#include <string.h>
#include <errno.h>
#include <semaphore.h>
#include <sys/mman.h>
#include <sys/types.h>
#include <unistd.h>
#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <signal.h>
#include <time.h>

#define SIZEMAP 1

static void handler(int signal) {
    switch (signal) {
        case SIGUSR1:
        default:
            ;
    }
}

static void handler_install() {
    struct sigaction action;

    action.sa_handler = handler;
    action.sa_flags = 0;
    sigemptyset(&action.sa_mask);
    sigaction(SIGUSR1, &action, NULL);
}

void timespec_add(struct timespec * tv_a, const struct timespec * tv_b) {
    tv_a->tv_sec += tv_b->tv_sec;
    tv_a->tv_nsec += tv_b->tv_nsec;

    if (tv_a->tv_nsec > 999999999) {
        tv_a->tv_sec += 1;
        tv_a->tv_nsec -= 999999999;
    }
}

void timespec_minus(struct timespec * tv_a, const struct timespec * tv_b) {
    tv_a->tv_sec -= tv_b->tv_sec;
    tv_a->tv_nsec -= tv_b->tv_nsec;

    if (tv_a->tv_nsec < 0) {
        tv_a->tv_sec -= 1;
        tv_a->tv_nsec += 1000 * 1000 * 1000;
    }
}

int main() {
    int shm_fd;
    struct timespec* desc_map;
    struct timespec* t_temp;
    struct timespec* t_final;
    int i;

    shm_fd = shm_open("shm_testfork", O_RDWR | O_CREAT, 0666);
    if (!shm_fd) {
        fprintf(stderr, "%s(%d): %s\n", __FILE__, __LINE__, strerror(errno));
        exit(1);
    }

    if (ftruncate(shm_fd, (SIZEMAP * sizeof(struct timespec))) != 0) {
        fprintf(stderr, "%s(%d): %s\n", __FILE__, __LINE__, strerror(errno));
        exit(1);
    }

    handler_install();

    desc_map = malloc(sizeof(struct timespec));
    t_temp = malloc(sizeof(struct timespec));
    t_final = malloc(sizeof(struct timespec));

    t_final->tv_sec = 0;
    t_final->tv_nsec = 0;

    for (i = 0; i < 1000; i++) {
        clock_gettime(CLOCK_REALTIME, t_temp);
        if (fork() == 0) {
            pause();
            timespec_minus(t_temp, desc_map);
            timespec_add(t_final, t_temp);
        }
        else {
            clock_gettime(CLOCK_REALTIME, desc_map);
            kill(getppid(), SIGUSR1);
            kill(getpid(), SIGKILL);
        }
    }

    free(desc_map);
    free(t_temp);
    free(t_final);
    shm_unlink("shm_testfork");
    exit(0);
}