#include <sys/eventfd.h>

#include <unistd.h>

#include <stdlib.h>

#include <stdio.h>

#include <stdint.h> /* Definition of uint64_t */

#define handle_error(msg) \

    do { perror(msg); exit(EXIT_FAILURE); } while ()

int main(int argc, char **argv)

{

    int efd, j;

    uint64_t u;

    ssize_t s;

    if (argc < )

    {

        fprintf(stderr, "Usage: %s <num>...\n", argv[]);

        exit(EXIT_FAILURE);

    }

    efd = eventfd(, );

    if (efd == -)

    {

        handle_error("eventfd");

    }

    switch (fork())

    {

        case :

            for (j = ; j < argc; j++)

            {

                printf("Child writing %s to efd\n", argv[j]);

                u = strtoull(argv[j], NULL, );

                s = write(efd, &u, sizeof(uint64_t));

                if (s != sizeof(uint64_t))

                {

                    handle_error("write");

                }

            }

            printf("Child completed write loop\n");

            exit(EXIT_SUCCESS);

        case -:

            handle_error("fork");

        default:

            sleep();

            printf("Parent about to read\n");

            s = read(efd, &u, sizeof(uint64_t));

            if (s != sizeof(uint64_t))

            {

                handle_error("read");

            }

            printf("Parent read %llu (0x%llx) from efd\n", (unsigned long long)u, (unsigned long long)u);

            exit(EXIT_SUCCESS);

    }

}