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Re: What's the problem? (Was: Are there plans for a multi-threaded Emacs

From: David Kastrup
Subject: Re: What's the problem? (Was: Are there plans for a multi-threaded Emacs?)
Date: 10 Dec 2003 02:41:22 +0100
User-agent: Gnus/5.09 (Gnus v5.9.0) Emacs/21.3.50

Stefan Monnier <address@hidden> writes:

> > Do you have an idea what figure we are speaking about here?  I
> > repeat: _every_ access to a symbol that now works directly instead
> > has to work via stack pointers.  And CPUs like the x86 do not have
> > spare address registers flying around.
> I wouldn't worry too much about speed: there's lots of room for
> optimization in the interpreter.  The problem I see is one of
> semantics because looking up bindings in the stack doesn't seem to
> work so great when you take into account interaction with
> buffer-local variables.  That is: it tends to give you subtly
> different semantics than the current one.

Actually, considering the warnings in the manual about the necessary
orders of exception-catchers and buffer switches and let and similar,
I would expect that the different semantics would in most cases be
rather an advantage (and what the programmer would have expected
naively in the first place).  A basically static variable allocation
that gets saved and restored on a stack is more prone to surprising
side effects than a straightforward stack.

David Kastrup, Kriemhildstr. 15, 44793 Bochum

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