https://github.com/python/cpython/commit/89c220b93c06059f623e2d232bd54f49be1be22d
commit: 89c220b93c06059f623e2d232bd54f49be1be22d
branch: main
author: Nathan Goldbaum <nathan.goldb...@gmail.com>
committer: colesbury <colesb...@gmail.com>
date: 2025-07-21T17:25:43-04:00
summary:
gh-133296: Publicly expose critical section API that accepts PyMutex (gh-135899)
This makes the following APIs public:
* `Py_BEGIN_CRITICAL_SECTION_MUTEX(mutex),`
* `Py_BEGIN_CRITICAL_SECTION2_MUTEX(mutex1, mutex2)`
* `void PyCriticalSection_BeginMutex(PyCriticalSection *c, PyMutex *mutex)`
* `void PyCriticalSection2_BeginMutex(PyCriticalSection2 *c, PyMutex *mutex1,
PyMutex *mutex2)`
The macros are identical to the corresponding `Py_BEGIN_CRITICAL_SECTION` and
`Py_BEGIN_CRITICAL_SECTION2` macros (e.g., they include braces), but they
accept a `PyMutex` instead of an object.
The new macros are still paired with the existing END macros
(`Py_END_CRITICAL_SECTION`, `Py_END_CRITICAL_SECTION2`).
files:
A Misc/NEWS.d/next/C_API/2025-06-24-11-10-01.gh-issue-133296.lIEuVJ.rst
M Doc/c-api/init.rst
M Include/cpython/critical_section.h
M Include/internal/pycore_critical_section.h
M Modules/_ctypes/ctypes.h
M Modules/_testcapimodule.c
M Objects/typeobject.c
M Python/critical_section.c
diff --git a/Doc/c-api/init.rst b/Doc/c-api/init.rst
index 409539dec17d73..d35e905b2e72df 100644
--- a/Doc/c-api/init.rst
+++ b/Doc/c-api/init.rst
@@ -2306,6 +2306,12 @@ is resumed, and its locks reacquired. This means the
critical section API
provides weaker guarantees than traditional locks -- they are useful because
their behavior is similar to the :term:`GIL`.
+Variants that accept :c:type:`PyMutex` pointers rather than Python objects are
also
+available. Use these variants to start a critical section in a situation where
+there is no :c:type:`PyObject` -- for example, when working with a C type that
+does not extend or wrap :c:type:`PyObject` but still needs to call into the C
+API in a manner that might lead to deadlocks.
+
The functions and structs used by the macros are exposed for cases
where C macros are not available. They should only be used as in the
given macro expansions. Note that the sizes and contents of the structures may
@@ -2351,6 +2357,23 @@ code triggered by the finalizer blocks and calls
:c:func:`PyEval_SaveThread`.
.. versionadded:: 3.13
+.. c:macro:: Py_BEGIN_CRITICAL_SECTION_MUTEX(m)
+
+ Locks the mutex *m* and begins a critical section.
+
+ In the free-threaded build, this macro expands to::
+
+ {
+ PyCriticalSection _py_cs;
+ PyCriticalSection_BeginMutex(&_py_cs, m)
+
+ Note that unlike :c:macro:`Py_BEGIN_CRITICAL_SECTION`, there is no cast for
+ the argument of the macro - it must be a :c:type:`PyMutex` pointer.
+
+ On the default build, this macro expands to ``{``.
+
+ .. versionadded:: next
+
.. c:macro:: Py_END_CRITICAL_SECTION()
Ends the critical section and releases the per-object lock.
@@ -2380,6 +2403,23 @@ code triggered by the finalizer blocks and calls
:c:func:`PyEval_SaveThread`.
.. versionadded:: 3.13
+.. c:macro:: Py_BEGIN_CRITICAL_SECTION2_MUTEX(m1, m2)
+
+ Locks the mutexes *m1* and *m2* and begins a critical section.
+
+ In the free-threaded build, this macro expands to::
+
+ {
+ PyCriticalSection2 _py_cs2;
+ PyCriticalSection2_BeginMutex(&_py_cs2, m1, m2)
+
+ Note that unlike :c:macro:`Py_BEGIN_CRITICAL_SECTION2`, there is no cast for
+ the arguments of the macro - they must be :c:type:`PyMutex` pointers.
+
+ On the default build, this macro expands to ``{``.
+
+ .. versionadded:: next
+
.. c:macro:: Py_END_CRITICAL_SECTION2()
Ends the critical section and releases the per-object locks.
diff --git a/Include/cpython/critical_section.h
b/Include/cpython/critical_section.h
index 35db3fb6a59ce6..4fc46fefb93a24 100644
--- a/Include/cpython/critical_section.h
+++ b/Include/cpython/critical_section.h
@@ -73,22 +73,32 @@ typedef struct PyCriticalSection2 PyCriticalSection2;
PyAPI_FUNC(void)
PyCriticalSection_Begin(PyCriticalSection *c, PyObject *op);
+PyAPI_FUNC(void)
+PyCriticalSection_BeginMutex(PyCriticalSection *c, PyMutex *m);
+
PyAPI_FUNC(void)
PyCriticalSection_End(PyCriticalSection *c);
PyAPI_FUNC(void)
PyCriticalSection2_Begin(PyCriticalSection2 *c, PyObject *a, PyObject *b);
+PyAPI_FUNC(void)
+PyCriticalSection2_BeginMutex(PyCriticalSection2 *c, PyMutex *m1, PyMutex *m2);
+
PyAPI_FUNC(void)
PyCriticalSection2_End(PyCriticalSection2 *c);
#ifndef Py_GIL_DISABLED
# define Py_BEGIN_CRITICAL_SECTION(op) \
{
+# define Py_BEGIN_CRITICAL_SECTION_MUTEX(mutex) \
+ {
# define Py_END_CRITICAL_SECTION() \
}
# define Py_BEGIN_CRITICAL_SECTION2(a, b) \
{
+# define Py_BEGIN_CRITICAL_SECTION2_MUTEX(m1, m2) \
+ {
# define Py_END_CRITICAL_SECTION2() \
}
#else /* !Py_GIL_DISABLED */
@@ -118,6 +128,11 @@ struct PyCriticalSection2 {
PyCriticalSection _py_cs; \
PyCriticalSection_Begin(&_py_cs, _PyObject_CAST(op))
+# define Py_BEGIN_CRITICAL_SECTION_MUTEX(mutex) \
+ { \
+ PyCriticalSection _py_cs; \
+ PyCriticalSection_BeginMutex(&_py_cs, mutex)
+
# define Py_END_CRITICAL_SECTION() \
PyCriticalSection_End(&_py_cs); \
}
@@ -127,6 +142,11 @@ struct PyCriticalSection2 {
PyCriticalSection2 _py_cs2; \
PyCriticalSection2_Begin(&_py_cs2, _PyObject_CAST(a),
_PyObject_CAST(b))
+# define Py_BEGIN_CRITICAL_SECTION2_MUTEX(m1, m2) \
+ { \
+ PyCriticalSection2 _py_cs2; \
+ PyCriticalSection2_BeginMutex(&_py_cs2, m1, m2)
+
# define Py_END_CRITICAL_SECTION2() \
PyCriticalSection2_End(&_py_cs2); \
}
diff --git a/Include/internal/pycore_critical_section.h
b/Include/internal/pycore_critical_section.h
index 62460c5f8fad30..2601de40737e85 100644
--- a/Include/internal/pycore_critical_section.h
+++ b/Include/internal/pycore_critical_section.h
@@ -21,16 +21,6 @@ extern "C" {
#define _Py_CRITICAL_SECTION_MASK 0x3
#ifdef Py_GIL_DISABLED
-# define Py_BEGIN_CRITICAL_SECTION_MUT(mutex) \
- { \
- PyCriticalSection _py_cs; \
- _PyCriticalSection_BeginMutex(&_py_cs, mutex)
-
-# define Py_BEGIN_CRITICAL_SECTION2_MUT(m1, m2) \
- { \
- PyCriticalSection2 _py_cs2; \
- _PyCriticalSection2_BeginMutex(&_py_cs2, m1, m2)
-
// Specialized version of critical section locking to safely use
// PySequence_Fast APIs without the GIL. For performance, the argument *to*
// PySequence_Fast() is provided to the macro, not the *result* of
@@ -75,8 +65,6 @@ extern "C" {
#else /* !Py_GIL_DISABLED */
// The critical section APIs are no-ops with the GIL.
-# define Py_BEGIN_CRITICAL_SECTION_MUT(mut) {
-# define Py_BEGIN_CRITICAL_SECTION2_MUT(m1, m2) {
# define Py_BEGIN_CRITICAL_SECTION_SEQUENCE_FAST(original) {
# define Py_END_CRITICAL_SECTION_SEQUENCE_FAST() }
# define _Py_CRITICAL_SECTION_ASSERT_MUTEX_LOCKED(mutex)
@@ -119,6 +107,7 @@ _PyCriticalSection_BeginMutex(PyCriticalSection *c, PyMutex
*m)
_PyCriticalSection_BeginSlow(c, m);
}
}
+#define PyCriticalSection_BeginMutex _PyCriticalSection_BeginMutex
static inline void
_PyCriticalSection_Begin(PyCriticalSection *c, PyObject *op)
@@ -194,6 +183,7 @@ _PyCriticalSection2_BeginMutex(PyCriticalSection2 *c,
PyMutex *m1, PyMutex *m2)
_PyCriticalSection2_BeginSlow(c, m1, m2, 0);
}
}
+#define PyCriticalSection2_BeginMutex _PyCriticalSection2_BeginMutex
static inline void
_PyCriticalSection2_Begin(PyCriticalSection2 *c, PyObject *a, PyObject *b)
diff --git
a/Misc/NEWS.d/next/C_API/2025-06-24-11-10-01.gh-issue-133296.lIEuVJ.rst
b/Misc/NEWS.d/next/C_API/2025-06-24-11-10-01.gh-issue-133296.lIEuVJ.rst
new file mode 100644
index 00000000000000..41401911a6bc0b
--- /dev/null
+++ b/Misc/NEWS.d/next/C_API/2025-06-24-11-10-01.gh-issue-133296.lIEuVJ.rst
@@ -0,0 +1,3 @@
+New variants for the critical section API that accept one or two
+:c:type:`PyMutex` pointers rather than :c:type:`PyObject` instances are now
+public in the non-limited C API.
diff --git a/Modules/_ctypes/ctypes.h b/Modules/_ctypes/ctypes.h
index 5b4f97d43b8721..9f995bf24080a5 100644
--- a/Modules/_ctypes/ctypes.h
+++ b/Modules/_ctypes/ctypes.h
@@ -431,7 +431,7 @@ typedef struct {
visible to other threads before the `dict_final` bit is set.
*/
-#define STGINFO_LOCK(stginfo)
Py_BEGIN_CRITICAL_SECTION_MUT(&(stginfo)->mutex)
+#define STGINFO_LOCK(stginfo)
Py_BEGIN_CRITICAL_SECTION_MUTEX(&(stginfo)->mutex)
#define STGINFO_UNLOCK() Py_END_CRITICAL_SECTION()
static inline uint8_t
diff --git a/Modules/_testcapimodule.c b/Modules/_testcapimodule.c
index 334f2a53041ca4..d0c0b45c20cb36 100644
--- a/Modules/_testcapimodule.c
+++ b/Modules/_testcapimodule.c
@@ -2418,6 +2418,16 @@ test_critical_sections(PyObject *module, PyObject
*Py_UNUSED(args))
Py_BEGIN_CRITICAL_SECTION2(module, module);
Py_END_CRITICAL_SECTION2();
+#ifdef Py_GIL_DISABLED
+ // avoid unused variable compiler warning on GIL-enabled build
+ PyMutex mut = {0};
+ Py_BEGIN_CRITICAL_SECTION_MUTEX(&mut);
+ Py_END_CRITICAL_SECTION();
+
+ Py_BEGIN_CRITICAL_SECTION2_MUTEX(&mut, &mut);
+ Py_END_CRITICAL_SECTION2();
+#endif
+
Py_RETURN_NONE;
}
diff --git a/Objects/typeobject.c b/Objects/typeobject.c
index 379c4d0467c487..d952a58d94af55 100644
--- a/Objects/typeobject.c
+++ b/Objects/typeobject.c
@@ -73,11 +73,11 @@ class object "PyObject *" "&PyBaseObject_Type"
// while the stop-the-world mechanism is active. The slots and flags are read
// in many places without holding a lock and without atomics.
#define TYPE_LOCK &PyInterpreterState_Get()->types.mutex
-#define BEGIN_TYPE_LOCK() Py_BEGIN_CRITICAL_SECTION_MUT(TYPE_LOCK)
+#define BEGIN_TYPE_LOCK() Py_BEGIN_CRITICAL_SECTION_MUTEX(TYPE_LOCK)
#define END_TYPE_LOCK() Py_END_CRITICAL_SECTION()
#define BEGIN_TYPE_DICT_LOCK(d) \
- Py_BEGIN_CRITICAL_SECTION2_MUT(TYPE_LOCK, &_PyObject_CAST(d)->ob_mutex)
+ Py_BEGIN_CRITICAL_SECTION2_MUTEX(TYPE_LOCK, &_PyObject_CAST(d)->ob_mutex)
#define END_TYPE_DICT_LOCK() Py_END_CRITICAL_SECTION2()
diff --git a/Python/critical_section.c b/Python/critical_section.c
index 73857b85496316..e628ba2f6d19bc 100644
--- a/Python/critical_section.c
+++ b/Python/critical_section.c
@@ -130,6 +130,15 @@ PyCriticalSection_Begin(PyCriticalSection *c, PyObject *op)
#endif
}
+#undef PyCriticalSection_BeginMutex
+void
+PyCriticalSection_BeginMutex(PyCriticalSection *c, PyMutex *m)
+{
+#ifdef Py_GIL_DISABLED
+ _PyCriticalSection_BeginMutex(c, m);
+#endif
+}
+
#undef PyCriticalSection_End
void
PyCriticalSection_End(PyCriticalSection *c)
@@ -148,6 +157,15 @@ PyCriticalSection2_Begin(PyCriticalSection2 *c, PyObject
*a, PyObject *b)
#endif
}
+#undef PyCriticalSection2_BeginMutex
+void
+PyCriticalSection2_BeginMutex(PyCriticalSection2 *c, PyMutex *m1, PyMutex *m2)
+{
+#ifdef Py_GIL_DISABLED
+ _PyCriticalSection2_BeginMutex(c, m1, m2);
+#endif
+}
+
#undef PyCriticalSection2_End
void
PyCriticalSection2_End(PyCriticalSection2 *c)
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