May 23, 2025 · May 22, 2025
diff --git a/Doc/howto/isolating-extensions.rst b/Doc/howto/isolating-extensions.rst
 module, you can explicitly make your module loadable only once per
 process. For example::

   // A process-wide flag
   static int loaded = 0;

   // Mutex to provide thread safety (only needed for free-threaded Python)
   static PyMutex modinit_mutex = {0};

   static int
   exec_module(PyObject* module)
   {
       PyMutex_Lock(&modinit_mutex);
       if (loaded) {
           PyMutex_Unlock(&modinit_mutex);
           PyErr_SetString(PyExc_ImportError,
                           "cannot load module more than once per process");
           return -1;
       }
       loaded = 1;
       PyMutex_Unlock(&modinit_mutex);
       // ... rest of initialization
   }


 If your module's :c:member:`PyModuleDef.m_clear` function is able to prepare
 for future re-initialization, it should clear the ``loaded`` flag.
 In this case, your module won't support multiple instances existing
 *concurrently*, but it will, for example, support being loaded after
 Python runtime shutdown (:c:func:`Py_FinalizeEx`) and re-initialization
 (:c:func:`Py_Initialize`).


 Module State Access from Functions
 ----------------------------------
Original file line number	Diff line number	Diff line change
Expand Up		@@ -215,21 +215,36 @@ multiple interpreters correctly. If this is not yet the case for your
		module, you can explicitly make your module loadable only once per
		process. For example::

		// A process-wide flag
		static int loaded = 0;

		// Mutex to provide thread safety (only needed for free-threaded Python)
		static PyMutex modinit_mutex = {0};

		static int
		exec_module(PyObject* module)
		{
		PyMutex_Lock(&modinit_mutex);
		if (loaded) {
		PyMutex_Unlock(&modinit_mutex);
		PyErr_SetString(PyExc_ImportError,
		"cannot load module more than once per process");
		return -1;
		}
		loaded = 1;
		PyMutex_Unlock(&modinit_mutex);
		// ... rest of initialization
		}


		If your module's :c:member:`PyModuleDef.m_clear` function is able to prepare
		for future re-initialization, it should clear the ``loaded`` flag.
		In this case, your module won't support multiple instances existing
		concurrently, but it will, for example, support being loaded after
		Python runtime shutdown (:c:func:`Py_FinalizeEx`) and re-initialization
		(:c:func:`Py_Initialize`).


		Module State Access from Functions
		----------------------------------

Expand Down