Thank you for the clarification. I have now read the original explanation,
and it makes sense.  Ultimately, I think the sit-for is the right approach
for my wait-for-any-process-or-input problem.  Am I right to assume  it's
not affected by your explanation, and that I can expect immediate return
there?

If so, there's some unfortunate combination of factors that cause a
hard-to-reproduce hang in Emacs, at least in the packages where I use it.
But that's a matter for a future issue...

Thanks,
João

On Mon, Oct 8, 2018, 21:25 Eli Zaretskii <eliz@gnu.org> wrote:

> > From: João Távora <joaotavora@gmail.com>
> > Date: Mon, 8 Oct 2018 21:06:12 +0100
> > Cc: 32986@debbugs.gnu.org
> >
> > I will fully read and process your thorough reply later tonight or
> tomorrow, but in the meantime let me just
> > restate, or clarify in case it wasn't clear, that I expect the 30s, 15s
> and 0.1s case to break equally as quickly,
> > namely as quick as I can type the first input.
> >
> > And indeed that's what happens on Linux and Mac OSX, but not on
> Windows.  If your reply already addresses
> > this apparent discrepancy, then I apologize for my premature
> clarification in advance.
>
> I didn't investigate the difference in behavior between Windows and
> GNU/Linux, because I see similar behavior on both systems if I
> neutralize all the "contaminating" factors which I described.  It is
> possible that it's easier to get the 30-sec delay on Windows because
> keyboard input works without signals there, and uses messaging between
> 2 threads running within the Emacs process.
>
> In any case, my point is that your expectation for immediate return is
> incorrect, and I tried to explain why.
>