DirectByteBuffer

DirectBuffer 通过免去中间交换的内存拷贝, 提升IO处理速度;也就是常说的zero-copy

• ByteBuffer
• HeapByteBuffer
• MappedByteBuffer
• MappedByteBuffer.map(int mode,long position,long size);

 

READ_ONLY只读试图修改得到的缓冲区将导致抛出 ReadOnlyBufferExceptionREAD_WRITE读/写对得到的缓冲区的更改最终将传播到文件；该更改对映射到同一文件的其他程序不一定是可见的PRIVATE专用对得到的缓冲区的更改不会传播到文件，并且该更改对映射到同一文件的其他程序也不是可见的；相反，会创建缓冲区已修改部分的专用副本

 

 

分配java.nio.ByteBuffer.allocateDirect释放sun.nio.ch.DirectBuffer.cleaner().clean()

 

可以通过参数 -XX:MaxDirectMemorySize= 设置其可使用的最大内存大小，当未设置时默认同 -Xmx 的大小。

各种应用

 

BigMemoryhttp://terracotta.org/products/bigmemoryBigMemory stores “big” amounts of data in machine memory for ultra-fast accessDirectMemoryhttp://incubator.apache.org/directmemory/Apache DirectMemory is a multi layered cache implementation featuring off-heap memory management (a-la BigMemory) to enable efficient handling of a large number of java objects without affecting jvm garbage collection performanceHugeCollectionshttps://code.google.com/p/vanilla-java/wiki/HugeCollectionsIf you want to efficiently store large collections of data in memory. This library can dramatically reduce Full GC times and reduce memory consumption as well

 

OutOfMemoryError

和 DirectBuffer 相关的内存泄漏参看Study_Java_HotSpot_OOME

参考资料

[1]. http://blog.csdn.net/fancyerii/article/details/7655451
[2]. http://lixjluck.iteye.com/blog/1130455
[3]. http://www.zhurouyoudu.com/index.php/archives/470/

 

import java.lang.reflect.Method;import java.nio.ByteBuffer;import java.security.AccessController;import java.security.PrivilegedAction;/** * {@link DirectByteBufferCleaner} * * @author <a href=mailto:[e-mail]>zhongl</a> * @created 2011-1-14 */public final class DirectByteBufferCleaner {  private DirectByteBufferCleaner() {}  public static void clean(final ByteBuffer byteBuffer) {    if (!byteBuffer.isDirect()) return;    try {      Object cleaner = invoke(byteBuffer, "cleaner");      invoke(cleaner, "clean");    } catch (Exception e) { /* ignore */ }  }  private static Object invoke(final Object target, String methodName) throws Exception {    final Method method = target.getClass().getMethod(methodName);    return AccessController.doPrivileged(new PrivilegedAction<Object>() {      @Override      public Object run() {        try {          return method.invoke(target);        } catch (Exception e) {          throw new RuntimeException(e);        }      }    });  }}