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Commit 7ea70971 authored by Zach Johnson's avatar Zach Johnson Committed by Andre Eisenbach
Browse files

Rewrite alarm to avoid drift in the periodic version 

Also improve names of some functions.

Change-Id: Ia5aeebc8226ce5c36abdd372ea4de5195314e273
parent 378235a0

system/osi/src/alarm.c

+22 −17
Original line number Diff line number Diff line
@@ -37,10 +37,11 @@ struct alarm_t { 
  // a guarantee to its caller that the callback will not be in progress when it

  // returns.

  pthread_mutex_t callback_lock;

  period_ms_t created;

  period_ms_t period;

  period_ms_t deadline;

  bool is_periodic;

  alarm_callback_t callback;

  bool periodic;

  period_ms_t period;

  void *data;

};
@@ -65,9 +66,9 @@ static bool timer_set; 
static bool lazy_initialize(void);

static period_ms_t now(void);

static void alarm_set_internal(alarm_t *alarm, period_ms_t deadline, alarm_callback_t cb, void *data, bool is_periodic);

static void schedule(alarm_t *alarm, period_ms_t deadline);

static void schedule_next_instance(alarm_t *alarm);

static void timer_callback(void *data);

static void reschedule(void);

static void reschedule_root_alarm(void);



alarm_t *alarm_new(void) {

  // Make sure we have a list we can insert alarms into.
@@ -124,19 +125,20 @@ void alarm_set_periodic(alarm_t *alarm, period_ms_t period, alarm_callback_t cb, 
}



// Runs in exclusion with alarm_cancel and timer_callback.

static void alarm_set_internal(alarm_t *alarm, period_ms_t deadline, alarm_callback_t cb, void *data, bool is_periodic) {

static void alarm_set_internal(alarm_t *alarm, period_ms_t period, alarm_callback_t cb, void *data, bool is_periodic) {

  assert(alarms != NULL);

  assert(alarm != NULL);

  assert(cb != NULL);



  pthread_mutex_lock(&monitor);



  alarm->periodic = is_periodic;

  alarm->period = deadline;

  alarm->created = now();

  alarm->is_periodic = is_periodic;

  alarm->period = period;

  alarm->callback = cb;

  alarm->data = data;



  schedule(alarm, deadline);

  schedule_next_instance(alarm);



  pthread_mutex_unlock(&monitor);

}
@@ -155,7 +157,7 @@ void alarm_cancel(alarm_t *alarm) { 
  alarm->data = NULL;



  if (needs_reschedule)

    reschedule();

    reschedule_root_alarm();



  pthread_mutex_unlock(&monitor);
@@ -191,14 +193,17 @@ static period_ms_t now(void) { 
}



// Must be called with monitor held

static void schedule(alarm_t *alarm, period_ms_t deadline) {

static void schedule_next_instance(alarm_t *alarm) {

  // If the alarm is currently set and it's at the start of the list,

  // we'll need to re-schedule since we've adjusted the earliest deadline.

  bool needs_reschedule = (!list_is_empty(alarms) && list_front(alarms) == alarm);

  if (alarm->callback)

    list_remove(alarms, alarm);



  alarm->deadline = now() + deadline;

  // Calculate the next deadline for this alarm

  period_ms_t just_now = now();

  period_ms_t ms_into_period = alarm->is_periodic ? ((just_now - alarm->created) % alarm->period) : 0;

  alarm->deadline = just_now + (alarm->period - ms_into_period);



  // Add it into the timer list sorted by deadline (earliest deadline first).

  if (list_is_empty(alarms) || ((alarm_t *)list_front(alarms))->deadline >= alarm->deadline)
@@ -214,7 +219,7 @@ static void schedule(alarm_t *alarm, period_ms_t deadline) { 


  // If the new alarm has the earliest deadline, we need to re-evaluate our schedule.

  if (needs_reschedule || (!list_is_empty(alarms) && list_front(alarms) == alarm))

    reschedule();

    reschedule_root_alarm();

}



// Warning: this function is called in the context of an unknown thread.
@@ -231,7 +236,7 @@ static void timer_callback(void *ptr) { 
  // The alarm was cancelled before we got to it. Release the monitor

  // lock and exit right away since there's nothing left to do.

  if (!alarm_valid) {

    reschedule();

    reschedule_root_alarm();

    pthread_mutex_unlock(&monitor);

    return;

  }
@@ -239,10 +244,10 @@ static void timer_callback(void *ptr) { 
  alarm_callback_t callback = alarm->callback;

  void *data = alarm->data;



  if (alarm->periodic) {

    schedule(alarm, alarm->period);

  if (alarm->is_periodic) {

    schedule_next_instance(alarm);

  } else {

    reschedule();

    reschedule_root_alarm();



    alarm->deadline = 0;

    alarm->callback = NULL;
@@ -259,7 +264,7 @@ static void timer_callback(void *ptr) { 
}



// NOTE: must be called with monitor lock.

static void reschedule(void) {

static void reschedule_root_alarm(void) {

  assert(alarms != NULL);



  bool timer_was_set = timer_set;