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Re: threads and kill-buffer

From: Tom Tromey
Subject: Re: threads and kill-buffer
Date: Wed, 05 Sep 2012 19:53:23 -0600
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/24.2 (gnu/linux)

Tom> No, it really is impossible in the context of Emacs, even with
Tom> preemptive threads.  The impossibility lies in the "GCd and reallocated"
Tom> step.  If thread A has a handle on the buffer, then it cannot be GCd.

Stephen> Ah you're right.  ... but subtract GC, and just have the buffer
Stephen> reallocated in thread B, and guess what happens?[1]

Subtracting GC doesn't make sense, since we're only talking about Emacs

Stephen> So I didn't get it right, and you miss things, too.

Sure, I do, but not this:

Stephen> Footnotes: 
Stephen> [1]  enlarge_buffer_text() @ buffer.c, ~l.4819.

Things like this are why the threading implementation is cooperative.

But actually, even that is too strong.  I think the implementation only
has to be cooperative as far as the C code in Emacs is concerned; and
that it can appear to be preemptive from the Lisp VM perspective.  Task
switching during I/O is a step in that direction.

Full preemption at the C level is a harder proposition.  I don't intend
to work on that.


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