tevent: optimize adding new timer events

As new timestamps typically get higher:-)
it's better to traverse the existing list from
the tail.

This is not completely optimal, but it should be better
than before.

A second optimization could be done for zero timestamps,
we would just remember the last_zero_timer,
but that would change the internal ABI.
Normally thatshould not be a poblem, but the Samba's
source3/lib/events.c abuses tevent_internal.h
from the current source tree, even if an external tevent.h
is used. The other problem is that it makes use of
tevent_common_add_timer() without using
tevent_common_loop_timer_delay().

Signed-off-by: Stefan Metzmacher <metze@samba.org>

diff --git a/lib/tevent/tevent_timed.c b/lib/tevent/tevent_timed.c
index d3ec8f5913e2dcc9f42501a0c97526fdd5b7002a..fd954f42d834cab3bc123c63e9972eeb9d6bd1ba 100644 (file)
--- a/lib/tevent/tevent_timed.c
+++ b/lib/tevent/tevent_timed.c
@@ -160,7 +160,7 @@ struct tevent_timer *tevent_common_add_timer(struct tevent_context *ev, TALLOC_C
                                             const char *handler_name,
                                             const char *location)
 {
-       struct tevent_timer *te, *last_te, *cur_te;
+       struct tevent_timer *te, *prev_te, *cur_te;
 
        te = talloc(mem_ctx?mem_ctx:ev, struct tevent_timer);
        if (te == NULL) return NULL;
@@ -174,17 +174,33 @@ struct tevent_timer *tevent_common_add_timer(struct tevent_context *ev, TALLOC_C
        te->additional_data     = NULL;
 
        /* keep the list ordered */
-       last_te = NULL;
-       for (cur_te = ev->timer_events; cur_te; cur_te = cur_te->next) {
-               /* if the new event comes before the current one break */
-               if (tevent_timeval_compare(&te->next_event, &cur_te->next_event) < 0) {
-                       break;
+       prev_te = NULL;
+       /*
+        * we traverse the list from the tail
+        * because it's much more likely that
+        * timers are added at the end of the list
+        */
+       for (cur_te = DLIST_TAIL(ev->timer_events);
+            cur_te != NULL;
+            cur_te = DLIST_PREV(cur_te))
+       {
+               int ret;
+
+               /*
+                * if the new event comes before the current
+                * we continue searching
+                */
+               ret = tevent_timeval_compare(&te->next_event,
+                                            &cur_te->next_event);
+               if (ret < 0) {
+                       continue;
                }
 
-               last_te = cur_te;
+               break;
        }
+       prev_te = cur_te;
 
-       DLIST_ADD_AFTER(ev->timer_events, te, last_te);
+       DLIST_ADD_AFTER(ev->timer_events, te, prev_te);
 
        talloc_set_destructor(te, tevent_common_timed_destructor);