How to do Inter process communication in Java? MemoryMapped File Example Tutorial

Hello guys, in the past, I have shown you how to do inter-thread communication in Java using wait-notify, and today, I will teach you how to do inter-process communication in Java. There are many ways to do inter-process communication in Java, you can use Sockets, both TCP and UDP, you can use RMI (Remote Method Invocation), you can use web services, or you can use memory-mapped file. The socket is the most common way of achieving inter-process communication if two processes are in two different hosts and connected via a network. RMI and WebService can also be used for similar purposes, but the last one, inter-process communication using memory-mapped files, is particularly useful if you are communicating with other processes in the same host, sharing the same memory and file system.

You can use a memory-mapped file to talk to another Java process or C/C++ process because they share the same memory. It is also the fastest way to share data between two processes, more rapid than using loopback sockets.

In a multi-core system, two processes can run on separate cores, and if you are really doing fast data sharing, you also need a mechanism to tell JVM that it's time to flush CPU cache, using a static volatile variable is an excellent way to say that, alternatively you can use Thread.sleep() to give some time to JVM to update CPU cache.

Btw, if you are serious about building a high-performance Java application then I also recommend you check out these Java Multithreading and Concurrency courses which is a great course for experienced Java programmers. You will learn tips and tricks to create highly concurrent and fast Java applications.

How to do Interprocess communication in Java? Example

Here is a code example of two processes communicating with each other using a Memory Mapped file in Java. 

Process 1 which is producing data :

import java.io.IOException;
import java.io.RandomAccessFile;
import java.nio.MappedByteBuffer;
import java.nio.channels.FileChannel;

/**
 * Inter process communication in Java using memory mapped file
 *
 * @author WINDOWS 8
 */

public class Producer {

    public static void main(String args[]) throws IOException, InterruptedException {

        RandomAccessFile rd = new RandomAccessFile("C:/temp/mapped.txt", "rw");

        FileChannel fc = rd.getChannel();
        MappedByteBuffer mem = fc.map(FileChannel.MapMode.READ_WRITE, 0, 1000);

        try {
            Thread.sleep(10000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
     
        for(int i=1; i            mem.put( (byte) i);
            System.out.println("Process 1 : " + (byte)i );
            Thread.sleep(1); // time to allow CPU cache refreshed
        }
    }
}

Output
Process 1: 1
Process 1: 2
Process 1 : 3
Process 1: 4
Process 1: 5
Process 1: 6
Process 1: 7
Process 1: 8
Process 1: 9

And here is a diagram that shows how this whole thing is working together:

Process 2, which is consuming data

import java.io.IOException;
import java.io.RandomAccessFile;
import java.nio.MappedByteBuffer;
import java.nio.channels.FileChannel;

/**
 * Inter process communication in Java using memory mapped file
 *
 * @author WINDOWS 8
 */

public class Consumer {

    public static void main(String args[]) throws IOException {

        RandomAccessFile rd = new RandomAccessFile("C:/temp/mapped.txt", "r");

        FileChannel fc = rd.getChannel();
        MappedByteBuffer mem = fc.map(FileChannel.MapMode.READ_ONLY, 0, 1000);
     
        try {
            Thread.sleep(10000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
     
     
        int value = mem.get();
        while(value != 0){
            System.out.println("Process 2 : " + value);
            value = mem.get();
        }
    }
}


Output
Process 2: 1
Process 2: 2
Process 2 : 3
Process 2: 4
Process 2: 5
Process 2: 6
Process 2: 7
Process 2: 8
Process 2: 9

That's all about how to do inter-process communication in Java. In this article, you have learned how to use a Memory-mapped file for inter-process communication in Java. This program not only teaches you how to do inter-process communication but also how to use the memory-mapped files in Java which can be used for fast read and write operations. Many Java programmers also use that as a cache in Java. 

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