Interprocess Communication Between Child And Parent C

Question

i am writing a Unix program where a father process forks a child p1.the father process handle the SIGUSR1.
the child process every 1 sec generate a random number between 1 to 9 and send to father using pipe the father Receives the number and print it to the console.when the father process catch the SIGUSR1 signal he begin to print only odd numbers and when the received number is 11 he kill the child by sending SIGTERM signal. the father wait on status and then terminate the child.

#include<stdio.h>
#include<unistd.h>
#include<stdlib.h>
#define READ_END 0
#define WRITE_END 1
volatile sig_atomic_t token;
void handle_me(int signum)
{
    token=0;
}
int main(int argc, char *argv[]){
        pid_t child1;
        token=1;
        int pipe1[2],status;
        unsigned int bufChild1,bufChild2;
        if (pipe(pipe1) == -1) 
        {
           fprintf(stderr, "Pipe failed");
        }
        child1 = fork();
        if (child1 < 0) 
        {
            fprintf(stderr, "Fork Failed");
            return 0;
        }
        else if (child1 == 0) 
        {
            printf(" child  with pid %d\n", getpid());
            printf("The Parent pid is %d\n", getppid());
            while(1) 
            {
                    bufChild1 = (unsigned int)rand()%9 +1;
                    fprintf(stdout, "generated: %u\n", bufChild1);
                    close(pipe1[READ_END]);
                    write(pipe1[WRITE_END],&bufChild1,sizeof(bufChild1)); //write into the Parent
                    close(pipe1[WRITE_END]);  
            } 
        }
        else
        {
            signal(SIGUSR1,handle_me);
            printf(" Parent Process\n");
            while(!token)
            {
                    close(pipe1[READ_END]);
                    read(pipe1[READ_END],&bufChild2,sizeof(bufChild2)); //write into the Parent
                    fprintf(stdout, "Received: %u\n", bufChild2);
                    close(pipe1[WRITE_END]);  
            }
        }
        wait(&status);
        return 1;
}

i wonder how to implement this condition when the father process catch the SIGUSR1 signal he begin to print only odd numbers and when the recieved number is 11 he kill the child by sending sigterm signal.

I Used a global variable Which can be set if SIGUSR1 is caught by the father.
i will be very thankful if someone can help me.

Armali Armali · Accepted Answer · 2016-01-08T10:24:39

The program contains some errors.

You forgot to #include <signal.h>.
To have the child process do its work every 1 second, you have to put a sleep(1) into the child's while loop.
The child must not close(pipe1[WRITE_END]); otherwise it can no longer write to parent.
The parent must not close(pipe1[READ_END]); otherwise it can no longer read from child.

i wonder how to implement this condition when the father process catch the SIGUSR1 signal he begin to print only odd numbers ...

You already implemented clearing the variable token when the signal is catched, so you could change the parent part to e. g.

            close(pipe1[WRITE_END]);  
            while (read(pipe1[READ_END], &bufChild2, sizeof bufChild2) > 0)
                if (token || bufChild2&1)
                    fprintf(stdout, "Received: %u\n", bufChild2);

... when the recieved number is 11 he kill the child by sending sigterm signal.

This will never happen, since the program generates "a random number between 1 to 9".

Interprocess Communication Between Child And Parent C

1 Answers