From: zedshaw@...
Date: 2005-09-09T00:41:05+09:00
Subject: Re: myriad/event comment (was RE: [ANN] Rio 0.3.4)

...

> I second this sentiment,  I saw the announcement of myriad/ruby_event
> yesterday and decided to recreate my chatserver which uses a select
> loop with the orc_server.rb example as the basis. Took a couple of
> hours and works a lot better than my home grown effort:)
>
That's really cool.  The OneRoomChat was mostly an example of how vrec
works as a means of passing messages instead of line-endings.  If I were
to do orc as a *real* chat thing, I'd probably ditch the one vrec per
message param and go with a single vrec per message containing something
like YAML commands or simple shellwords commands.  Oh, and also make it do
more than one room. :-)

> one question regarding database access. twisted has some kind of
> threaded pool of database connections that doesn't let it block or at
> least minimises blocking, what's the best way to accomplish this in
> myriad/ruby_Event.
>

Well, there's three ways to answer this depending on what you need:

1.  You need to just access a DB without blocking all the other libevent
stuff.  This is going to be really hard without some form of native
threading or a pure Ruby DB interface.  Most of the DB api's are blocking,
so you've got to wrap the call with some kind of threading.  I'm also
pretty sure that, even if the DB supports async queries, the Ruby DBI
doesn't (CMIIW).  If the Ruby DB support is native Ruby, then the simplest
solution is to create your own pseudo-async query mechanism running in a
Ruby thread.  This second option is complicated with stuff like having to
create a timer to periodically make Ruby run, etc.  I may look at
something to support registering a Ruby thread with libevent for
operations like this.  Take a look at the Myriad.timeout function.  You
can do stuff like this:

timeout = Myriad.timeout(2,0) do
  puts "2 SECONDS!"
  timeout.enable
end

And myriad will loop the block every 2 seconds without blocking libevent.

2.  You want a database framework written in Myriad.  Remember how you
said Twisted was complicated?  I wonder why Twisted would be so
complicated.  Hmmmm.  Maybe it's because they have too much in it? 
Seriously though, if someone was really interested in doing this then
that'd be cool, but I'd make it a separate project.  I like things being
nice, small, discrete and orthogonal.

3.  Your question really has nothing really to do with DBs and more to do
with running non-Myriad stuff without blocking Myriad.  You've got
basically the same problem as with the DB:  either you need a native
thread, a ruby thread, or you need to invert who's in control (i.e. say
the GTK event loop rather than libevent loop).  See above for the native
thread and ruby thread possibilities.  The Myriad.timeout will really help
with this.  To invert the loop, you need to dip into the base Event module
with:

  Event.init(10)
  # do you myriad configs like normal here

Then somewhere in the other event loop (like GTK's) during it's "idle"
phase  you do:

  Event.loop(Event::NONBLOCK)

To get Myriad to go once without blocking (actually libevent, but same
difference).

Anyway, that's the long winded answer.  The short answer is I'll look at
Ruby Threads and Myriad integration which might solve some of the
problems.

Zed A. Shaw
http://www.zedshaw.com/