linux之eventfd()

#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 (0)

int main(int argc, char **argv)
{
    int efd, j;
    uint64_t u;
    ssize_t s;

    if (argc < 2)
    {
        fprintf(stderr, "Usage: %s <num>...\n", argv[0]);
        exit(EXIT_FAILURE);
    }

    efd = eventfd(0, 0);
    if (efd == -1)
    {
        handle_error("eventfd");
    }

    switch (fork())
    {
        case 0:
            for (j = 1; j < argc; j++)
            {
                printf("Child writing %s to efd\n", argv[j]);
                u = strtoull(argv[j], NULL, 0);
                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 -1:
            handle_error("fork");

        default:
            sleep(2);

            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);
    }
}