Just started learning about pipes (IPC in general). After I went through some man pages, websites and few SO questions like this, This and few others. I got to know the basic and I see that this communication is done only once, i.e., parent writes to child and child reads it or parent and child reads and writes to each other just once and then the pipe closes.
What I want is keep this communication between the processes without the pipe closing, i.e., say, my program has 2 child processes where 1st child process is running something in a while loop and the 2nd is running a timer continuously. At certain intervals, my 2nd process sends some 'signal' to 1st child and my 1st stops and prints something at that instant and restarts again for next timer stop. (<-This I have done using threads)
This is the program that I tried just as a sample. But I'm not able to keep the communication continuous.
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/types.h>
int main(void)
{
int fd[2], nbytes, count = 5;
pid_t childpid;
char string[] = "Hello, world!\n";
char readbuffer[80];
if((childpid = fork()) == -1)
{
perror("fork");
exit(1);
}
if(childpid == 0)
{
/* Child process closes up input side of pipe */
/* Send "string" through the output side of pipe */
while(count--)
{
pipe(fd);
close(fd[0]);
write(fd[1], string, (strlen(string)+1));
close(fd[1]);
}
exit(0);
}
else
{
/* Parent process closes up output side of pipe */
while(count--)
{
pipe(fd);
close(fd[1]);
/* Read in a string from the pipe */
nbytes = read(fd[0], readbuffer, sizeof(readbuffer));
printf("Received string: %s\n", readbuffer);
close(fd[0]);
close(fd[1]);
}
}
int status;
waitpid(getppid(), &status, 0);
printf("Done!\n");
return(0);
}
From those example, I inferred that the pipe get's closed after each send/read. I tried opening new pipe every time, still I could't get it.
Can anyone please help me what am I missing or what should I do?
