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Re: What are the arguments in favor of delay/force in eval.c?

From: Rob Browning
Subject: Re: What are the arguments in favor of delay/force in eval.c?
Date: Wed, 07 Dec 2005 16:52:30 -0800
User-agent: Gnus/5.110004 (No Gnus v0.4) Emacs/21.4 (gnu/linux)

Kevin Ryde <address@hidden> writes:

> An even more radical idea would be not to have a mutex at all.  If
> two threads are simultaneously forcing then whichever finishes first
> sets the forced value.  (The same way that recursive forcing results
> in the first finisher setting the value.)

This would only work if you forbid side-effects, right?  Either that,
or perhaps we'd just have to document the resulting semantics,
whatever they are.

I was also wondering about the possibilities for deadlock with the
current code, and then what they might be with a srfi-45 force, which
may do more work (it's basically a trampoline approach to the problem
described in the srfi).

I suppose one of the questions here (and one of the traditional
questions) is just how much protection/overhead Guile should try to
provide by default.

> (Oh, and to bring this slightly back on-topic, I'm imagining that if
> streams or lazy stuff throw off quite a few forced promises then it's
> a good thing for them to be small and fast.)

Quite possibly.  

Rob Browning
rlb and; previously
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