inter jvm communication [closed]

Question

I am looking for an inter-process communication library in Java. I am looking to send small messages between JVMs and would like to do it using shared memory if I could.

Answer 1

Java NIO has support for memory-mapped files. If multiple JVMs memory-map the same file they can use it as shared memory.

Here is an example of memory mapping a file.

try {
int shmSize = 1024;
RandomAccessFile file = new RandomAccessFile("shm.raw","rw");

// inialize file size
if(file.length() < shmSize) {
  byte[] tmp = new byte[shmSize];
  file.write(tmp);
  file.seek(0); // seek back to start of file.
}

// memory-map file.
FileChannel ch = file.getChannel();
MappedByteBuffer shm = ch.map(FileChannel.MapMode.READ_WRITE, 0, shmSize);
ch.close(); // channel not needed anymore.
shm.load(); // force file into physical memory.

// now use the ByteBuffer's get/put/position methods to read/write the shared memory

} catch(Exception e) { e.printStackTrace(); }

On Linux you can create the shm.raw file in /dev/shm/ a memory based filesystem. This will help avoid any disk I/O.

For more details read this article Introduction to Memory-Mapped IO in Java

Also you will still need a way to syncronize read/writes to the shared memory. The sender JVM will need to signal the receiver JVM when a complete message has been written.

Using Java NIO's SocketChannel might be better for small messages since the receiver can be notified when a message is received. Shared memory will only really help when sending large messages.

For IPC between JVMs on different machines try JIPC

Answer 2

I would suggest you to take a look on Terracotta. I don't know if it will fit your requirements, because Terracotta's main goal is seamless scalability ("api" is just memory access), but it certainly has messaging integration module. It is opensource.

Cheers.