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If time has jumped so we'd reschedule a periodic event in the past, schedule it for the future instead

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Fixes an issue reported on libevent-users in the thread "a dead
looping bug when changing system time backward". Previously, if time
jumped forward 1 hour[*] and we had a one-second periodic timer event,
that event would get invoked 3600 times.  That's almost certainly not
what anybody wants.

In a future version of Libevent, we should expose the amount of time
that the callbac kwould have been invoked somehow.

[*] Forward time jumps can happen with nonmonotonic clocks, or with
clocks that jump on suspend/resume.  It can also happen from
Libevent's point of view if the user exits from event_base_loop() and
doesn't call it again for a while.
This commit is contained in:
Nick Mathewson 2012-04-19 00:25:12 -04:00
parent bec22b4176
commit dfd808cbad
2 changed files with 31 additions and 2 deletions
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10
event.c
View File

@ -1280,9 +1280,17 @@ event_persist_closure(struct event_base *base, struct event *ev)
} else {
relative_to = now;
}
}
evutil_timeradd(&relative_to, &delay, &run_at);
if (evutil_timercmp(&run_at, &now, <)) {
/* Looks like we missed at least one invocation due to
* a clock jump, not running the event loop for a
* while, really slow callbacks, or
* something. Reschedule relative to now.
*/
evutil_timeradd(&now, &delay, &run_at);
}
run_at.tv_usec |= usec_mask;
event_add_internal(ev, &run_at, 1);
}
EVBASE_RELEASE_LOCK(base, th_base_lock);

23
test/regress.c
View File

@ -627,6 +627,27 @@ test_persistent_timeout(void)
event_del(&ev);
}
static void
test_persistent_timeout_jump(void *ptr)
{
struct basic_test_data *data = ptr;
struct event ev;
int count = 0;
struct timeval msec100 = { 0, 100 * 1000 };
struct timeval msec50 = { 0, 50 * 1000 };
event_assign(&ev, data->base, -1, EV_PERSIST, periodic_timeout_cb, &count);
event_add(&ev, &msec100);
/* Wait for a bit */
sleep(1);
event_base_loopexit(data->base, &msec50);
event_base_dispatch(data->base);
tt_int_op(count, ==, 1);
end:
event_del(&ev);
}
struct persist_active_timeout_called {
int n;
short events[16];
@ -2338,8 +2359,8 @@ struct testcase_t main_testcases[] = {
BASIC(bad_assign, TT_FORK|TT_NEED_BASE|TT_NO_LOGS),
BASIC(bad_reentrant, TT_FORK|TT_NEED_BASE|TT_NO_LOGS),
/* These are still using the old API */
LEGACY(persistent_timeout, TT_FORK|TT_NEED_BASE),
{ "persistent_timeout_jump", test_persistent_timeout_jump, TT_FORK|TT_NEED_BASE, &basic_setup, NULL },
{ "persistent_active_timeout", test_persistent_active_timeout,
TT_FORK|TT_NEED_BASE, &basic_setup, NULL },
LEGACY(priorities, TT_FORK|TT_NEED_BASE),