kqueue/kqtimer.c

   1 /*
   2  * Compile with:
   3  * gcc kqtimer.c -o kqtimer -Wall -W -Wextra -ansi -pedantic
   4  *
   5  * The following code will setup a timer that will trigger a
   6  * kevent every 5 seconds. Once it does, the process will fork
   7  * and the child will execute the date(1) command.
   8  */
   9
  10 #include <sys/event.h>
  11 #include <sys/time.h>
  12 #include <stdio.h>
  13 #include <stdlib.h>
  14 #include <string.h>   /* for strerror() */
  15 #include <unistd.h>
  16
  17 /* Function prototypes */
  18 void diep(const char *s);
  19
  20 int main(void)
  21 {
  22     struct kevent change;    /* event we want to monitor */
  23     struct kevent event;     /* event that was triggered */
  24     pid_t pid;
  25     int kq, nev;
  26
  27     /* Create a new kernel event queue */
  28     if ((kq = kqueue()) == -1)
  29         diep("kqueue()");
  30
  31     /* Initalise kevent structure */
  32     EV_SET(&change, 1, EVFILT_TIMER, EV_ADD | EV_ENABLE, 0, 5000, 0);
  33
  34     /* Loop forever */
  35     for (;;) {
  36         nev = kevent(kq, &change, 1, &event, 1, NULL);
  37
  38         if (nev < 0)
  39             diep("kevent()");
  40
  41         else if (nev > 0) {
  42             if (event.flags & EV_ERROR) {   /* report any error */
  43                 fprintf(stderr, "EV_ERROR: %s\n", strerror(event.data));
  44                 exit(EXIT_FAILURE);
  45             }
  46
  47             if ((pid = fork()) < 0)         /* fork error */
  48                 diep("fork()");
  49
  50             else if (pid == 0)              /* child */
  51                 if (execlp("date", "date", (char *)0) < 0)
  52                     diep("execlp()");
  53         }
  54     }
  55
  56     /* Close kqueue */
  57     if (close(kq) == -1)
  58         diep("close()");
  59
  60     return EXIT_SUCCESS;
  61 }
  62
  63 void diep(const char *s)
  64 {
  65     perror(s);
  66     exit(EXIT_FAILURE);
  67 }