gh-109047: Add PythonFinalizationError exception

Add PythonFinalizationError. This exception derived from RuntimeError
is raised when an operation is blocked during the Python
finalization.

The following functions now raise PythonFinalizationError, instead of
RuntimeError:

* _thread.start_new_thread()
* os.fork()
* os.fork1()
* os.forkpty()

Morever, _winapi.Overlapped finalizer now logs an unraisable
PythonFinalizationError, instead of an unraisable RuntimeError.

Author: vstinner

Doc/library/exceptions.rst

@@ -392,6 +392,24 @@ The following exceptions are the exceptions that are usually raised.
    handling in C, most floating point operations are not checked.
 
 
+.. exception:: PythonFinalizationError
+
+   This exception is derived from :exc:`RuntimeError`.  It is raised when
+   an operations is blocked during the :term:`Python finalization <interpreter
+   shutdown>`.
+
+   Examples of operations which can be blocked with a
+   :exc:`PythonFinalizationError` during the Python finalization:
+
+   * create a new Python thread;
+   * :func:`os.fork`.
+
+   See also the :func:`sys.is_finalizing` function.
+
+   .. versionadded:: 3.13
+      Previously, a plain :exc:`RuntimeError` was raised.
+
+
 .. exception:: RecursionError
 
    This exception is derived from :exc:`RuntimeError`.  It is raised when the

Doc/library/sys.rst

@@ -1185,6 +1185,8 @@ always available.
    Return :const:`True` if the main Python interpreter is
    :term:`shutting down <interpreter shutdown>`. Return :const:`False` otherwise.
 
+   See also the :exc:`PythonFinalizationError` exception.
+
    .. versionadded:: 3.5
 
 .. data:: last_exc

Doc/whatsnew/3.13.rst

@@ -91,6 +91,12 @@ Other Language Changes
   of the ``optimize`` argument.
   (Contributed by Irit Katriel in :gh:`108113`).
 
+* Add :exc:`PythonFinalizationError`. This exception derived from
+  :exc:`RuntimeError` is raised when an operation is blocked during
+  the :term:`Python finalization <interpreter shutdown>`.
+  (Contributed by Victor Stinner in :gh:`109047`.)
+
+
 New Modules
 ===========
 

Include/cpython/pyerrors.h

@@ -120,4 +120,6 @@ PyAPI_FUNC(void) _Py_NO_RETURN _Py_FatalErrorFunc(
     const char *func,
     const char *message);
 
+PyAPI_DATA(PyObject *) PyExc_PythonFinalizationError;
+
 #define Py_FatalError(message) _Py_FatalErrorFunc(__func__, (message))

Lib/test/exception_hierarchy.txt

@@ -40,6 +40,7 @@ BaseException
       ├── ReferenceError
       ├── RuntimeError
       │    ├── NotImplementedError
+      │    ├── PythonFinalizationError
       │    └── RecursionError
       ├── StopAsyncIteration
       ├── StopIteration

Lib/test/test_pickle.py

@@ -539,6 +539,7 @@ def test_exceptions(self):
                 if exc in (BlockingIOError,
                            ResourceWarning,
                            StopAsyncIteration,
+                           PythonFinalizationError,
                            RecursionError,
                            EncodingWarning,
                            BaseExceptionGroup,

Misc/NEWS.d/next/Core and Builtins/2023-09-25-00-48-13.gh-issue-109047.BzwMlJ.rst

@@ -0,0 +1,3 @@
+Add :exc:`PythonFinalizationError`. This exception derived from
+:exc:`RuntimeError` is raised when an operation is blocked during the
+:term:`Python finalization <interpreter shutdown>`. Patch by Victor Stinner.

Modules/_posixsubprocess.c

@@ -1030,7 +1030,7 @@ subprocess_fork_exec_impl(PyObject *module, PyObject *process_args,
 
     PyInterpreterState *interp = _PyInterpreterState_GET();
     if ((preexec_fn != Py_None) && interp->finalizing) {
-        PyErr_SetString(PyExc_RuntimeError,
+        PyErr_SetString(PyExc_PythonFinalizationError,
                         "preexec_fn not supported at interpreter shutdown");
         return NULL;
     }

Modules/_threadmodule.c

@@ -1179,7 +1179,7 @@ thread_PyThread_start_new_thread(PyObject *self, PyObject *fargs)
         return NULL;
     }
     if (interp->finalizing) {
-        PyErr_SetString(PyExc_RuntimeError,
+        PyErr_SetString(PyExc_PythonFinalizationError,
                         "can't create new thread at interpreter shutdown");
         return NULL;
     }

Modules/_winapi.c

@@ -139,7 +139,7 @@ overlapped_dealloc(OverlappedObject *self)
         {
             /* The operation is still pending -- give a warning.  This
                will probably only happen on Windows XP. */
-            PyErr_SetString(PyExc_RuntimeError,
+            PyErr_SetString(PyExc_PythonFinalizationError,
                             "I/O operations still in flight while destroying "
                             "Overlapped object, the process may crash");
             PyErr_WriteUnraisable(NULL);