import org.apache.commons.logging.LogFactory;
  import org.apache.hadoop.hbase.classification.InterfaceAudience;
  import org.apache.hadoop.hbase.classification.InterfaceStability;
  
  import com.google.common.base.Preconditions;
  
  /**
   * Utilities for interacting with and monitoring DirectByteBuffer allocations.
   */
  @InterfaceAudience.Private
  @InterfaceStability.Evolving
  public class DirectMemoryUtils {
    private static final Log LOG = LogFactory.getLog(DirectMemoryUtils.class);
    private static final String MEMORY_USED = "MemoryUsed";
    private static final MBeanServer BEAN_SERVER;
    private static final ObjectName NIO_DIRECT_POOL;
    private static final boolean HAS_MEMORY_USED_ATTRIBUTE;
  
    static {
      // initialize singletons. Only maintain a reference to the MBeanServer if
      // we're able to consume it -- hence convoluted logic.
      ObjectName n = null;
      MBeanServer s = null;
      Object a = null;
      try {
        n = new ObjectName("java.nio:type=BufferPool,name=direct");
      } catch (MalformedObjectNameException e) {
        LOG.warn("Unable to initialize ObjectName for DirectByteBuffer allocations.");
      } finally {
        NIO_DIRECT_POOL = n;
      }
      if (NIO_DIRECT_POOL != null) {
        s = ManagementFactory.getPlatformMBeanServer();
      }
      BEAN_SERVER = s;
      if (BEAN_SERVER != null) {
        try {
          a = BEAN_SERVER.getAttribute(NIO_DIRECT_POOL, MEMORY_USED);
        } catch (JMException e) {
          LOG.debug("Failed to retrieve nio.BufferPool direct MemoryUsed attribute: " + e);
        }
      }
      HAS_MEMORY_USED_ATTRIBUTE = a != null;
    }
  
    /**
     * @return the setting of -XX:MaxDirectMemorySize as a long. Returns 0 if
     *         -XX:MaxDirectMemorySize is not set.
     */
    public static long getDirectMemorySize() {
      RuntimeMXBean runtimemxBean = ManagementFactory.getRuntimeMXBean();
      List<String> arguments = runtimemxBean.getInputArguments();
      long multiplier = 1; //for the byte case.
      for (String s : arguments) {
        if (s.contains("-XX:MaxDirectMemorySize=")) {
          String memSize = s.toLowerCase(Locale.ROOT)
              .replace("-xx:maxdirectmemorysize=", "").trim();
  
          if (memSize.contains("k")) {
            multiplier = 1024;
          }
  
          else if (memSize.contains("m")) {
            multiplier = 1048576;
         }
 
         else if (memSize.contains("g")) {
           multiplier = 1073741824;
         }
         memSize = memSize.replaceAll("[^\\d]", "");
 
         long retValue = Long.parseLong(memSize);
         return retValue * multiplier;
       }
     }
     return 0;
   }
 
   /**
    * @return the current amount of direct memory used.
    */
   public static long getDirectMemoryUsage() {
     if (BEAN_SERVER == null || NIO_DIRECT_POOL == null || !HAS_MEMORY_USED_ATTRIBUTE) return 0;
     try {
       Long value = (Long) BEAN_SERVER.getAttribute(NIO_DIRECT_POOL, MEMORY_USED);
       return value == null ? 0 : value;
     } catch (JMException e) {
       // should print further diagnostic information?
       return 0;
     }
   }
 
   /**
    * DirectByteBuffers are garbage collected by using a phantom reference and a
    * reference queue. Every once a while, the JVM checks the reference queue and
    * cleans the DirectByteBuffers. However, as this doesn't happen
    * immediately after discarding all references to a DirectByteBuffer, it's
    * easy to OutOfMemoryError yourself using DirectByteBuffers. This function
    * explicitly calls the Cleaner method of a DirectByteBuffer.
    * 
    * @param toBeDestroyed
    *          The DirectByteBuffer that will be "cleaned". Utilizes reflection.
    *          
    */
   public static void destroyDirectByteBuffer(ByteBuffer toBeDestroyed)
       throws IllegalArgumentException, IllegalAccessException,
       InvocationTargetException, SecurityException, NoSuchMethodException {
 
     Preconditions.checkArgument(toBeDestroyed.isDirect(),
         "toBeDestroyed isn't direct!");
 
     Method cleanerMethod = toBeDestroyed.getClass().getMethod("cleaner");
     cleanerMethod.setAccessible(true);
     Object cleaner = cleanerMethod.invoke(toBeDestroyed);
     Method cleanMethod = cleaner.getClass().getMethod("clean");
     cleanMethod.setAccessible(true);
     cleanMethod.invoke(cleaner);
   }
 }