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Re: Using the GNU GMP Library for Bignums in Emacs

From: Paul Eggert
Subject: Re: Using the GNU GMP Library for Bignums in Emacs
Date: Mon, 23 Apr 2018 21:34:58 -0700
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.7.0

Richard Stallman wrote:

   > In the old days we could assume that execution order at the
   > machine level was the same order as in the C program source code,
   > which meant that as long as the C source code did things in the
   > right order Emacs could survive immediate quitting. That
   > assumption is no longer true.

That problem exists in theory.  Did the problem actually occur?

As Eli wrote, we did make the change in response to a bug report. I do not recall all the details offhand. The theory is pretty clear, though.
If (2) means to check for quitting as needed in each and every place
code where immediate_quit was formerly used, that would thoroughly do
the job, but did we handle all of those places?

We attempted to check for quitting at every place where a check is needed to avoid unbounded or too-long computation, and I recall using the immediate_quits in the old code as a cue for where to check for quitting in the new code. We tried to be conservative about this, and as I recall we put in some checks even when we weren't sure they were needed. Perhaps we missed some places, but if so we can fix them as problems arise (and in this sense the new method is similar to the old one).

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