sam.saffron / gmail.com wrote:
> Hmmm, what about just bringing in the IO Manager APIs
> including Ruby helpers prior to re-introducing the green
> threads? 

One big problem I notice with existing IO manager APIs
(libev/libevent/EventMachine) is multi-threading was as an
afterthought to them.  As in, throw a lock around a
single-threaded event loop and call it a day.

Ruby was this way, too; but want to work towards changing that
and embracing the multi-thread friendliness baked into APIs
provided by kqueue and epoll.

Btw, some of the discussion/planning around this started in:
https://public-inbox.org/ruby-core/20170402023514.GB30476@dcvr/t/

> As it stands kqueue/epoll abstractions always require another
> fat dependency and there is no official API to consume them.

I don't know if exposing a new API around them is desirable.
For human-friendliness, it seems desirable to keep the Ruby API
synchronous even if internal bits become async.

I think it's also desirable to be able to change some/most
existing Thread uses to auto-Fiber/Threadlet/Thriber without
having to re-design things, just changing "Thread.new" to
something else.

> Even just solving this problem is enough of a hornets nest
> prior to introduction of other complications.
> 
> epoll is notoriously monstrous,
> http://cvs.schmorp.de/libev/ev_epoll.c?view=markup so having
> an officially supported abstraction would be a great start.

I disagree.  IMHO, Lehman's notes and complaints against epoll
are either out-of-date or his mental model went wrong somewhere.
Fwiw, fs/eventpoll.c is straightforward and easy-to-understand in
git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git

> Wouldn't having these abstractions allow building this by hand
> using existing Fiber?

One question is, how painful will it be in Ruby?

I've kinda soured on _nonblock APIs in Ruby over the years.  For
example, in https://bugs.ruby-lang.org/issues/14404 I don't
think there's a non-painful Ruby way to resume a partial writev.
Doable, of course, but it requires extra allocations and copies.
Resuming a partial write_nonblock today without writev isn't great,
either...

With a synchronous interface (IO#write), dealing with partial
writev in C is only a few adds/subracts; and we wont expose
pointer arithmetic in Ruby :)

And then there's also stuff like IO.copy_stream not having
a _nonblock analogue...

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