bug#44007: 26.3; Strange shell mode performance

[Eli Zaretskii]

> From: Herman, Géza <geza.herman@gmail.com>
> Cc: Herman Géza <geza.herman@gmail.com>,
>  44007@debbugs.gnu.org
> Date: Mon, 06 Nov 2023 14:37:52 +0100
> 
> 
> I think it is a bug because Emacs doesn't try to read again if one 
> read() was successful.

I believe reading again immediately could make Emacs unresponsive for
prolonged periods of time.  We are talking about reading sub-process
output asynchronously, which means we must not read in a tight loop,
because that would have the same effect as calling a subprocess
synchronously and waiting for it to finish.

Even in this particular scenario, the user should be able to switch to
another buffer and issue commands, while Emacs is reading from the
shell or some program invoked from the shell.