Simplify alarm API.

This change removes a corner case that needs to be handled (what happens if you
add an alarm twice?). This corner case was never used, nor tested.
	Change on 2014/12/15 by ctiller <ctiller@google.com>
-------------
Created by MOE: http://code.google.com/p/moe-java
MOE_MIGRATED_REVID=82168179

src/core/channel/client_setup.c

@@ -212,11 +212,11 @@ void grpc_client_setup_request_finish(grpc_client_setup_request *r,
     /* TODO(klempner): Replace these values with further consideration. 2x is
        probably too aggressive of a backoff. */
     gpr_timespec max_backoff = gpr_time_from_minutes(2);
+    gpr_timespec deadline =
+        gpr_time_add(s->current_backoff_interval, gpr_now());
     GPR_ASSERT(!s->in_alarm);
     s->in_alarm = 1;
-    grpc_alarm_init(&s->backoff_alarm, backoff_alarm_done, s);
-    grpc_alarm_add(&s->backoff_alarm,
-                   gpr_time_add(s->current_backoff_interval, gpr_now()));
+    grpc_alarm_init(&s->backoff_alarm, deadline, backoff_alarm_done, s);
     s->current_backoff_interval =
         gpr_time_add(s->current_backoff_interval, s->current_backoff_interval);
     if (gpr_time_cmp(s->current_backoff_interval, max_backoff) > 0) {

src/core/iomgr/alarm.h

@@ -50,9 +50,10 @@ typedef struct grpc_alarm grpc_alarm;
    canceled (CANCELLED). alarm_cb is guaranteed to be called exactly once,
    and application code should check the status to determine how it was
    invoked. The application callback is also responsible for maintaining
-   information about when to free up any user-level state.  */
-void grpc_alarm_init(grpc_alarm *alarm, grpc_iomgr_cb_func alarm_cb,
-                     void *alarm_cb_arg);
+   information about when to free up any user-level state.
+   Returns 1 on success, 0 on failure. */
+int grpc_alarm_init(grpc_alarm *alarm, gpr_timespec deadline,
+                    grpc_iomgr_cb_func alarm_cb, void *alarm_cb_arg);
 
 /* Note that there is no alarm destroy function. This is because the
    alarm is a one-time occurrence with a guarantee that the callback will
@@ -62,12 +63,6 @@ void grpc_alarm_init(grpc_alarm *alarm, grpc_iomgr_cb_func alarm_cb,
    the alarm, the user is responsible for determining when it is safe to
    destroy that state. */
 
-/* Schedule *alarm to expire at deadline. If *alarm is
-   re-added before expiration, the *delay is simply reset to the new value.
-   Return GRPC_EM_OK on success, or GRPC_EM_ERROR on failure.
-   Upon failure, caller should abort further operations on *alarm */
-int grpc_alarm_add(grpc_alarm *alarm, gpr_timespec deadline);
-
 /* Cancel an *alarm.
    There are three cases:
    1. We normally cancel the alarm

src/core/iomgr/iomgr_libevent.c

@@ -361,29 +361,18 @@ static void libevent_alarm_cb(int fd, short what, void *arg /*=alarm*/) {
   }
 }
 
-void grpc_alarm_init(grpc_alarm *alarm, grpc_iomgr_cb_func alarm_cb,
-                     void *alarm_cb_arg) {
+int grpc_alarm_init(grpc_alarm *alarm, gpr_timespec deadline,
+                    grpc_iomgr_cb_func alarm_cb, void *alarm_cb_arg) {
   grpc_libevent_activation_data *adata =
       &alarm->task.activation[GRPC_EM_TA_ONLY];
+  gpr_timespec delay_timespec = gpr_time_sub(deadline, gpr_now());
+  struct timeval delay = gpr_timeval_from_timespec(delay_timespec);
   alarm->task.type = GRPC_EM_TASK_ALARM;
   gpr_atm_rel_store(&alarm->triggered, ALARM_TRIGGER_INIT);
   adata->cb = alarm_cb;
   adata->arg = alarm_cb_arg;
   adata->prev = NULL;
   adata->next = NULL;
-  adata->ev = NULL;
-}
-
-int grpc_alarm_add(grpc_alarm *alarm, gpr_timespec deadline) {
-  grpc_libevent_activation_data *adata =
-      &alarm->task.activation[GRPC_EM_TA_ONLY];
-  gpr_timespec delay_timespec = gpr_time_sub(deadline, gpr_now());
-  struct timeval delay = gpr_timeval_from_timespec(delay_timespec);
-  if (adata->ev) {
-    event_free(adata->ev);
-    gpr_log(GPR_INFO, "Adding an alarm that already has an event.");
-    adata->ev = NULL;
-  }
   adata->ev = evtimer_new(g_event_base, libevent_alarm_cb, alarm);
   /* Set the trigger field to untriggered. Do this as the last store since
      it is a release of previous stores. */

src/core/surface/call.c

@@ -868,6 +868,5 @@ void grpc_call_set_deadline(grpc_call_element *elem, gpr_timespec deadline) {
   }
   grpc_call_internal_ref(call);
   call->have_alarm = 1;
-  grpc_alarm_init(&call->alarm, call_alarm, call);
-  grpc_alarm_add(&call->alarm, deadline);
+  grpc_alarm_init(&call->alarm, deadline, call_alarm, call);
 }

test/core/iomgr/alarm_test.c

@@ -116,8 +116,7 @@ static void test_grpc_alarm() {
   gpr_cv_init(&arg.cv);
   gpr_event_init(&arg.fcb_arg);
 
-  grpc_alarm_init(&alarm, alarm_cb, &arg);
-  grpc_alarm_add(&alarm, gpr_time_add(tv0, gpr_now()));
+  grpc_alarm_init(&alarm, gpr_time_add(tv0, gpr_now()), alarm_cb, &arg);
 
   alarm_deadline = gpr_time_add(gpr_now(), tv1);
   gpr_mu_lock(&arg.mu);
@@ -162,8 +161,8 @@ static void test_grpc_alarm() {
   gpr_cv_init(&arg2.cv);
   gpr_event_init(&arg2.fcb_arg);
 
-  grpc_alarm_init(&alarm_to_cancel, alarm_cb, &arg2);
-  grpc_alarm_add(&alarm_to_cancel, gpr_time_add(tv2, gpr_now()));
+  grpc_alarm_init(&alarm_to_cancel, gpr_time_add(tv2, gpr_now()), alarm_cb,
+                  &arg2);
   grpc_alarm_cancel(&alarm_to_cancel);
 
   alarm_deadline = gpr_time_add(gpr_now(), tv1);