[bug] Event activated by event_active on another thread may loss while event timeout

[Elylhance]

[debug] event_active: 0x9114280 (fd 19), res 4, callback 0x43f853
[debug] epoll_dispatch: epoll_wait reports 1
[debug] event_active: 0x90f0a40 (fd 10), res 2, callback 0x7f09a5fb4b20
[debug] event_del: 0x9114380 (fd 20), callback 0x43f853
[debug] timeout_process: event: 0x9114380, call 0x43f853
[debug] event_active: 0x9114380 (fd 20), res 1, callback 0x43f853
[debug] event_del: 0x9114400 (fd 21), callback 0x43f853
[debug] timeout_process: event: 0x9114400, call 0x43f853
[debug] event_active: 0x9114400 (fd 21), res 1, callback 0x43f853
[debug] event_del: 0x9114480 (fd 22), callback 0x43f853
[debug] timeout_process: event: 0x9114480, call 0x43f853
[debug] event_active: 0x9114480 (fd 22), res 1, callback 0x43f853
[debug] event_del: 0x9114280 (fd 19), callback 0x43f853
[debug] timeout_process: event: 0x9114280, call 0x43f853
[debug] event_active: 0x9114280 (fd 19), res 1, callback 0x43f853
[debug] event_process_active: event: 0x90f0a40, EV_READ   call 0x7f09a5fb4b20
[debug] event_process_active: event: 0x9114380,    call 0x43f853
[debug] event_add: event: 0x9114380 (fd 20),   EV_CLOSED EV_TIMEOUT call 0x43f853
[debug] event_add: event 0x9114380, timeout in 347343 seconds 593298 useconds, call 0x43f853
[debug] event_active: 0x9114380 (fd 20), res 4, callback 0x43f853
[debug] event_del: 0x9114380 (fd 20), callback 0x43f853
[debug] event_add: event: 0x9114380 (fd 20), EV_READ   EV_TIMEOUT call 0x43f853
[debug] event_add: event 0x9114380, timeout in 86400 seconds 0 useconds, call 0x43f853
[debug] event_active: 0x9114380 (fd 20), res 4, callback 0x43f853
[debug] event_process_active: event: 0x9114400,    call 0x43f853
[debug] event_add: event: 0x9114400 (fd 21),   EV_CLOSED EV_TIMEOUT call 0x43f853
[debug] event_add: event 0x9114400, timeout in 347343 seconds 593298 useconds, call 0x43f853
[debug] event_del: 0x9114400 (fd 21), callback 0x43f853
[debug] event_add: event: 0x9114400 (fd 21), EV_READ   EV_TIMEOUT call 0x43f853
[debug] event_add: event 0x9114400, timeout in 86400 seconds 0 useconds, call 0x43f853
[debug] event_process_active: event: 0x9114480,    call 0x43f853
[debug] event_add: event: 0x9114480 (fd 22),   EV_CLOSED EV_TIMEOUT call 0x43f853
[debug] event_add: event 0x9114480, timeout in 347343 seconds 593298 useconds, call 0x43f853
[debug] event_del: 0x9114480 (fd 22), callback 0x43f853
[debug] event_add: event: 0x9114480 (fd 22), EV_READ   EV_TIMEOUT call 0x43f853
[debug] event_add: event 0x9114480, timeout in 86400 seconds 0 useconds, call 0x43f853
[debug] event_process_active: event: 0x9114280,    call 0x43f853
[debug] event_add: event: 0x9114280 (fd 19),   EV_CLOSED EV_TIMEOUT call 0x43f853
[debug] event_add: event 0x9114280, timeout in 347343 seconds 593298 useconds, call 0x43f853
[debug] event_del: 0x9114280 (fd 19), callback 0x43f853
[debug] event_add: event: 0x9114280 (fd 19), EV_READ   EV_TIMEOUT call 0x43f853
[debug] event_add: event 0x9114280, timeout in 86400 seconds 0 useconds, call 0x43f853
--------------------------------------------------------------------------------------

the EV_WRITE event activated by event_active() on 0x9114280 loss

[Elylhance]

/* Activate every event whose timeout has elapsed. */
static void
timeout_process(struct event_base *base)
{
	/* Caller must hold lock. */
	struct timeval now;
	struct event *ev;

	if (min_heap_empty_(&base->timeheap)) {
		return;
	}

	gettime(base, &now);

	while ((ev = min_heap_top_(&base->timeheap))) {
		if (evutil_timercmp(&ev->ev_timeout, &now, >))
			break;

		/* delete this event from the I/O queues */
		event_del_nolock_(ev, EVENT_DEL_NOBLOCK);          //<-- this line removed all active events

		event_debug(("timeout_process: event: %p, call %p",
			 ev, ev->ev_callback));
		event_active_nolock_(ev, EV_TIMEOUT, 1);
	}
}

[0xdddddddd]

/* Activate every event whose timeout has elapsed. */
static void
timeout_process(struct event_base *base)
{
	/* Caller must hold lock. */
	struct timeval now;
	struct event *ev;

	if (min_heap_empty_(&base->timeheap)) {
		return;
	}

	gettime(base, &now);

	while ((ev = min_heap_top_(&base->timeheap))) {
		if (evutil_timercmp(&ev->ev_timeout, &now, >))
			break;

		/* delete this event from the I/O queues */
		event_del_nolock_(ev, EVENT_DEL_NOBLOCK);          //<-- this line removed all active events

		event_debug(("timeout_process: event: %p, call %p",
			 ev, ev->ev_callback));
		event_active_nolock_(ev, EV_TIMEOUT, 1);
	}
}

If a timer is initialized, calling event_assign event_add two times in a row will cause the timer to expire!
will get stuck at the reference code

[azat]

timeout_process works under lock, so any modifications to the event should be locked.

Have you enabled threads for event_base? evthread_use_pthreads

[Elylhance]

yes. I call evthread_use_pthreads in the main thread first, then new event_base in worker threads.