Re: accept-process-output throws

[Eli Zaretskii <eliz@gnu.org>]

> From: JD Smith <jdtsmith@gmail.com>
> Date: Wed, 24 Nov 2021 00:14:06 -0500
> Cc: emacs-devel@gnu.org
> 
> 
> 
> > On Nov 23, 2021, at 10:25 PM, Eli Zaretskii <eliz@gnu.org> wrote:
> > 
> > Is this in "emacs -Q"?  If so, how did you start the process, and what
> > do you have in the process-filter and process-sentinel functions for
> > this process?
> 
> This is in a customized inferior python mode (a comint-derived mode), running iPython as the process.   I discovered the issue with `python-shell-send-string-no-output', which adds its own pre-output-filter to accumulate and discard process output.  The no-output commands are being sent to the process from a post-command hook which kicks off a timer (to gather completion and syntax data).  The command results arrive promptly, but when the non-local exit occurs, they “escape" the pre-output filtering and show up in the buffer.  When this occurs, it is always as a result of the non-local exit of `accept-process-output’.  I’ve found the problem gets more severe when the PCH-launched timer's delay is very small (<0.1s), i.e. when commands are sent in quick succession while typing.
> 
> I do not have an emacs -Q demo of this but can look at creating one with the stock python-shell-mode.  In the meantime I’ve found that if I bind (inhibit-quit t), remove `with-local-quit' and specify a timeout in `accept-process-output' (to silence the warning about the blocking call), this entirely prevents the non-local exit.  But this I feel is more of a workaround than a solution, and I still do not understand the original problem.

In this kind of complicated situations, I usually find it much simpler
and more efficient to run under GDB with a breakpoint on Fsignal and
Fthrow.  Then, when one of these breaks, examine the backtrace to find
out which code exited non-locally.