#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <assert.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <signal.h>

int main(int argc, char *argv[])
{
    pid_t p;
    int fd[2];
    char c;

    if (pipe(fd) == -1)
    {
        exit(1);
    }

    p = fork();
    assert(p != -1);

    int id = 0;

    if (p == 0)
    {
        id += 2;
    }

    p = fork();
    assert(p != -1);

    if (p == 0)
    {
        id += 1;
    }

    if (id == 0)
    {
        wait(NULL);
        wait(NULL);
    }

    if (id == 2)
    {
        wait(NULL);
    }


    while (id == 1)
    {
        int w = write(fd[1], &p, sizeof(pid_t));
        assert(w == sizeof(pid_t));

        printf("%d sent %d\n", p, p);

        sleep(3);
    }

    while (id == 3)
    {
        int op;
        int r = read(fd[0], &op, sizeof(pid_t));
        assert(r == sizeof(pid_t));

        printf("\t%d received %d\n", p, op);

        sleep(1);
    }
}