目录
- 简介
- 传统实现
- MMAP
- transferTo
- 堆外内存
- 总结
简介
本文主要是介绍几种零拷贝的实现示例,以及与最传统的做一个对比,看看在效率上到底有多大的提升
好了,废话不多说直接干,本章例子是通过网络IO传输一个8M大小的文件,对比传输效率,由于服务端接收端不需要修改,所以我们先上服务端代码:
public static void main(String[] args) throws IOException { ServerSocket serverSocket = new ServerSocket(8080); System.out.println("服务端:等待连接"); Socket accept = serverSocket.accept(); System.out.println("服务端:" + accept.getRemoteSocketAddress() + "已连接"); File file = new File("C:\\Users\\Administrator编程客栈\\Desktop\\ioTest.txt"); if(!file.exists()){ file.createNewFile(); } FileOutputStream fil编程客栈eOutputStream = new FileOutputStream(file); InputStream bufferedInputStream = accept.getInputStream(); byte[] bytes = new byte[2048]; int read; while ((read = bufferedInputStream.read(bytes,0,2048)) != -1) { fileOutputStream.write(bytes); } OutputStream outputStream = accept.getOutputStream(); outputStream.write("接收完毕".getBytes()); accept.shutdownOutput(); fileOutputStream.close(); outputStream.close(); bufferedInputStream.close(); accept.close(); }
传统实现
正常的socket传输,耗时:46ms
public static void normal() throws IOException { Socket socket = new Socket("127.0.0.1", 8080); OutputStream outputStream = socket.getOutputStream(); InputStream inputStream = socket.getInputStream(); long star编程t = System.currentTimeMillis(); File file = new File("C:\\Users\\Administrator\\Desktop\\222.txt"); FileInputStream fileInputStream = new FileInputStream(file); byte[] bytes1 = new byte[2048]; while (fileInputStream.read(bytes1, 0, 2048) != -1) { outputStream.write(bytes1); } socket.shutdownOutput(); System.out.println("耗时:" + (System.currentTimeMillis() - start)); byte[] bytes = new byte[1024]; String message = ""; int read; while ((read = inputStream.read(bytes)) != -1) { message += new String(bytes, 0, read); } System.out.println("服务端发来消息->" + message); inputStream.close(); outputStream.close(); socket.close(); }
MMAP
MMAP原理就是建立了一个文件映射,划分了一个虚拟空间,往这个空间写数据,少了一次拷贝
缺点:空间有限
实践案例:RocketMq
耗时:32ms
public static void mmp() throws IOException { SocketChannel socketChannel = SocketChannel.open(); socketChannel.connect(new InetSocketAddress("127.0.0.1", 8080)); long start = System.currentTimeMillis(); Path path = Paths.get("C:\\Users\\Administrator\\Desktop\\222.txt"); FileChannel open = FileChannel.open(path, StandardOpenOption.READ); MappedByteBuffer map = open.map(FileChannel.MapMode.READ_ONLY, 0, open.size()); socketChannel.write(map); socketChannel.shutdownOutput(); System.out.println("耗时:" + (System.currentTimeMillis() - start)); ByteBuffer allocate = ByteBuffer.allocate(1024); int read = socketChannel.read(allocate); if (read > 0) { allocate.flip(); byte[] bytes = new byte[allocate.remaining()]; allocate.get(bytes); System.out.println("服务端发来消息:" + new String(bytes)); } socketChannel.close(); }
transferTo
原理就是两个通道之间直接传输数据,根据系统支持程度,少了1-2次拷贝
缺点:局限于文件通道
实践案例:Netty、Kafka
耗时:18ms
public static void transferTo() throws IOException { SocketChannel socketChannel = SocketChannel.open(); socketChannel.connect(new InetSocketAddress("127.0.0.1", 8080)); long start = System.currentTimeMillis(); Path path = Paths.get("C:\\Users\\Administrator\\Desktop\\222.txt"); FileChannel open = FileChannel.open(path, StandardOpenOption.READ); long l = open.transferTo(0, open.size(), socketChannel); socketChannel.shutdownOutput(); System.out.println("耗时:" + (Sy编程客栈stem.currentTimeMillis() - start)); ByteBuffer allocate = ByteBuffer.allocate(1024); int read = socketChannel.read(allocate); if (read > 0) { allocate.flip(); byte[] bytes = new byte[allocate.remaining()]; allocate.get(bytes); System.out.println("服务端发来消息:" + n编程客栈ew String(bytes)); } socketChannel.close(); }
堆外内存
原理直接使用堆外内存,少了一次拷贝
缺点:堆外内存开启耗时,此内存不受JVM控制,如垃圾回收等
实践案例:Netty
耗时:26ms
public static void outSide() throws IOException { SocketChannel socketChannel = SocketChannel.open(); socketChannel.connect(new InetSocketAddress("127.0.0.1", 8080)); long start = System.currentTimeMillis(); Path path = Paths.get("C:\\Users\\Administrator\\Desktop\\222.txt"); FileChannel open = FileChannel.open(path, StandardOpenOption.READ); ByteBuffer byteBuffer = ByteBuffer.allocateDirect((int) open.size()); open.read(byteBuffer); byteBuffer.flip(); socketChannel.write(byteBuffer); socketChannel.shutdownOutput(); System.out.println("耗时:" + (System.currentTimeMillis() - start)); ByteBuffer allocate = ByteBuffer.allocate(1024); int read = socketChannel.read(allocate); if (read > 0) { allocate.flip(); byte[] bytes = new byte[allocate.remaining()]; allocate.get(bytes); System.out.println("服务端发来消息:" + new String(bytes)); } socketChannel.close(); }
总结
耗时统计不完全准确,都是多次取平均,具体使用哪种需要看场景来
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