Introduction to DIPC

DIPC (Distributed Inter-Process Communication) is a software-only solution for transparent distributed data exchange on a network of Linux computers. It operates at the kernel level, and allows developers to use System V semaphores, message queues, and shared memory segments over a network. Its distributed shared memory (DSM) system provides strict consistency. Minimal source code changes are needed to let applications exchange data over a network.

You can read the paper Transparent Distributed Programming under Linux for more information on DIPC. More papers are available here.

The DIPC package contains detailed documentation about the system, as well as examples and the complete source code. To download DIPC please click here and select the download tab. Alternatively, visit this download page.

Using DIPC requires patching the Linux kernel. After that, distributed data exchange is very easy. For example, a process can start by sending data to a message queue with a given ID number. In normal System V IPC, this data is only available to processes running within the same computer, but with DIPC, a process running in another machine can receive the message. As simple as that.

The source code at the end of this page allows two processes to use DIPC to transfer a message over the network. The code is as in the usual System V IPC programming. The small addition required by DIPC is highlighted in bold.

Kamran Karimi can be contacted at kamkar@users.sourceforge.net.

The sample program that follows sends 512 bytes (containing a message) from one process to another via a message queue. If run on a cluster with DIPC properly installed, the message will traverse the network.

A few notes about DIPC programs: They can be run on computers with no support for DIPC in the kernel, though in this case all the processes should run in the same machine. DIPC does not distribute any code across the network, so the user must start each process remotely as appropriate (maybe via 'rsh' or similar methods).

/*
* hello.h
*
* Header file for hello1.c and hello2.c
*
* By Kamran Karimi
*/

#include <stdio.h>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/msg.h>
#include <errno.h>
#include <linux/dipc.h>
#include <string.h>


#ifdef __GLIBC__
#define IPC_DIPC 00010000 /* make it distributed */
#endif


#define MSG_KEY 40
#define MSG_MODE (IPC_DIPC | IPC_EXCL | 0777)
/* use of 'IPC_DIPC' is the ONLY thing that makes this program a distributed
   one. Everything else is normal System V IPC programming */
#define MSG_TYPE 10
#define MSG_SIZE 512

struct message
{
   long mtype;
   char mtext[MSG_SIZE];
};


/*
* hello1.c
*
* It initializes a message structure and waits to receive a message.
* After running hello1, you should run hello2 on a remote machine.
*
* By Kamran Karimi
*/

#include "hello.h"

int main()
{
  int msgid;
  struct message mess;

  /* create the message queue. The other process will access it later */
  msgid = msgget(MSG_KEY, MSG_MODE | IPC_CREAT);
  if(msgid < 0)
  {
   fprintf(stderr,"Hello1: msgget() failed BECAUSE %s\n", strerror(errno));
   exit(20);
  }
  fprintf(stderr,"Hello1: waiting to receive a message...\n");
  if(msgrcv(msgid, (struct msgbuf *)&mess, sizeof(mess.mtext), 0, 0) < 0)
   fprintf(stderr,"Hello1: msgrcv() failed BECAUSE %s\n", strerror(errno));
  else
   fprintf(stderr,"Hello1: Received '%s'\n",mess.mtext);
  msgctl(msgid,IPC_RMID,NULL);
  exit(0);
}


/*
* hello2.c
*
* This program sends a message to hello1 process.
* You should first run hello1, and then hello2 on a machine in the
* same cluster
*
* By Kamran Karimi
*/

#include "hello.h"

int main()
{
  int msgid;
  struct message mess;

  /* gain access to the message queue that was created by hello1 */
  msgid = msgget(MSG_KEY, MSG_MODE);
  if(msgid < 0)
  {
   fprintf(stderr,"Hello2: msgget() failed BECAUSE %s\n",strerror(errno));
   exit(20);
  }
  mess.mtype = MSG_TYPE; /* not necessary here */
  strcpy(mess.mtext,"Hello, Distributed Programming!");
  /* now send the message. This will traverse the network if hello1 and
    hello2 programs are in different computers and DIPC is properly
    installed */
  if(msgsnd(msgid, (struct msgbuf *)&mess, sizeof(mess.mtext), 0) < 0)
  {
   fprintf(stderr,"Hello2: msgsnd() failed BECAUSE %s\n", strerror(errno));
   exit(20);
  }
  exit(0);
}