bug#11724: 24.1; emacs freeze (full hang, ctrl+G or kill -15 do not help) on rope lucky assist

[Stefan Monnier]

>> Yes, I pretty well understand that point. 
>> But why Emacs 24 hangs completely without reacting
>> to C-g and other keys?

Because there are situations where Emacs temporarily inhibits C-g.
These are situations where using accept-process-output without a timeout
is fundamentally a bug (it currently doesn't signal an error in those
cases, but it does output a warning message).

>> I consider *this* to be emacs bug because it makes it impossible for
>> me to debug the problem on Lisp level to properly report it to
>> package maintainers as you suggest. 

In Emacs-24, you can set `debug-on-event' to `sigusr1' after which
sending a SIGUSR1 signal to the process will put you in the
Elisp debugger.

> until there is some output. It doesn't mention quitting being
> inhibited though. By experiment, it is not:

Quit is inhibitted while running pre/post-command-hook, timers, process
filters and sentinels, jit-lock, and probably a few more similar cases.

The general rule is that it's inhibited when running code "behind the
back of the user", so that the user won't accidentally interrupt that
code if she hits C-g for some other reason (e.g. to get out of
a minibuffer).


        Stefan