Messages_Between_Processes.c

/***
forker.c        R.Tervo     Jan 2013
-------------------------------------
Exploring fork() and exec()
This program monitors PID and PPID in
while spawning a second program.
-------------------------------------
***/

#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <pthread.h>
#include <sys/neutrino.h>
#define MSGSIZE 80
int chid;
int rcvid;
unsigned flags;
char send_message[MSGSIZE]; 		//send message
char receive_message[MSGSIZE]; 		//receive message
char reader[MSGSIZE]; //
char readerreply[MSGSIZE];

pid_t pidA, ppidA;       // define PID storage
pid_t pidB, ppidB;
pid_t pidC,  pid;


main( )
{


int   status;		 // status of wait()

puts("Embedded Message Passing Example Program");
puts("creating channel");
	flags = NULL;
chid = ChannelCreate(flags);
	if (chid==1){
		printf("could not create channel \n");
		//exit(1);
	}

pidA  = getpid();        // establish main program PID
ppidA = getppid();
printf("PID=%i, PPID=%i  I am the main program.\n", pidA, ppidA);

pid = wait(&status);	 // wait for child process to end (none)
printf("I am done waiting for PID[%i] with status %i\n",pid, status);

printf("Fork now..\n");
fflush(stdout);          // complete any pending prints

pidC  = fork();	         // returns child PID (or 0 if child)

pidB  = getpid();
ppidB = getppid();

if(pidA != pidB)
 {
   printf("PID=%i, PPID=%i  I am the child.  \n", pidB, ppidB);

   printf("Exec now..\n");
   fflush(stdout);          // complete any pending prints
   int ucoid;
   	puts("user has been called");
   	puts("user connecting to channel. \n");
   	ucoid = ConnectAttach(0, pidA, chid, 0, NULL);
   	while(1) {
   		puts("user:go ahead, enter a string");
   		gets(send_message);
   		printf("user:waiting to send: = %s =.\n",send_message);
   		MsgSend(ucoid, &send_message, sizeof(send_message), &receive_message, sizeof(receive_message));
   		printf("user: received a reply from friend: = %s =\n", receive_message);
   		sleep(1);
   	}
   //execl("./hello","hello",'\0');  // replace this process with another

   printf(" ...we never print this line...\n");
 } else
 {
	 int fcoid;
	 	puts("friend has been called");
	 	puts("friend connecting to channel. \n");
	 	fcoid = ConnectAttach(0, pidB, chid, 0, NULL);
	 	strcpy(readerreply, "Got it!");
	 	while(1) {
	 		printf("friend: I am waiting to receive message from user.\n");
	 		rcvid = MsgReceive(chid, &reader, sizeof(reader), NULL);
	 		printf("friend: received = %s = from user.\n", reader);
	 		MsgReply(rcvid, NULL, &readerreply, sizeof(readerreply));
	 		sleep(1);
			printf("PID=%i, PPID=%i  I am the parent. \n", pidB, ppidB);
		}

	pid = wait(&status);	 // wait for child process to end (none)
	printf("I am done waiting for PID[%i] with status %i\n",pid, status);
 }
return(0);
} // end main