https://github.com/python/cpython/commit/469a56470b1d8df03862d8ceb73aebca14772dcf
commit: 469a56470b1d8df03862d8ceb73aebca14772dcf
branch: main
author: Petr Viktorin <encu...@gmail.com>
committer: AA-Turner <9087854+aa-tur...@users.noreply.github.com>
date: 2025-05-28T08:53:04+01:00
summary:
gh-134160: Block multiple module initialization (#134773)
Co-authored-by: Adam Turner <9087854+aa-tur...@users.noreply.github.com>
files:
M Doc/extending/extending.rst
diff --git a/Doc/extending/extending.rst b/Doc/extending/extending.rst
index 918c751b009761..fd63495674651b 100644
--- a/Doc/extending/extending.rst
+++ b/Doc/extending/extending.rst
@@ -204,17 +204,32 @@ value must be in a particular range or must satisfy other
conditions,
:c:data:`PyExc_ValueError` is appropriate.
You can also define a new exception that is unique to your module.
-For this, you can declare a static global object variable at the beginning
-of the file::
+The simplest way to do this is to declare a static global object variable at
+the beginning of the file::
- static PyObject *SpamError;
+ static PyObject *SpamError = NULL;
-and initialize it with an exception object in the module's
+and initialize it by calling :c:func:`PyErr_NewException` in the module's
:c:data:`Py_mod_exec` function (:c:func:`!spam_module_exec`)::
+ SpamError = PyErr_NewException("spam.error", NULL, NULL);
+
+Since :c:data:`!SpamError` is a global variable, it will be overwitten every
time
+the module is reinitialized, when the :c:data:`Py_mod_exec` function is called.
+
+For now, let's avoid the issue: we will block repeated initialization by
raising an
+:py:exc:`ImportError`::
+
+ static PyObject *SpamError = NULL;
+
static int
spam_module_exec(PyObject *m)
{
+ if (SpamError != NULL) {
+ PyErr_SetString(PyExc_ImportError,
+ "cannot initialize spam module more than once");
+ return -1;
+ }
SpamError = PyErr_NewException("spam.error", NULL, NULL);
if (PyModule_AddObjectRef(m, "SpamError", SpamError) < 0) {
return -1;
@@ -253,6 +268,11 @@ needed to ensure that it will not be discarded, causing
:c:data:`!SpamError` to
become a dangling pointer. Should it become a dangling pointer, C code which
raises the exception could cause a core dump or other unintended side effects.
+For now, the :c:func:`Py_DECREF` call to remove this reference is missing.
+Even when the Python interpreter shuts down, the global :c:data:`!SpamError`
+variable will not be garbage-collected. It will "leak".
+We did, however, ensure that this will happen at most once per process.
+
We discuss the use of :c:macro:`PyMODINIT_FUNC` as a function return type
later in this
sample.
_______________________________________________
Python-checkins mailing list -- python-checkins@python.org
To unsubscribe send an email to python-checkins-le...@python.org
https://mail.python.org/mailman3//lists/python-checkins.python.org
Member address: arch...@mail-archive.com
