servers/pm/timers.c

   1 /* PM watchdog timer management. These functions in this file provide
   2  * a convenient interface to the timers library that manages a list of
   3  * watchdog timers. All details of scheduling an alarm at the CLOCK task
   4  * are hidden behind this interface.
   5  * Only system processes are allowed to set an alarm timer at the kernel.
   6  * Therefore, the PM maintains a local list of timers for user processes
   7  * that requested an alarm signal.
   8  *
   9  * The entry points into this file are:
  10  *   pm_set_timer:      reset and existing or set a new watchdog timer
  11  *   pm_expire_timers:  check for expired timers and run watchdog functions
  12  *   pm_cancel_timer:   remove a time from the list of timers
  13  *
  14  */
  15
  16 #include "pm.h"
  17
  18 #include <timers.h>
  19 #include <minix/syslib.h>
  20 #include <minix/com.h>
  21
  22 PRIVATE timer_t *pm_timers = NULL;
  23 PRIVATE int pm_expiring = 0;
  24
  25 /*===========================================================================*
  26  *                              pm_set_timer                                 *
  27  *===========================================================================*/
  28 PUBLIC void pm_set_timer(timer_t *tp, int ticks, tmr_func_t watchdog, int arg)
  29 {
  30         int r;
  31         clock_t now, prev_time = 0, next_time;
  32
  33         if ((r = getuptime(&now)) != OK)
  34                 panic("PM couldn't get uptime");
  35
  36         /* Set timer argument and add timer to the list. */
  37         tmr_arg(tp)->ta_int = arg;
  38         prev_time = tmrs_settimer(&pm_timers,tp,now+ticks,watchdog,&next_time);
  39
  40         /* Reschedule our synchronous alarm if necessary. */
  41         if (pm_expiring == 0 && (! prev_time || prev_time > next_time)) {
  42                 if (sys_setalarm(next_time, 1) != OK)
  43                         panic("PM set timer couldn't set alarm");
  44         }
  45
  46         return;
  47 }
  48
  49 /*===========================================================================*
  50  *                              pm_expire_timers                             *
  51  *===========================================================================*/
  52 PUBLIC void pm_expire_timers(clock_t now)
  53 {
  54         clock_t next_time;
  55
  56         /* Check for expired timers. Use a global variable to indicate that
  57          * watchdog functions are called, so that sys_setalarm() isn't called
  58          * more often than necessary when pm_set_timer or pm_cancel_timer are
  59          * called from these watchdog functions. */
  60         pm_expiring = 1;
  61         tmrs_exptimers(&pm_timers, now, &next_time);
  62         pm_expiring = 0;
  63
  64         /* Reschedule an alarm if necessary. */
  65         if (next_time > 0) {
  66                 if (sys_setalarm(next_time, 1) != OK)
  67                         panic("PM expire timer couldn't set alarm");
  68         }
  69 }
  70
  71 /*===========================================================================*
  72  *                              pm_cancel_timer                              *
  73  *===========================================================================*/
  74 PUBLIC void pm_cancel_timer(timer_t *tp)
  75 {
  76         clock_t next_time, prev_time;
  77         prev_time = tmrs_clrtimer(&pm_timers, tp, &next_time);
  78
  79         /* If the earliest timer has been removed, we have to set the alarm to
  80      * the next timer, or cancel the alarm altogether if the last timer has
  81      * been cancelled (next_time will be 0 then).
  82          */
  83         if (pm_expiring == 0 && (prev_time < next_time || ! next_time)) {
  84                 if (sys_setalarm(next_time, 1) != OK)
  85                         panic("PM expire timer couldn't set alarm");
  86         }
  87 }