From ab9f93dada34e02ebedbabc4ef007b99d545ac52 Mon Sep 17 00:00:00 2001
From: "Gregory P. Smith [Google LLC]" <greg@krypto.org>
Date: Tue, 24 Sep 2024 00:25:38 +0000
Subject: [PATCH] Add a comment about the fd recv acks.

---
 Lib/multiprocessing/reduction.py | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/Lib/multiprocessing/reduction.py b/Lib/multiprocessing/reduction.py
index c282d865a85df3..fcccd3eef86cc7 100644
--- a/Lib/multiprocessing/reduction.py
+++ b/Lib/multiprocessing/reduction.py
@@ -155,6 +155,10 @@ def recvfds(sock, size):
         if not msg and not ancdata:
             raise EOFError
         try:
+            # We send/recv an Ack byte after the fds to work around an old
+            # macOS bug; it isn't clear if this is still required but it
+            # makes unit testing fd sending easier.
+            # See: https://github.com/python/cpython/issues/58874
             sock.send(b'A')  # Acknowledge
             if len(ancdata) != 1:
                 raise RuntimeError('received %d items of ancdata' %