bug#33018: 26.1.50; thread starvation with async processes and accept-process-output

[Eli Zaretskii <eliz@gnu.org>]

> From: "Basil L. Contovounesios" <contovob@tcd.ie>
> Date: Thu, 11 Oct 2018 15:57:50 +0100
> 
> I attach a sample program test.el whose central function, test-slave,
> invokes wget asynchronously before waiting for the process to exit.
> 
> The issue I'm facing is that running test-slave twice in succession,
> each time in a new thread, causes accept-process-output to hang with no
> output (unless a timeout argument is given, in which case the function
> returns nil) the second time around.

When the hang happens, is there any wget process still alive, or did
they all exit?  Please use OS tools to find that out, don't rely on
what Emacs thinks.

> I could very well be doing or assuming something incorrectly, but what
> baffles me is that the "hang" does not occur either when Emacs is run
> non-interactively, or when "https://en.wikipedia.org/wiki/Emacs" is
> replaced with "https://www.gnu.org/software/emacs/"

Could be different properties of the servers related to async
connections, like TLS handshake or even async getaddrinfo.