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Message-ID: <3E31D637.1030306@kegel.com>
Date: Fri, 24 Jan 2003 16:11:35 -0800
From: Dan Kegel <dank@kegel.com>
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To: "Randy.Dunlap" <rddunlap@osdl.org>
CC: Matti Aarnio <matti.aarnio@zmailer.org>, Corey Minyard <minyard@acm.org>,
       Mark Mielke <mark@mark.mielke.cc>, Mark Hahn <hahn@physics.mcmaster.ca>,
       linux-kernel@vger.kernel.org
Subject: Re: debate on 700 threads vs asynchronous code
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Randy.Dunlap wrote:
> On Sat, 25 Jan 2003, Matti Aarnio wrote:
> 
> | On Fri, Jan 24, 2003 at 04:53:46PM -0600, Corey Minyard wrote:
> | ...
> | > I would disagree.  One thread per connection is easier to conceptually
> | > understand.  In my experience, an event-driven model (which is what you
> | > end up with if you use one or a few threads) is actually easier to
> | > correctly implement and it tends to make your code more modular and
> | > portable.
> |
> |   An old thing from early annals of computer science (I browsed Knuth's
> | "The Art" again..) is called   Coroutine.
> |
> | Gives you "one thread per connection" programming model, but without
> | actual multiple scheduling threads in the kernel side.  ...
> | Doing coroutine library all in portable C (by means of setjmp()/longjmp())
> | is possible, but not very efficient.  A bit of assembly helps a lot.

There's also an elegant implementation that uses switch statements
or computed gotos; see http://www.chiark.greenend.org.uk/~sgtatham/coroutines.html
I'm using it.  It's a bit limited, but hey, it works for me.

> Davide Libenzi (epoll) likes and discusses coroutines on one of his
> web pages:  http://www.xmailserver.org/linux-patches/nio-improve.html
> (search for /coroutine/)

IMHO coroutines are harder to use than either threads or nonblocking I/O.
Then again, I don't like Scheme; many things in this world are a matter of taste.
- Dan

-- 
Dan Kegel
http://www.kegel.com
http://counter.li.org/cgi-bin/runscript/display-person.cgi?user=78045

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