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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.util.List;
 
 
 
Utilities for interacting with and monitoring DirectByteBuffer allocations.
 
 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) {
       .warn("Unable to initialize ObjectName for DirectByteBuffer allocations.");
     } finally {
        = n;
     }
     if ( != null) {
       s = ManagementFactory.getPlatformMBeanServer();
     }
      = s;
     if ( != null) {
       try {
       } catch (JMException e) {
         .debug("Failed to retrieve nio.BufferPool direct MemoryUsed attribute."e);
       }
     }
      = a != null;
   }

  

Returns:
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<Stringarguments = runtimemxBean.getInputArguments();
     long multiplier = 1; //for the byte case.
     for (String s : arguments) {
       if (s.contains("-XX:MaxDirectMemorySize=")) {
         String memSize = s.toLowerCase()
             .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;
  }

  

Returns:
the current amount of direct memory used.
  public static long getDirectMemoryUsage() {
    if ( == null ||  == null || !return 0;
    try {
      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.

Parameters:
toBeDestroyed The DirectByteBuffer that will be "cleaned". Utilizes reflection.
  public static void destroyDirectByteBuffer(ByteBuffer toBeDestroyed)
    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);
  }
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