[Python-checkins] bpo-1635741: Add PyModule_AddObjectRef() function (GH-23122)

Wed Nov 4 07:59:25 EST 2020

https://github.com/python/cpython/commit/8021875bbcf7385e651def51bc597472a569042c
commit: 8021875bbcf7385e651def51bc597472a569042c
branch: master
author: Victor Stinner <vstinner at python.org>
committer: vstinner <vstinner at python.org>
date: 2020年11月04日T13:59:15+01:00
summary:
bpo-1635741: Add PyModule_AddObjectRef() function (GH-23122)
Added PyModule_AddObjectRef() function: similar to
PyModule_AddObjectRef() but don't steal a reference to the value on
success.
files:
A Misc/NEWS.d/next/C API/2020-11-03-11-52-27.bpo-1635741.aDYJKB.rst
M Doc/c-api/module.rst
M Doc/whatsnew/3.10.rst
M Include/modsupport.h
M Python/modsupport.c

diff --git a/Doc/c-api/module.rst b/Doc/c-api/module.rst
index 6e9474bfa40eb..41a705d9e9915 100644
--- a/Doc/c-api/module.rst
+++ b/Doc/c-api/module.rst
@@ -264,7 +264,7 @@ of the following two module creation functions:
 instead; only use this if you are sure you need it.
 
 Before it is returned from in the initialization function, the resulting module
-object is typically populated using functions like :c:func:`PyModule_AddObject`.
+object is typically populated using functions like :c:func:`PyModule_AddObjectRef`.
 
 .. _multi-phase-initialization:
 
@@ -437,26 +437,102 @@ a function called from a module execution slot (if using multi-phase
 initialization), can use the following functions to help initialize the module
 state:
 
+.. c:function:: int PyModule_AddObjectRef(PyObject *module, const char *name, PyObject *value)
+
+ Add an object to *module* as *name*. This is a convenience function which
+ can be used from the module's initialization function.
+
+ On success, return ``0``. On error, raise an exception and return ``-1``.
+
+ Return ``NULL`` if *value* is ``NULL``. It must be called with an exception
+ raised in this case.
+
+ Example usage::
+
+ static int
+ add_spam(PyObject *module, int value)
+ {
+ PyObject *obj = PyLong_FromLong(value);
+ if (obj == NULL) {
+ return -1;
+ }
+ int res = PyModule_AddObjectRef(module, "spam", obj);
+ Py_DECREF(obj);
+ return res;
+ }
+
+ The example can also be written without checking explicitly if *obj* is
+ ``NULL``::
+
+ static int
+ add_spam(PyObject *module, int value)
+ {
+ PyObject *obj = PyLong_FromLong(value);
+ int res = PyModule_AddObjectRef(module, "spam", obj);
+ Py_XDECREF(obj);
+ return res;
+ }
+
+ Note that ``Py_XDECREF()`` should be used instead of ``Py_DECREF()`` in
+ this case, since *obj* can be ``NULL``.
+
+ .. versionadded:: 3.10
+
+
 .. c:function:: int PyModule_AddObject(PyObject *module, const char *name, PyObject *value)
 
- Add an object to *module* as *name*. This is a convenience function which can
- be used from the module's initialization function. This steals a reference to
- *value* on success. Return ``-1`` on error, ``0`` on success.
+ Similar to :c:func:`PyModule_AddObjectRef`, but steals a reference to
+ *value* on success (if it returns ``0``).
+
+ The new :c:func:`PyModule_AddObjectRef` function is recommended, since it is
+ easy to introduce reference leaks by misusing the
+ :c:func:`PyModule_AddObject` function.
 
 .. note::
 
- Unlike other functions that steal references, ``PyModule_AddObject()`` only
- decrements the reference count of *value* **on success**.
+ Unlike other functions that steal references, ``PyModule_AddObject()``
+ only decrements the reference count of *value* **on success**.
 
 This means that its return value must be checked, and calling code must
- :c:func:`Py_DECREF` *value* manually on error. Example usage::
-
- Py_INCREF(spam);
- if (PyModule_AddObject(module, "spam", spam) < 0) {
- Py_DECREF(module);
- Py_DECREF(spam);
- return NULL;
- }
+ :c:func:`Py_DECREF` *value* manually on error.
+
+ Example usage::
+
+ static int
+ add_spam(PyObject *module, int value)
+ {
+ PyObject *obj = PyLong_FromLong(value);
+ if (obj == NULL) {
+ return -1;
+ }
+ if (PyModule_AddObject(module, "spam", obj) < 0) {
+ Py_DECREF(obj);
+ return -1;
+ }
+ // PyModule_AddObject() stole a reference to obj:
+ // Py_DECREF(obj) is not needed here
+ return 0;
+ }
+
+ The example can also be written without checking explicitly if *obj* is
+ ``NULL``::
+
+ static int
+ add_spam(PyObject *module, int value)
+ {
+ PyObject *obj = PyLong_FromLong(value);
+ if (PyModule_AddObject(module, "spam", obj) < 0) {
+ Py_XDECREF(obj);
+ return -1;
+ }
+ // PyModule_AddObject() stole a reference to obj:
+ // Py_DECREF(obj) is not needed here
+ return 0;
+ }
+
+ Note that ``Py_XDECREF()`` should be used instead of ``Py_DECREF()`` in
+ this case, since *obj* can be ``NULL``.
+
 
 .. c:function:: int PyModule_AddIntConstant(PyObject *module, const char *name, long value)
 
diff --git a/Doc/whatsnew/3.10.rst b/Doc/whatsnew/3.10.rst
index 89fc300778290..9d9284897be8a 100644
--- a/Doc/whatsnew/3.10.rst
+++ b/Doc/whatsnew/3.10.rst
@@ -374,6 +374,11 @@ New Features
 * Added :c:func:`PyUnicode_AsUTF8AndSize` to the limited C API.
 (Contributed by Alex Gaynor in :issue:`41784`.)
 
+* Added :c:func:`PyModule_AddObjectRef` function: similar to
+ :c:func:`PyModule_AddObjectRef` but don't steal a reference to the value on
+ success.
+ (Contributed by Victor Stinner in :issue:`1635741`.)
+
 
 Porting to Python 3.10
 ----------------------
diff --git a/Include/modsupport.h b/Include/modsupport.h
index 4c4aab65bac10..f009d586bf620 100644
--- a/Include/modsupport.h
+++ b/Include/modsupport.h
@@ -136,7 +136,15 @@ PyAPI_FUNC(PyObject * const *) _PyArg_UnpackKeywords(
 void _PyArg_Fini(void);
 #endif /* Py_LIMITED_API */
 
-PyAPI_FUNC(int) PyModule_AddObject(PyObject *, const char *, PyObject *);
+// Add an attribute with name 'name' and value 'obj' to the module 'mod.
+// On success, return 0 on success.
+// On error, raise an exception and return -1.
+PyAPI_FUNC(int) PyModule_AddObjectRef(PyObject *mod, const char *name, PyObject *value);
+
+// Similar to PyModule_AddObjectRef() but steal a reference to 'obj'
+// (Py_DECREF(obj)) on success (if it returns 0).
+PyAPI_FUNC(int) PyModule_AddObject(PyObject *mod, const char *, PyObject *value);
+
 PyAPI_FUNC(int) PyModule_AddIntConstant(PyObject *, const char *, long);
 PyAPI_FUNC(int) PyModule_AddStringConstant(PyObject *, const char *, const char *);
 #if !defined(Py_LIMITED_API) || Py_LIMITED_API+0 >= 0x03090000
diff --git a/Misc/NEWS.d/next/C API/2020-11-03-11-52-27.bpo-1635741.aDYJKB.rst b/Misc/NEWS.d/next/C API/2020-11-03-11-52-27.bpo-1635741.aDYJKB.rst
new file mode 100644
index 0000000000000..2ab1afb922fa8
--- /dev/null
+++ b/Misc/NEWS.d/next/C API/2020-11-03-11-52-27.bpo-1635741.aDYJKB.rst	
@@ -0,0 +1,3 @@
+Added :c:func:`PyModule_AddObjectRef` function: similar to
+:c:func:`PyModule_AddObjectRef` but don't steal a reference to the value on
+success. Patch by Victor Stinner.
diff --git a/Python/modsupport.c b/Python/modsupport.c
index 2dabcf383409e..8655daa1fc5e0 100644
--- a/Python/modsupport.c
+++ b/Python/modsupport.c
@@ -634,56 +634,70 @@ va_build_stack(PyObject **small_stack, Py_ssize_t small_stack_len,
 
 
 int
-PyModule_AddObject(PyObject *m, const char *name, PyObject *o)
+PyModule_AddObjectRef(PyObject *mod, const char *name, PyObject *value)
 {
- PyObject *dict;
- if (!PyModule_Check(m)) {
+ if (!PyModule_Check(mod)) {
 PyErr_SetString(PyExc_TypeError,
- "PyModule_AddObject() needs module as first arg");
+ "PyModule_AddObjectRef() first argument "
+ "must be a module");
 return -1;
 }
- if (!o) {
- if (!PyErr_Occurred())
- PyErr_SetString(PyExc_TypeError,
- "PyModule_AddObject() needs non-NULL value");
+ if (!value) {
+ if (!PyErr_Occurred()) {
+ PyErr_SetString(PyExc_SystemError,
+ "PyModule_AddObjectRef() must be called "
+ "with an exception raised if value is NULL");
+ }
 return -1;
 }
 
- dict = PyModule_GetDict(m);
+ PyObject *dict = PyModule_GetDict(mod);
 if (dict == NULL) {
 /* Internal error -- modules must have a dict! */
 PyErr_Format(PyExc_SystemError, "module '%s' has no __dict__",
- PyModule_GetName(m));
+ PyModule_GetName(mod));
 return -1;
 }
- if (PyDict_SetItemString(dict, name, o))
+
+ if (PyDict_SetItemString(dict, name, value)) {
 return -1;
- Py_DECREF(o);
+ }
 return 0;
 }
 
+
+int
+PyModule_AddObject(PyObject *mod, const char *name, PyObject *value)
+{
+ int res = PyModule_AddObjectRef(mod, name, value);
+ if (res == 0) {
+ Py_DECREF(value);
+ }
+ return res;
+}
+
 int
 PyModule_AddIntConstant(PyObject *m, const char *name, long value)
 {
- PyObject *o = PyLong_FromLong(value);
- if (!o)
+ PyObject *obj = PyLong_FromLong(value);
+ if (!obj) {
 return -1;
- if (PyModule_AddObject(m, name, o) == 0)
- return 0;
- Py_DECREF(o);
- return -1;
+ }
+ int res = PyModule_AddObjectRef(m, name, obj);
+ Py_DECREF(obj);
+ return res;
 }
 
 int
 PyModule_AddStringConstant(PyObject *m, const char *name, const char *value)
 {
- PyObject *o = PyUnicode_FromString(value);
- if (!o)
+ PyObject *obj = PyUnicode_FromString(value);
+ if (!obj) {
 return -1;
- if (PyModule_AddObject(m, name, o) == 0)
- return 0;
- Py_DECREF(o);
- return -1;
+ }
+ int res = PyModule_AddObjectRef(m, name, obj);
+ Py_DECREF(obj);
+ return res;
 }
 
 int
@@ -696,11 +710,5 @@ PyModule_AddType(PyObject *module, PyTypeObject *type)
 const char *name = _PyType_Name(type);
 assert(name != NULL);
 
- Py_INCREF(type);
- if (PyModule_AddObject(module, name, (PyObject *)type) < 0) {
- Py_DECREF(type);
- return -1;
- }
-
- return 0;
+ return PyModule_AddObjectRef(module, name, (PyObject *)type);
 }
