Motivation:
Since forever we had a major bug in the Selector: In this condition:
- kqueue/epoll had many events
- in one of the earlier events we unregister a Channel whose fd is on of
the later events
- we subsequently (still in the same event loop tick) register a new
channel which gets the same fd as the previously closed one
then we would deliver an event that was meant for a previous channel to
a newly opened one.
Thanks to @mcdappdev for hitting this bug, helping us debug it and also
providing a repeatedly working repro.
Modifications:
if during event delivery any fd gets unregistered, we stop delivering
the remaining events and rely on the selector to redeliver them
again next time.
Result:
we don't deliver events for previously closed channels to new ones.