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From: jack@piring.cwi.nl (Jack Jansen)
Newsgroups: comp.unix.wizards
Subject: Re: Re^2: What kinds of things would you want in the GNU OS?
Message-ID: <8318@boring.cwi.nl>
Date: 8 Aug 89 08:53:14 GMT
References: <160@uucs1.UUCP> <8311@boring.cwi.nl> <5568@ficc.uu.net>
Sender: news@cwi.nl
Organization: AMOEBA project, CWI, Amsterdam
Lines: 48

In article <5568@ficc.uu.net> peter@ficc.uu.net (Peter da Silva) writes:
>[ gaf@uucs1.UUCP (gaf) wants an n-way wait() ]
>
>In article <8311@boring.cwi.nl>, guido@piring.cwi.nl (Guido van Rossum) writes:
>> Sounds like you need multiple threads in a single address space, or
>> light-weight threads as they are referred to in a discussion of the
>> subject in neighboring newsgroups.  I agree that they are *very* nice to
>> have in an OS.
>
>An n-way wait can be implemented by using N threads, having each of them
>waiting on a seperate event, and having a thread signal the mainline
>when its event occurs. It can also be implemented using software interrupts...
>(or in UNIX terms, signals). It's usually desirable, though, to implement
>an n-way wait anyway, because it may be more efficient.


Well, I've noticed that it is actually the other way around: everytime
I use select() I really wanted multiple threads in the first place
and only used select because they weren't there.

Usually, my select code looks like

    while(1) {
	select()
	if( event-1 ) {
	    handle-event-1;
	}
	if( event-2 ) {
	    handle-event-2;
	}
	etc;
    }
With multiple threads, you would have multiple threads each doing
a simple
	while(1) {
	    wait();
	    do-event;
	}
Not only do I find this much easier to understand, but there are also
other advantages, like having local state on the stack in stead of
having a global array that you have to index by event number each time
(think of things like handling two or more keyboards at the same
time).
-- 
--
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