Re: Using the GNU GMP Library for Bignums in Emacs

[Paul Eggert]

Richard Stallman wrote:
> There are quite a few places in the C code of Emacs
> where execution can get stuck; that's why I added immediate quitting.
> The problems I fixed that way have all come back.

I hope they haven't come back. We tried to be methodical about preventing Emacs 
from getting stuck.

> What was the reason for this change?

Allowing immediate quitting from arbitrary points in execution causes problems 
when Emacs internals assume that actions are done in a certain order and are not 
just partly done when interrupted by a quit. 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. To do things safely now, we need to either (1) add critical sections to 
Emacs where appropriate, or (2) test the quit flag at appropriate intervals. In 
practice (2) is easier to implement and to maintain.