Rewrite alarms to use a single posix timer instance

This means we lose the ability to send the intended alarm
as context with the posix timer, but this can be handled
gracefully enough by making sure we actually have an
expired alarm at the front of the list when the timer
callback occurs.

Change-Id: I909195b5c3155075096328c529655eeb5b7d80d0

diff --git a/osi/src/alarm.c b/osi/src/alarm.c
index f8f732e..d229ce9 100644 (file)
--- a/osi/src/alarm.c
+++ b/osi/src/alarm.c
@@ -177,6 +177,15 @@ static bool lazy_initialize(void) {
     return false;
   }
 
+  struct sigevent sigevent;
+  memset(&sigevent, 0, sizeof(sigevent));
+  sigevent.sigev_notify = SIGEV_THREAD;
+  sigevent.sigev_notify_function = (void (*)(union sigval))timer_callback;
+  if (timer_create(CLOCK_ID, &sigevent, &timer) == -1) {
+    LOG_ERROR("%s unable to create timer: %s", __func__, strerror(errno));
+    return false;
+  }
+
   return true;
 }
 
@@ -225,22 +234,23 @@ static void schedule_next_instance(alarm_t *alarm) {
 // Warning: this function is called in the context of an unknown thread.
 // As a result, it must be thread-safe relative to other operations on
 // the alarm list.
-static void timer_callback(void *ptr) {
-  alarm_t *alarm = (alarm_t *)ptr;
-  assert(alarm != NULL);
-
+static void timer_callback(UNUSED_ATTR void *ptr) {
   pthread_mutex_lock(&monitor);
 
-  bool alarm_valid = list_remove(alarms, alarm);
+  alarm_t *alarm;
 
-  // 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) {
+  // Take into account that the alarm may get cancelled before we get to it.
+  // We're done here if there are no alarms or the alarm at the front is in
+  // the future. Release the monitor lock and exit right away since there's
+  // nothing left to do.
+  if (list_is_empty(alarms) || (alarm = list_front(alarms))->deadline > now()) {
     reschedule_root_alarm();
     pthread_mutex_unlock(&monitor);
     return;
   }
 
+  list_remove(alarms, alarm);
+
   alarm_callback_t callback = alarm->callback;
   void *data = alarm->data;
 
@@ -267,52 +277,37 @@ static void timer_callback(void *ptr) {
 static void reschedule_root_alarm(void) {
   assert(alarms != NULL);
 
-  bool timer_was_set = timer_set;
-  if (timer_set) {
-    timer_delete(timer);
-    timer_set = false;
-  }
+  // If used in a zeroed state, disarms the timer
+  struct itimerspec wakeup_time;
+  memset(&wakeup_time, 0, sizeof(wakeup_time));
 
-  if (list_is_empty(alarms)) {
-    bt_os_callouts->release_wake_lock(WAKE_LOCK_ID);
-    return;
-  }
+  if (list_is_empty(alarms))
+    goto done;
 
   alarm_t *next = list_front(alarms);
-  int64_t next_exp = next->deadline - now();
-  if (next_exp < TIMER_INTERVAL_FOR_WAKELOCK_IN_MS) {
-    if (!timer_was_set) {
+  int64_t next_expiration = next->deadline - now();
+  if (next_expiration < TIMER_INTERVAL_FOR_WAKELOCK_IN_MS) {
+    if (!timer_set) {
       int status = bt_os_callouts->acquire_wake_lock(WAKE_LOCK_ID);
       if (status != BT_STATUS_SUCCESS) {
         LOG_ERROR("%s unable to acquire wake lock: %d", __func__, status);
-        return;
+        goto done;
       }
     }
 
-    struct sigevent sigevent;
-    memset(&sigevent, 0, sizeof(sigevent));
-    sigevent.sigev_notify = SIGEV_THREAD;
-    sigevent.sigev_notify_function = (void (*)(union sigval))timer_callback;
-    sigevent.sigev_value.sival_ptr = next;
-    if (timer_create(CLOCK_ID, &sigevent, &timer) == -1) {
-      LOG_ERROR("%s unable to create timer: %s", __func__, strerror(errno));
-      return;
-    }
-
-    struct itimerspec wakeup_time;
-    memset(&wakeup_time, 0, sizeof(wakeup_time));
     wakeup_time.it_value.tv_sec = (next->deadline / 1000);
     wakeup_time.it_value.tv_nsec = (next->deadline % 1000) * 1000000LL;
-    if (timer_settime(timer, TIMER_ABSTIME, &wakeup_time, NULL) == -1) {
-      LOG_ERROR("%s unable to set timer: %s", __func__, strerror(errno));
-      timer_delete(timer);
-      return;
-    }
-    timer_set = true;
   } else {
-    if (!bt_os_callouts->set_wake_alarm(next_exp, true, timer_callback, next))
-      LOG_ERROR("%s unable to set wake alarm for %" PRId64 "ms.", __func__, next_exp);
+    if (!bt_os_callouts->set_wake_alarm(next_expiration, true, timer_callback, NULL))
+      LOG_ERROR("%s unable to set wake alarm for %" PRId64 "ms.", __func__, next_expiration);
+  }
 
+done:
+  timer_set = wakeup_time.it_value.tv_sec != 0 || wakeup_time.it_value.tv_nsec != 0;
+  if (!timer_set) {
     bt_os_callouts->release_wake_lock(WAKE_LOCK_ID);
   }
+
+  if (timer_settime(timer, TIMER_ABSTIME, &wakeup_time, NULL) == -1)
+    LOG_ERROR("%s unable to set timer: %s", __func__, strerror(errno));
 }