minix/lib/libsys/timers.c

   1 /*
   2  * Watchdog timer management. These functions in this file provide a
   3  * convenient interface to the timers library that manages a list of
   4  * watchdog timers. All details of scheduling an alarm at the CLOCK task
   5  * are hidden behind this interface.
   6  *
   7  * The entry points into this file are:
   8  *   init_timer:     initialize a timer structure
   9  *   set_timer:      reset and existing or set a new watchdog timer
  10  *   cancel_timer:   remove a timer from the list of timers
  11  *   expire_timers:  check for expired timers and run watchdog functions
  12  *
  13  */
  14
  15 #include "syslib.h"
  16 #include <minix/timers.h>
  17 #include <minix/sysutil.h>
  18
  19 static minix_timer_t *timers = NULL;
  20 static int expiring = FALSE;
  21
  22 /*
  23  * Initialize the timer 'tp'.
  24  */
  25 void
  26 init_timer(minix_timer_t * tp)
  27 {
  28
  29         tmr_inittimer(tp);
  30 }
  31
  32 /*
  33  * Set the timer 'tp' to trigger 'ticks' clock ticks in the future.  When it
  34  * triggers, call function 'watchdog' with argument 'arg'.  The given timer
  35  * object must have been initialized with init_timer(3) already.  The given
  36  * number of ticks must be between 0 and TMRDIFF_MAX inclusive.  A ticks value
  37  * of zero will cause the alarm to trigger on the next clock tick.  If the
  38  * timer was already set, it will be canceled first.
  39  */
  40 void
  41 set_timer(minix_timer_t *tp, clock_t ticks, tmr_func_t watchdog, int arg)
  42 {
  43         clock_t prev_time, next_time;
  44         int r, had_timers;
  45
  46         if (ticks > TMRDIFF_MAX)
  47                 panic("set_timer: ticks value too large: %u", (int)ticks);
  48
  49         /* Add the timer to the list. */
  50         had_timers = tmrs_settimer(&timers, tp, getticks() + ticks, watchdog,
  51             arg, &prev_time, &next_time);
  52
  53         /* Reschedule our synchronous alarm if necessary. */
  54         if (!expiring && (!had_timers || next_time != prev_time)) {
  55                 if ((r = sys_setalarm(next_time, TRUE /*abs_time*/)) != OK)
  56                         panic("set_timer: couldn't set alarm: %d", r);
  57         }
  58 }
  59
  60 /*
  61  * Cancel the timer 'tp'.  The timer object must have been initialized with
  62  * init_timer(3) first.  If the timer was not set before, the call is a no-op.
  63  */
  64 void
  65 cancel_timer(minix_timer_t * tp)
  66 {
  67         clock_t next_time, prev_time;
  68         int r, have_timers;
  69
  70         if (!tmr_is_set(tp))
  71                 return;
  72
  73         have_timers = tmrs_clrtimer(&timers, tp, &prev_time, &next_time);
  74
  75         /*
  76          * If the earliest timer has been removed, we have to set the alarm to
  77          * the next timer, or cancel the alarm altogether if the last timer
  78          * has been canceled.
  79          */
  80         if (!expiring) {
  81                 if (!have_timers)
  82                         r = sys_setalarm(0, FALSE /*abs_time*/);
  83                 else if (prev_time != next_time)
  84                         r = sys_setalarm(next_time, TRUE /*abs_time*/);
  85                 else
  86                         r = OK;
  87
  88                 if (r != OK)
  89                         panic("cancel_timer: couldn't set alarm: %d", r);
  90         }
  91 }
  92
  93 /*
  94  * Expire all timers that were set to expire before/at the given current time.
  95  */
  96 void
  97 expire_timers(clock_t now)
  98 {
  99         clock_t next_time;
 100         int r, have_timers;
 101
 102         /*
 103          * Check for expired timers. Use a global variable to indicate that
 104          * watchdog functions are called, so that sys_setalarm() isn't called
 105          * more often than necessary when set_timer or cancel_timer are called
 106          * from these watchdog functions.
 107          */
 108         expiring = TRUE;
 109         have_timers = tmrs_exptimers(&timers, now, &next_time);
 110         expiring = FALSE;
 111
 112         /* Reschedule an alarm if necessary. */
 113         if (have_timers) {
 114                 if ((r = sys_setalarm(next_time, TRUE /*abs_time*/)) != OK)
 115                         panic("expire_timers: couldn't set alarm: %d", r);
 116         }
 117 }