master reporting "creating pipe: too many open files"

[Stephen Leake]

I have a custom git front-end that works fine in emacs 28, but in
current emacs master it always reports "creating pipe: too many open
files" after a commands. Then any subsequent command in emacs that
requires a file (such as saving a buffer) also fails.

This is on Windows 8.1, emacs built with mingw64.

I'm guessing there is some file/process handle that is opened and not
closed.

I update my local copy of emacs master rarely, so this change happened
sometime since Dec 2021; I have not tried to bisect.

Attached is some simplified code that shows the problem; it runs a
subprocess the same way the git front-end does. To run, load the file,
then run M-x dd-test. On my system, master is ok with 10 processes,
fails with 100 (I did not bisect further). Emacs 28 is ok forever.

Before I submit a bug report, I want to check that there is nothing
simple wrong with the code; is it relying on undocumented behaviour in
emacs 28, or something similar?

-- 
-- Stephe

debug-process.el
Description: application/emacs-lisp