Allow faster eventhandler dispatching by keeping pointers to handler lists.

[Matt Joras]

On 10/30/2017 09:05, Ian Lepore wrote:
> On Mon, 2017-10-30 at 09:17 +0100, Hans Petter Selasky wrote:
>> On 10/29/17 18:03, Ian Lepore wrote:
>>> Oh.  Right.  Hmmm, I think malloc() is required to support the case
>>> where a handler registers before the static list init is invoked, and I
>>> do think that's a useful feature to preserve.  That means the lists
>>> aren't really static, though, which then makes STATIC a bit out of
>>> place in the new function/macro names.
>> Why not use RCU here, and then update sys/queue.h to be RCU safe?
>>
>> --HPS
> I'm not sure how that suggestion relates to that paragraph, but the
> code already does use a form of RCU to handle deletion of registered
> handlers from individual event lists.  It could probably benefit from a
> rewrite to more fully embrace RCU and use it for insertions as well,
> but that's beyond the scope of these changes, which are trying to
> eliminate the worst uses of a global lock at a higher level than
> maintaining the list for a single event.
>
> -- Ian

Agreed. There are all sorts of clever things we can do with a more
comprehensive rewrite. It would be a nice place to try out RCU-ish
methods of handling object removal without locks.

Matt