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Double-check next timeout when adding events

When resuming the system from a suspended state, the ev_timeout field
of a scheduled timer event may be in the past. This leads to
unexpected behavior when scheduling a short-duration timer event
immediately after returning from suspension, because the new event
does not land on top of the timeout minheap and so the event loop
(blocked on a possibly long-duration timeout) is not notified.

This patch checks for this condition and, if it obtains, notifies the
event loop.
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commit 9443868d55a829cd66a2dce24daad84c5f1ca2ed 1 parent 1367653
@flandr flandr authored
Showing with 8 additions and 2 deletions.
  1. +8 −2 event.c
10 event.c
@@ -2378,12 +2378,18 @@ event_add_nolock_(struct event *ev, const struct timeval *tv,
common_timeout_schedule(ctl, &now, ev);
} else {
+ struct event* top = NULL;
/* See if the earliest timeout is now earlier than it
* was before: if so, we will need to tell the main
- * thread to wake up earlier than it would
- * otherwise. */
+ * thread to wake up earlier than it would otherwise.
+ * We double check the timeout of the top element to
+ * handle time distortions due to system suspension.
+ */
if (min_heap_elt_is_top_(ev))
notify = 1;
+ else if ((top = min_heap_top_(&base->timeheap)) != NULL &&
+ evutil_timercmp(&top->ev_timeout, &now, <))
+ notify = 1;
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