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

void child_main(int id, int pipefd[2], int n) {
    printf("hi %d\n", id);
    fflush(stdout);
    sigset_t mask;
    sigemptyset(&mask);
    sigaddset(&mask, SIGUSR1);
    int sigfd = signalfd(-1, &mask, 0);
    struct signalfd_siginfo siginfo;

    char buf[64];

    read(sigfd, &siginfo, sizeof siginfo);
    read(pipefd[0], buf, sizeof buf);
    pid_t other;
    {
        uintmax_t tmp;
        sscanf(buf, "%ju", &tmp);
        other = tmp;
    }

    for (;;) {
        read(sigfd, &siginfo, sizeof siginfo);
        read(pipefd[0], buf, sizeof buf);
        int num;
        sscanf(buf, "%d", &num);
        if (num > n)
            break;
        printf("%d %d\n", id, num);
        fflush(stdout);

        sprintf(buf, "%d", num+1);
        kill(other, SIGUSR1);
        write(pipefd[1], buf, sizeof buf);
        if (num == n)
            break;
    }

    exit(0);
}

int main(int argc, char **argv) {
    if (argc < 2)
        errx(1, "Usage: %s N", argv[0]);

    int n;
    sscanf(argv[1], "%d", &n);

    int pipefd[2];
    if (pipe(pipefd) == -1)
        err(1, "pipe() failed");

    pid_t child1 = fork();
    if (child1 == -1)
        err(1, "fork() failed");
    if (child1 == 0)
        child_main(1, pipefd, n);

    pid_t child2 = fork();
    if (child2 == -1)
        err(1, "fork() failed");
    if (child2 == 0)
        child_main(2, pipefd, n);

    char buf[64];

    sprintf(buf, "%ju", (uintmax_t) child2);
    kill(child1, SIGUSR1);
    write(pipefd[1], buf, sizeof buf);

    sprintf(buf, "%ju", (uintmax_t) child1);
    kill(child2, SIGUSR1);
    write(pipefd[1], buf, sizeof buf);

    kill(child1, SIGUSR1);
    sprintf(buf, "1");
    write(pipefd[1], buf, sizeof buf);

    close(pipefd[0]);
    close(pipefd[1]);

    waitpid(child1, NULL, 0);
    waitpid(child2, NULL, 0);

    exit(0);
}
sm19/5.c