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

Co-authored-by: Carol Willing <carolcode@willingconsulting.com>

diff --git a/Doc/library/os.rst b/Doc/library/os.rst
index f4566a6684e14c3fb5a6dc82b09fa6edaad761bf..2ff0b73560ac4ca3844bbbe0e277afdb0b9c4596 100644 (file)
--- a/Doc/library/os.rst
+++ b/Doc/library/os.rst
@@ -4383,6 +4383,11 @@ 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).
@@ -4422,6 +4427,11 @@ 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 af9378464edb9f69166926f57a7febd405672bcf..bd2f5ed45cb8b48e1360f8c3a9685277de74d527 100644 (file)
--- 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 040e28e9124014ba99e14a1634a3cccd2201e6a1..0e18db73280a63feaa5eacfc769b90309a6ab7df 100644 (file)
--- 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: