ar@cello ~ % cat crustaceae.c
#include <sys/types.h>
#include <unistd.h>
#include <stdio.h>
#include <sys/wait.h>

int
do_son(int i, int inbound, int outbound)
{
    char buf[8];
    int k;

    read(inbound, buf, 1); // lock
    read(0, buf, 8);
    sscanf(buf, "%d", &k);
    write(outbound, buf, 1); // unlock

    printf("%d %d\n", i + 1, k * k);
    return 0;
}


int
main (int argc, char **argv)
{
    char token[1] = {' '};
    char buf[24];
    int f2s[2];
    int s2f[2];
    pid_t pid[3];
    int status = 0;
    if(pipe(f2s) < 0)
    {
        fprintf(stderr, "%s: %s\n", argv[0], "Could not pipe");
        return 1;
    }
    if(pipe(s2f) < 0)
    {
        fprintf(stderr, "%s: %s\n", argv[0], "Could not pipe");
        return 1;
    }
    for(int i = 0; i < 3; i++)
    {
        pid[i] = fork();
        if(pid[i] < 0)
        {
            fprintf(stderr, "%s: %s\n", argv[0], "Could not fork");
            return 1;
        }
        if(pid[i] == 0)
        {
            close(f2s[1]);
            close(s2f[0]);
            return do_son(i, f2s[0], s2f[1]);
        }
    }
    close(f2s[0]);
    close(s2f[1]);
    for(int i = 0; i < 3; i++)
    {
        /* Let's make a request... */
        write(f2s[1], token, 1);
        /* ...and wait for the response */
        read(s2f[0], token, 1);
    }
    for(int i = 0; i < 3; i++)
    {
        wait(&status);
    }
    close(f2s[1]);
    close(s2f[0]);
    return 0;
}
ar@cello ~ % gcc crustaceae.c -o crustaceae
ar@cello ~ % printf '-0036  \n  506  \n    -40\n' | ./crustaceae
3 1296
1 256036
2 1600
ar@cello ~ % printf '-0036  \n  506  \n    -40\n' | ./crustaceae
2 1296
1 256036
3 1600
ar@cello ~ % printf '-0036  \n  506  \n    -40\n' | ./crustaceae
1 1296
3 256036
2 1600
ar@cello ~ %