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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`).
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‎Doc/c-api/init.rst

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@@ -2306,6 +2306,12 @@ is resumed, and its locks reacquired. This means the critical section API
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provides weaker guarantees than traditional locks -- they are useful because
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their behavior is similar to the :term:`GIL`.
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Variants that accept :c:type:`PyMutex` pointers rather than Python objects are also
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available. Use these variants to start a critical section in a situation where
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there is no :c:type:`PyObject` -- for example, when working with a C type that
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does not extend or wrap :c:type:`PyObject` but still needs to call into the C
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API in a manner that might lead to deadlocks.
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The functions and structs used by the macros are exposed for cases
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where C macros are not available. They should only be used as in the
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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`.
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.. versionadded:: 3.13
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.. c:macro:: Py_BEGIN_CRITICAL_SECTION_MUTEX(m)
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Locks the mutex *m* and begins a critical section.
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In the free-threaded build, this macro expands to::
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{
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PyCriticalSection _py_cs;
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PyCriticalSection_BeginMutex(&_py_cs, m)
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Note that unlike :c:macro:`Py_BEGIN_CRITICAL_SECTION`, there is no cast for
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the argument of the macro - it must be a :c:type:`PyMutex` pointer.
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On the default build, this macro expands to ``{``.
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.. versionadded:: next
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.. c:macro:: Py_END_CRITICAL_SECTION()
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Ends the critical section and releases the per-object lock.
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.. versionadded:: 3.13
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.. c:macro:: Py_BEGIN_CRITICAL_SECTION2_MUTEX(m1, m2)
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Locks the mutexes *m1* and *m2* and begins a critical section.
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In the free-threaded build, this macro expands to::
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{
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PyCriticalSection2 _py_cs2;
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PyCriticalSection2_BeginMutex(&_py_cs2, m1, m2)
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Note that unlike :c:macro:`Py_BEGIN_CRITICAL_SECTION2`, there is no cast for
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the arguments of the macro - they must be :c:type:`PyMutex` pointers.
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On the default build, this macro expands to ``{``.
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.. versionadded:: next
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.. c:macro:: Py_END_CRITICAL_SECTION2()
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Ends the critical section and releases the per-object locks.

‎Include/cpython/critical_section.h

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@@ -73,22 +73,32 @@ typedef struct PyCriticalSection2 PyCriticalSection2;
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PyAPI_FUNC(void)
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PyCriticalSection_Begin(PyCriticalSection *c, PyObject *op);
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PyAPI_FUNC(void)
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PyCriticalSection_BeginMutex(PyCriticalSection *c, PyMutex *m);
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PyAPI_FUNC(void)
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PyCriticalSection_End(PyCriticalSection *c);
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PyAPI_FUNC(void)
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PyCriticalSection2_Begin(PyCriticalSection2 *c, PyObject *a, PyObject *b);
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PyAPI_FUNC(void)
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PyCriticalSection2_BeginMutex(PyCriticalSection2 *c, PyMutex *m1, PyMutex *m2);
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PyAPI_FUNC(void)
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PyCriticalSection2_End(PyCriticalSection2 *c);
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#ifndef Py_GIL_DISABLED
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# define Py_BEGIN_CRITICAL_SECTION(op) \
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{
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# define Py_BEGIN_CRITICAL_SECTION_MUTEX(mutex) \
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{
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# define Py_END_CRITICAL_SECTION() \
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}
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# define Py_BEGIN_CRITICAL_SECTION2(a, b) \
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{
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# define Py_BEGIN_CRITICAL_SECTION2_MUTEX(m1, m2) \
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{
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# define Py_END_CRITICAL_SECTION2() \
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}
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#else /* !Py_GIL_DISABLED */
@@ -118,6 +128,11 @@ struct PyCriticalSection2 {
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PyCriticalSection _py_cs; \
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PyCriticalSection_Begin(&_py_cs, _PyObject_CAST(op))
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# define Py_BEGIN_CRITICAL_SECTION_MUTEX(mutex) \
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{ \
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PyCriticalSection _py_cs; \
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PyCriticalSection_BeginMutex(&_py_cs, mutex)
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# define Py_END_CRITICAL_SECTION() \
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PyCriticalSection_End(&_py_cs); \
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}
@@ -127,6 +142,11 @@ struct PyCriticalSection2 {
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PyCriticalSection2 _py_cs2; \
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PyCriticalSection2_Begin(&_py_cs2, _PyObject_CAST(a), _PyObject_CAST(b))
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# define Py_BEGIN_CRITICAL_SECTION2_MUTEX(m1, m2) \
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{ \
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PyCriticalSection2 _py_cs2; \
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PyCriticalSection2_BeginMutex(&_py_cs2, m1, m2)
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# define Py_END_CRITICAL_SECTION2() \
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PyCriticalSection2_End(&_py_cs2); \
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}

‎Include/internal/pycore_critical_section.h

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@@ -21,16 +21,6 @@ extern "C" {
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#define _Py_CRITICAL_SECTION_MASK 0x3
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#ifdef Py_GIL_DISABLED
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# define Py_BEGIN_CRITICAL_SECTION_MUT(mutex) \
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{ \
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PyCriticalSection _py_cs; \
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_PyCriticalSection_BeginMutex(&_py_cs, mutex)
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# define Py_BEGIN_CRITICAL_SECTION2_MUT(m1, m2) \
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{ \
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PyCriticalSection2 _py_cs2; \
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_PyCriticalSection2_BeginMutex(&_py_cs2, m1, m2)
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// Specialized version of critical section locking to safely use
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// PySequence_Fast APIs without the GIL. For performance, the argument *to*
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// PySequence_Fast() is provided to the macro, not the *result* of
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#else /* !Py_GIL_DISABLED */
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// The critical section APIs are no-ops with the GIL.
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# define Py_BEGIN_CRITICAL_SECTION_MUT(mut) {
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# define Py_BEGIN_CRITICAL_SECTION2_MUT(m1, m2) {
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# define Py_BEGIN_CRITICAL_SECTION_SEQUENCE_FAST(original) {
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# define Py_END_CRITICAL_SECTION_SEQUENCE_FAST() }
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# define _Py_CRITICAL_SECTION_ASSERT_MUTEX_LOCKED(mutex)
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_PyCriticalSection_BeginSlow(c, m);
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}
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}
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#define PyCriticalSection_BeginMutex _PyCriticalSection_BeginMutex
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static inline void
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_PyCriticalSection_Begin(PyCriticalSection *c, PyObject *op)
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_PyCriticalSection2_BeginSlow(c, m1, m2, 0);
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}
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}
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#define PyCriticalSection2_BeginMutex _PyCriticalSection2_BeginMutex
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static inline void
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_PyCriticalSection2_Begin(PyCriticalSection2 *c, PyObject *a, PyObject *b)

‎Misc/NEWS.d/next/C_API/2025-06-24-11-10-01.gh-issue-133296.lIEuVJ.rst

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New variants for the critical section API that accept one or two
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:c:type:`PyMutex` pointers rather than :c:type:`PyObject` instances are now
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public in the non-limited C API.

‎Modules/_ctypes/ctypes.h

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@@ -431,7 +431,7 @@ typedef struct {
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visible to other threads before the `dict_final` bit is set.
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*/
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#define STGINFO_LOCK(stginfo) Py_BEGIN_CRITICAL_SECTION_MUT(&(stginfo)->mutex)
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#define STGINFO_LOCK(stginfo) Py_BEGIN_CRITICAL_SECTION_MUTEX(&(stginfo)->mutex)
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#define STGINFO_UNLOCK() Py_END_CRITICAL_SECTION()
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static inline uint8_t

‎Modules/_testcapimodule.c

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@@ -2418,6 +2418,16 @@ test_critical_sections(PyObject *module, PyObject *Py_UNUSED(args))
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Py_BEGIN_CRITICAL_SECTION2(module, module);
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Py_END_CRITICAL_SECTION2();
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#ifdef Py_GIL_DISABLED
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// avoid unused variable compiler warning on GIL-enabled build
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PyMutex mut = {0};
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Py_BEGIN_CRITICAL_SECTION_MUTEX(&mut);
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Py_END_CRITICAL_SECTION();
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Py_BEGIN_CRITICAL_SECTION2_MUTEX(&mut, &mut);
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Py_END_CRITICAL_SECTION2();
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#endif
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Py_RETURN_NONE;
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}
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‎Objects/typeobject.c

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@@ -73,11 +73,11 @@ class object "PyObject *" "&PyBaseObject_Type"
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// while the stop-the-world mechanism is active. The slots and flags are read
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// in many places without holding a lock and without atomics.
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#define TYPE_LOCK &PyInterpreterState_Get()->types.mutex
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#define BEGIN_TYPE_LOCK() Py_BEGIN_CRITICAL_SECTION_MUT(TYPE_LOCK)
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#define BEGIN_TYPE_LOCK() Py_BEGIN_CRITICAL_SECTION_MUTEX(TYPE_LOCK)
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#define END_TYPE_LOCK() Py_END_CRITICAL_SECTION()
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#define BEGIN_TYPE_DICT_LOCK(d) \
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Py_BEGIN_CRITICAL_SECTION2_MUT(TYPE_LOCK, &_PyObject_CAST(d)->ob_mutex)
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Py_BEGIN_CRITICAL_SECTION2_MUTEX(TYPE_LOCK, &_PyObject_CAST(d)->ob_mutex)
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#define END_TYPE_DICT_LOCK() Py_END_CRITICAL_SECTION2()
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‎Python/critical_section.c

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@@ -130,6 +130,15 @@ PyCriticalSection_Begin(PyCriticalSection *c, PyObject *op)
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#endif
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}
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#undef PyCriticalSection_BeginMutex
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void
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PyCriticalSection_BeginMutex(PyCriticalSection *c, PyMutex *m)
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{
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#ifdef Py_GIL_DISABLED
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_PyCriticalSection_BeginMutex(c, m);
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#endif
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}
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#undef PyCriticalSection_End
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void
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PyCriticalSection_End(PyCriticalSection *c)
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#endif
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}
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#undef PyCriticalSection2_BeginMutex
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void
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PyCriticalSection2_BeginMutex(PyCriticalSection2 *c, PyMutex *m1, PyMutex *m2)
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{
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#ifdef Py_GIL_DISABLED
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_PyCriticalSection2_BeginMutex(c, m1, m2);
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#endif
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}
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#undef PyCriticalSection2_End
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void
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PyCriticalSection2_End(PyCriticalSection2 *c)

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