In 11b8bbe one thing that was claimed was that we now properly set the
Notifier's actual fd on the NotifierActivationEvent. It turns out that
claim was false because a crucial step was forgotten: actually set the
m_notifier_fd when registering. Despite that mistake, it ultimately was
irrelevant as the methods on NotifierActivationEvent are currently
unused code. We were posting the event to the correct Notifier receiver
so the on_activation was still getting invoked.
Given they are unused, NotifierActivationEvent can be defined the same
way as TimerEvent is, where we just pass the event type enum to the
Event base class. Additionally, NotificationType can be moved to
the Notifier header as this enum is now always used in the context of
creating or using a Notifier instance.
Timers scheduled with identical `fire_time` could fire out of order
because the heap is not stable. This change assigns a monotonically
increasing `sequence_id` when a timer is scheduled and extend the heap
comparator to order by (`fire_time`, `sequence_id`). This guarantees
FIFO among timers with the same deadline.
This matches the HTML "run steps after a timeout" ordering requirement:
older invocations with <= delay complete before newer ones.
https://html.spec.whatwg.org/multipage/timers-and-user-prompts.html#run-steps-after-a-timeout
The issue with that refactor was that the same fd can be used in more
than one notifier. This reverts us back to using 2 members to track the
notifiers in play.
POLLHUP is set when the remote end of the monitored fd is closed. There
may still be some buffered data to read from the socket, however. Some
systems do not set POLLIN in these cases. So we should just always try
to read from fds when we receive this event.
