minix/lib/libsys/tickdelay.c

   1 #include "sysutil.h"
   2 #include <minix/timers.h>
   3
   4 /*===========================================================================*
   5  *                               tickdelay                                   *
   6  *===========================================================================*/
   7 int tickdelay(clock_t ticks)
   8 {
   9 /* This function uses the synchronous alarm to delay for a while. This works
  10  * even if a previous synchronous alarm was scheduled, because the remaining
  11  * ticks of the previous alarm are returned so that it can be rescheduled.
  12  * Note however that a long tick delay (longer than the remaining time of the
  13  * previous) alarm will also delay the previous alarm.
  14  */
  15     clock_t time_left, uptime;
  16     message m;
  17     int r, status;
  18
  19     if (ticks <= 0) return OK;          /* check for robustness */
  20
  21     /* Set the new alarm while getting the time left on the previous alarm. */
  22     if ((r = sys_setalarm2(ticks, FALSE, &time_left, &uptime)) != OK)
  23         return r;
  24
  25     /* Await synchronous alarm.  Since an alarm notification may already have
  26      * been dispatched by the time that we set the new alarm, we keep going
  27      * until we actually receive an alarm with a timestamp no earlier than the
  28      * alarm time we expect.
  29      */
  30     while ((r = ipc_receive(CLOCK, &m, &status)) == OK) {
  31         if (m.m_type == NOTIFY_MESSAGE &&
  32             m.m_notify.timestamp >= uptime + ticks)
  33                 break;
  34     }
  35
  36     /* Check if we must reschedule the previous alarm. */
  37     if (time_left != TMR_NEVER) {
  38         if (time_left > ticks)
  39                 time_left -= ticks;
  40         else
  41                 time_left = 1; /* force an alarm */
  42
  43         /* There's no point in returning an error from here.. */
  44         (void)sys_setalarm(time_left, FALSE);
  45     }
  46
  47     return r;
  48 }