From: Vidar Hokstad <vidar.hokstad@...>
Date: 2006-11-05T19:10:14+09:00
Subject: Re: Nonblocking IO read


ara.t.howard@noaa.gov wrote:
> On Wed, 1 Nov 2006 srobertjames@gmail.com wrote:
>
> > How can I perform a nonblocking IO read?  That is, read whatever is
> > there to read and return.  If there's nothing yet, just return.
> >
> > Failing that, is there a way to manually check if there's anything to
> > read or the read will block?
> >
> > (Note that I'm developing for both 'nix and Windows.)
>
> it can't be done.  search the archives, this sort of thing almost always
> indicates a design flaw.  for instance - what will your program do if there is
> no input?

I have a messaging middleware server running right now that is
processing millions of messages a day. It's written in Ruby, and does
_all_ it's work in a single thread using IO multiplexing with select().


Not only can it be done - it is fairly easy (~700 lines for the entire
app, including db persistence support etc.). Doing the same thing with
threads and blocking IO, on the other hand, would fall apart horribly
due to the way Ruby does threading. Forking also wouldn't be an option
as the processes would still need to actually exchange those messages.

In fact, internally, Ruby does all it's IO using non-blocking IO
exactly because the threading model would cause everything to block
otherwise. Incidentally that's also one of the reasons why using
threads + blocking IO performs extremely badly in Ruby once the number
of threads gets beyond a certain level, because it causes Ruby to call
select() far too often.

Vidar