三种零拷贝的实现以及对比
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，如果想了解几种零拷贝的底层原理实现的理论知识的话，可以看看下面这篇文章
链接: 深入理解零拷贝技术
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\\Desktop\\ioTest.txt");
if(!file.exists()){
file.createNewFile();
}
FileOutputStream fileOutputStream = 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 start = 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：" + (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();
}
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