From 3bfe2b6c2a857f987e57ae8ab7097e113f590621 Mon Sep 17 00:00:00 2001
From: "Miss Islington (bot)"
 <31488909+miss-islington@users.noreply.github.com>
Date: Sat, 16 Dec 2023 10:12:10 +0100
Subject: [PATCH] [3.12] gh-105912: document gotcha with using os.fork on macOS
 (GH-112871) (#113133)

gh-105912: document gotcha with using os.fork on macOS (GH-112871)

* gh-105912: document gotcha with using os.fork on macOS

Using ``fork(2)`` on macOS when also using higher-level
system APIs in the parent proces can crash on macOS because
those system APIs are not written to handle this usage
pattern.

There's nothing we can do about this other than documenting
the problem.

(cherry picked from commit 22511f77c2818a138a252e6ddae89725d082f8b0)

Co-authored-by: Ronald Oussoren <ronaldoussoren@mac.com>
Co-authored-by: Carol Willing <carolcode@willingconsulting.com>
---
 Doc/library/os.rst             | 10 ++++++++++
 Doc/library/pty.rst            |  3 +++
 Doc/library/urllib.request.rst |  8 ++++++++
 3 files changed, 21 insertions(+)

diff --git a/Doc/library/os.rst b/Doc/library/os.rst
index 4507fbc8164dc8..8d92ac3957c8a5 100644
--- a/Doc/library/os.rst
+++ b/Doc/library/os.rst
@@ -4165,6 +4165,11 @@ written in Python, such as a mail server's external command delivery program.
       If you use TLS sockets in an application calling ``fork()``, see
       the warning in the :mod:`ssl` documentation.
 
+   .. warning::
+
+      On macOS the use of this function is unsafe when mixed with using
+      higher-level system APIs, and that includes using :mod:`urllib.request`.
+
    .. versionchanged:: 3.8
       Calling ``fork()`` in a subinterpreter is no longer supported
       (:exc:`RuntimeError` is raised).
@@ -4204,6 +4209,11 @@ written in Python, such as a mail server's external command delivery program.
 
    .. audit-event:: os.forkpty "" os.forkpty
 
+   .. warning::
+
+      On macOS the use of this function is unsafe when mixed with using
+      higher-level system APIs, and that includes using :mod:`urllib.request`.
+
    .. versionchanged:: 3.12
       If Python is able to detect that your process has multiple
       threads, this now raises a :exc:`DeprecationWarning`. See the
diff --git a/Doc/library/pty.rst b/Doc/library/pty.rst
index af9378464edb9f..bd2f5ed45cb8b4 100644
--- a/Doc/library/pty.rst
+++ b/Doc/library/pty.rst
@@ -33,6 +33,9 @@ The :mod:`pty` module defines the following functions:
    file descriptor connected to the child's controlling terminal (and also to the
    child's standard input and output).
 
+   .. warning:: On macOS the use of this function is unsafe when mixed with using
+      higher-level system APIs, and that includes using :mod:`urllib.request`.
+
 
 .. function:: openpty()
 
diff --git a/Doc/library/urllib.request.rst b/Doc/library/urllib.request.rst
index 690f01c93a1ee7..f55b6813d1e5bc 100644
--- a/Doc/library/urllib.request.rst
+++ b/Doc/library/urllib.request.rst
@@ -21,6 +21,14 @@ authentication, redirections, cookies and more.
     The `Requests package <https://requests.readthedocs.io/en/master/>`_
     is recommended for a higher-level HTTP client interface.
 
+.. warning::
+
+   On macOS it is unsafe to use this module in programs using
+   :func:`os.fork` because the :func:`getproxies` implementation for
+   macOS uses a higher-level system API. Set the environment variable
+   ``no_proxy`` to ``*`` to avoid this problem
+   (e.g. ``os.environ["no_proxy"] = "*"``).
+
 .. include:: ../includes/wasm-notavail.rst
 
 The :mod:`urllib.request` module defines the following functions: