kqueue/kqtimer.c

   1 /* compile with:
   2    gcc kqtimer.c -o kqtimer -Wall -W -Wextra -ansi -pedantic
   3
   4    The following code will setup a timer that will trigger a
   5    kevent every 5 seconds. Once it does, the process will fork
   6    and the child will execute the date(1) command.
   7 */
   8
   9 #include <sys/event.h>
  10 #include <sys/time.h>
  11 #include <stdio.h>
  12 #include <stdlib.h>
  13 #include <string.h>   /* for strerror() */
  14 #include <unistd.h>
  15
  16 /* function prototypes */
  17 void diep(const char *s);
  18
  19 int main(void)
  20 {
  21     struct kevent change;    /* event we want to monitor */
  22     struct kevent event;     /* event that was triggered */
  23     pid_t pid;
  24     int kq, nev;
  25
  26     /* create a new kernel event queue */
  27     if ((kq = kqueue()) == -1)
  28         diep("kqueue()");
  29
  30     /* initalise kevent structure */
  31     EV_SET(&change, 1, EVFILT_TIMER, EV_ADD | EV_ENABLE, 0, 5000, 0);
  32
  33     /* loop forever */
  34     for (;;) {
  35         nev = kevent(kq, &change, 1, &event, 1, NULL);
  36
  37         if (nev < 0)
  38             diep("kevent()");
  39
  40         else if (nev > 0) {
  41             if (event.flags & EV_ERROR) {   /* report any error */
  42                 fprintf(stderr, "EV_ERROR: %s\n", strerror(event.data));
  43                 exit(EXIT_FAILURE);
  44             }
  45
  46             if ((pid = fork()) < 0)         /* fork error */
  47                 diep("fork()");
  48
  49             else if (pid == 0)              /* child */
  50                 if (execlp("date", "date", (char *)0) < 0)
  51                     diep("execlp()");
  52         }
  53     }
  54
  55     close(kq);
  56     return EXIT_SUCCESS;
  57 }
  58
  59 void diep(const char *s)
  60 {
  61     perror(s);
  62     exit(EXIT_FAILURE);
  63 }