Date: 05 Nov 1999 16:00:34 +0000 From: Randell Jesup <rjesup@wgate.com> To: arch@freebsd.org Subject: Re: FSM's Message-ID: <ybuhfj1orml.fsf_-_@jesup.eng.tvol.net.jesup.eng.tvol.net> In-Reply-To: "Pedro Fernando Giffuni"'s message of "Fri, 05 Nov 1999 10:18:52 -0500" References: <Pine.BSF.4.10.9911041810260.50464-100000@hub.freebsd.org> <3822F55C.506F5E48@bachue.usc.unal.edu.co>
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Peter Jeremy <jeremyp@gsmx07.alcatel.com.au> writes:
>>1) A means of allowing programmers to build procedural
>> soloutions instead of state machines.
>>
>> This is really a programmer convenience, for programmers
>> who know how to write linear code, but don't know how to
>> do finite state automata,
>
>I think that's being a bit unfair.
>
>One problem with FSA's is that following their internal logic can
>sometimes be substantially more difficult than following an equivalent
>linear control flow. This makes than more difficult to write and
>check - and increases the maintenance costs.
FSM's also have the implicit assumption that inputs can be handled
in order of reception, and in a timely fashion. If some inputs need
quicker responses than the time to handle other inputs allows, FSM's have
a problem. This is one reason why threaded programs/OS's can have a very
snappy UI response 'feel' compared to single-threaded - the UI response
can run on a different thread than handling of the UI-invoked events.
This isn't even considering the issues of (long) blocking system calls,
which make it more of an issue.
FSM's where there are a number of loosely related sets of states
can be very confusing as well. Threads mean you have to worry about
synchronization and locking. Oh well; every technique has plusses and
minuses.
>>1) SMP scalability
>
>IMHO, this is going to rise in importance over time - and probably
>become the predominant reason for writing threaded code. It's
>becoming more and more difficult to make single processors faster,
>so fast machines will increasingly rely on multiple processors.
This hasn't happened yet, though it's been predicted for a
decade or more - but I agree, it has to happen eventually.
--
Randell Jesup, Worldgate Communications, ex-Scala, ex-Amiga OS team ('88-94)
rjesup@wgate.com
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