Tags: patch


**Present context:**

I'm running into an issue in emacs-syncthing [1] where making a few
localhost network requests are taking a full second (blocking Emacs)
when they should be instantaneous. While digging into
`url-retrieve-synchronously', I found that waiting on the correct
network process instead of passing nil to `accept-process-output' made
these network requests instantaneous (although I have no idea why). See
the attached patch.

[1]: https://github.com/KeyWeeUsr/emacs-syncthing

To test this patch, you can:

1. Run a simple web server on localhost. I usually use

    python -m http.server --bind 127.0.0.1 8000

2. Evaluate:  (benchmark 100 '(url-retrieve-synchronously "http://127.0.0.1:8000"))

With this patch, this form is ~16x faster on my machine. I've also
tested this against a remote machine with a ~45ms latency and found a
1.25x speedup.

I've confirmed that this isn't busy-waiting by modifying this code to
print a message each time it loops: it loops the same number of times
with or without my patch.

I've confirmed that this speedup is strictly due to passing the target
process to `accept-process-output' by applying my patch then changing
JUST "proc" to "nil":

                    ;; ms, so split the difference.
                    (accept-process-output proc 0.05))

to

                    ;; ms, so split the difference.
                    (accept-process-output nil 0.05))

With this one change, this code goes back to being as slow as it was before.

**Historical context**

`url-retrieve-synchronously' was changed to wait on "nil" in:

https://debbugs.gnu.org/cgi/bugreport.cgi?bug=49897,

Motivated by this bug report:

https://debbugs.gnu.org/cgi/bugreport.cgi?bug=49861

However, the patch in question also changed the rest of
`url-retrieve-synchronously' so I'm hoping the issue lies elsewhere?

In GNU Emacs 31.0.50 (build 1, x86_64-pc-linux-gnu, cairo version
 1.18.4) of 2025-06-11 built on Laptop
Repository revision: 87244ef1661f9e9d7c08f65047551e8a34cd92b2
Repository branch: makepkg
Windowing system distributor 'The X.Org Foundation', version 11.0.12101016
System Description: Arch Linux

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