java 通过 nmap 跨进程内存共享

先启动A进程，再启动B进程。

A进程：

import java.io.BufferedReader;
import java.io.File;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.RandomAccessFile;
import java.nio.ByteBuffer;
import java.nio.MappedByteBuffer;
import java.nio.channels.FileChannel;

public class ProgramA {

    public static void main(String[] args) throws IOException {
        FileChannel fileChannel = new RandomAccessFile(new File("db.data"), "rw").getChannel();
        MappedByteBuffer mappedByteBuffer = fileChannel.map(FileChannel.MapMode.READ_WRITE, 0, 8);
        
        // 写
        byte[] data = new byte[] {3,3,3,3,4,4,4,4};
        mappedByteBuffer.put(data);
        
        System.out.println("数据写入成功！");
        
        BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));
        reader.readLine();
        
        System.out.println("over");
        fileChannel.close();
    }

}

 

B进程：

import java.io.File;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.RandomAccessFile;
import java.nio.ByteBuffer;
import java.nio.MappedByteBuffer;
import java.nio.channels.FileChannel;

public class ProgramB {

    public static void main(String[] args) throws IOException {
        FileChannel fileChannel = new RandomAccessFile(new File("db.data"), "rw").getChannel();
        MappedByteBuffer mappedByteBuffer = fileChannel.map(FileChannel.MapMode.READ_WRITE, 0, 8);

        // 读
        byte[] data = new byte[8];
        ByteBuffer subBuffer = mappedByteBuffer.slice();
        subBuffer.get(data);
        System.out.println("数据读取成功:");
        System.out.println(data);
        fileChannel.close();
    }

}

 如果要从指定位置读取或写入：

MappedByteBuffer subBuffer = mappedByteBuffer.slice(); 
subBuffer.position(position); 
subBuffer.put(data);
subBuffer.sett(data);

通过测试发现，内存区没有做写同步互斥，多个进程可以同时往一块内存同时写入数据，这种使用方式可能会导致内存损坏。.getChannel().lock() 应该可以获取锁进行写同步。