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gh-119344: Make critical section API public (#119353)

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This makes the following macros public as part of the non-limited C-API for
locking a single object or two objects at once.

* `Py_BEGIN_CRITICAL_SECTION(op)` / `Py_END_CRITICAL_SECTION()`
* `Py_BEGIN_CRITICAL_SECTION2(a, b)` / `Py_END_CRITICAL_SECTION2()`

The supporting functions and structs used by the macros are also exposed for
cases where C macros are not available.
This commit is contained in:
Sam Gross 2024-06-21 15:50:18 -04:00 committed by GitHub
parent 03fa2df927
commit 8f17d69b7b
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GPG Key ID: B5690EEEBB952194
15 changed files with 459 additions and 225 deletions
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104
Doc/c-api/init.rst
View File

@ -2202,3 +2202,107 @@ The C-API provides a basic mutual exclusion lock.
issue a fatal error.
.. versionadded:: 3.13
.. _python-critical-section-api:
Python Critical Section API
---------------------------
The critical section API provides a deadlock avoidance layer on top of
per-object locks for :term:`free-threaded <free threading>` CPython. They are
intended to replace reliance on the :term:`global interpreter lock`, and are
no-ops in versions of Python with the global interpreter lock.
Critical sections avoid deadlocks by implicitly suspending active critical
sections and releasing the locks during calls to :c:func:`PyEval_SaveThread`.
When :c:func:`PyEval_RestoreThread` is called, the most recent critical section
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`.
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
change in future Python versions.
.. note::
Operations that need to lock two objects at once must use
:c:macro:`Py_BEGIN_CRITICAL_SECTION2`. You *cannot* use nested critical
sections to lock more than one object at once, because the inner critical
section may suspend the outer critical sections. This API does not provide
a way to lock more than two objects at once.
Example usage::
static PyObject *
set_field(MyObject *self, PyObject *value)
{
Py_BEGIN_CRITICAL_SECTION(self);
Py_SETREF(self->field, Py_XNewRef(value));
Py_END_CRITICAL_SECTION();
Py_RETURN_NONE;
}
In the above example, :c:macro:`Py_SETREF` calls :c:macro:`Py_DECREF`, which
can call arbitrary code through an object's deallocation function. The critical
section API avoids potentital deadlocks due to reentrancy and lock ordering
by allowing the runtime to temporarily suspend the critical section if the
code triggered by the finalizer blocks and calls :c:func:`PyEval_SaveThread`.
.. c:macro:: Py_BEGIN_CRITICAL_SECTION(op)
Acquires the per-object lock for the object *op* and begins a
critical section.
In the free-threaded build, this macro expands to::
{
PyCriticalSection _py_cs;
PyCriticalSection_Begin(&_py_cs, (PyObject*)(op))
In the default build, this macro expands to ``{``.
.. versionadded:: 3.13
.. c:macro:: Py_END_CRITICAL_SECTION()
Ends the critical section and releases the per-object lock.
In the free-threaded build, this macro expands to::
PyCriticalSection_End(&_py_cs);
}
In the default build, this macro expands to ``}``.
.. versionadded:: 3.13
.. c:macro:: Py_BEGIN_CRITICAL_SECTION2(a, b)
Acquires the per-objects locks for the objects *a* and *b* and begins a
critical section. The locks are acquired in a consistent order (lowest
address first) to avoid lock ordering deadlocks.
In the free-threaded build, this macro expands to::
{
PyCriticalSection2 _py_cs2;
PyCriticalSection_Begin2(&_py_cs2, (PyObject*)(a), (PyObject*)(b))
In the default build, this macro expands to ``{``.
.. versionadded:: 3.13
.. c:macro:: Py_END_CRITICAL_SECTION2()
Ends the critical section and releases the per-object locks.
In the free-threaded build, this macro expands to::
PyCriticalSection_End2(&_py_cs2);
}
In the default build, this macro expands to ``}``.
.. versionadded:: 3.13

1
Include/Python.h
View File

@ -125,6 +125,7 @@
#include "import.h"
#include "abstract.h"
#include "bltinmodule.h"
#include "critical_section.h"
#include "cpython/pyctype.h"
#include "pystrtod.h"
#include "pystrcmp.h"

134
Include/cpython/critical_section.h Normal file
View File

@ -0,0 +1,134 @@
#ifndef Py_CPYTHON_CRITICAL_SECTION_H
# error "this header file must not be included directly"
#endif
// Python critical sections
//
// Conceptually, critical sections are a deadlock avoidance layer on top of
// per-object locks. These helpers, in combination with those locks, replace
// our usage of the global interpreter lock to provide thread-safety for
// otherwise thread-unsafe objects, such as dict.
//
// NOTE: These APIs are no-ops in non-free-threaded builds.
//
// Straightforward per-object locking could introduce deadlocks that were not
// present when running with the GIL. Threads may hold locks for multiple
// objects simultaneously because Python operations can nest. If threads were
// to acquire the same locks in different orders, they would deadlock.
//
// One way to avoid deadlocks is to allow threads to hold only the lock (or
// locks) for a single operation at a time (typically a single lock, but some
// operations involve two locks). When a thread begins a nested operation it
// could suspend the locks for any outer operation: before beginning the nested
// operation, the locks for the outer operation are released and when the
// nested operation completes, the locks for the outer operation are
// reacquired.
//
// To improve performance, this API uses a variation of the above scheme.
// Instead of immediately suspending locks any time a nested operation begins,
// locks are only suspended if the thread would block. This reduces the number
// of lock acquisitions and releases for nested operations, while still
// avoiding deadlocks.
//
// Additionally, the locks for any active operation are suspended around
// other potentially blocking operations, such as I/O. This is because the
// interaction between locks and blocking operations can lead to deadlocks in
// the same way as the interaction between multiple locks.
//
// Each thread's critical sections and their corresponding locks are tracked in
// a stack in `PyThreadState.critical_section`. When a thread calls
// `_PyThreadState_Detach()`, such as before a blocking I/O operation or when
// waiting to acquire a lock, the thread suspends all of its active critical
// sections, temporarily releasing the associated locks. When the thread calls
// `_PyThreadState_Attach()`, it resumes the top-most (i.e., most recent)
// critical section by reacquiring the associated lock or locks. See
// `_PyCriticalSection_Resume()`.
//
// NOTE: Only the top-most critical section is guaranteed to be active.
// Operations that need to lock two objects at once must use
// `Py_BEGIN_CRITICAL_SECTION2()`. You *CANNOT* use nested critical sections
// to lock more than one object at once, because the inner critical section
// may suspend the outer critical sections. This API does not provide a way
// to lock more than two objects at once (though it could be added later
// if actually needed).
//
// NOTE: Critical sections implicitly behave like reentrant locks because
// attempting to acquire the same lock will suspend any outer (earlier)
// critical sections. However, they are less efficient for this use case than
// purposefully designed reentrant locks.
//
// Example usage:
// Py_BEGIN_CRITICAL_SECTION(op);
// ...
// Py_END_CRITICAL_SECTION();
//
// To lock two objects at once:
// Py_BEGIN_CRITICAL_SECTION2(op1, op2);
// ...
// Py_END_CRITICAL_SECTION2();
typedef struct PyCriticalSection PyCriticalSection;
typedef struct PyCriticalSection2 PyCriticalSection2;
PyAPI_FUNC(void)
PyCriticalSection_Begin(PyCriticalSection *c, PyObject *op);
PyAPI_FUNC(void)
PyCriticalSection_End(PyCriticalSection *c);
PyAPI_FUNC(void)
PyCriticalSection2_Begin(PyCriticalSection2 *c, PyObject *a, PyObject *b);
PyAPI_FUNC(void)
PyCriticalSection2_End(PyCriticalSection2 *c);
#ifndef Py_GIL_DISABLED
# define Py_BEGIN_CRITICAL_SECTION(op) \
{
# define Py_END_CRITICAL_SECTION() \
}
# define Py_BEGIN_CRITICAL_SECTION2(a, b) \
{
# define Py_END_CRITICAL_SECTION2() \
}
#else /* !Py_GIL_DISABLED */
// NOTE: the contents of this struct are private and may change betweeen
// Python releases without a deprecation period.
struct PyCriticalSection {
// Tagged pointer to an outer active critical section (or 0).
uintptr_t _cs_prev;
// Mutex used to protect critical section
PyMutex *_cs_mutex;
};
// A critical section protected by two mutexes. Use
// Py_BEGIN_CRITICAL_SECTION2 and Py_END_CRITICAL_SECTION2.
// NOTE: the contents of this struct are private and may change betweeen
// Python releases without a deprecation period.
struct PyCriticalSection2 {
PyCriticalSection _cs_base;
PyMutex *_cs_mutex2;
};
# define Py_BEGIN_CRITICAL_SECTION(op) \
{ \
PyCriticalSection _py_cs; \
PyCriticalSection_Begin(&_py_cs, _PyObject_CAST(op))
# define Py_END_CRITICAL_SECTION() \
PyCriticalSection_End(&_py_cs); \
}
# define Py_BEGIN_CRITICAL_SECTION2(a, b) \
{ \
PyCriticalSection2 _py_cs2; \
PyCriticalSection2_Begin(&_py_cs2, _PyObject_CAST(a), _PyObject_CAST(b))
# define Py_END_CRITICAL_SECTION2() \
PyCriticalSection2_End(&_py_cs2); \
}
#endif

16
Include/critical_section.h Normal file
View File

@ -0,0 +1,16 @@
#ifndef Py_CRITICAL_SECTION_H
#define Py_CRITICAL_SECTION_H
#ifdef __cplusplus
extern "C" {
#endif
#ifndef Py_LIMITED_API
# define Py_CPYTHON_CRITICAL_SECTION_H
# include "cpython/critical_section.h"
# undef Py_CPYTHON_CRITICAL_SECTION_H
#endif
#ifdef __cplusplus
}
#endif
#endif /* !Py_CRITICAL_SECTION_H */

218
Include/internal/pycore_critical_section.h
View File

@ -13,75 +13,9 @@
extern "C" {
#endif
// Implementation of Python critical sections
//
// Conceptually, critical sections are a deadlock avoidance layer on top of
// per-object locks. These helpers, in combination with those locks, replace
// our usage of the global interpreter lock to provide thread-safety for
// otherwise thread-unsafe objects, such as dict.
//
// NOTE: These APIs are no-ops in non-free-threaded builds.
//
// Straightforward per-object locking could introduce deadlocks that were not
// present when running with the GIL. Threads may hold locks for multiple
// objects simultaneously because Python operations can nest. If threads were
// to acquire the same locks in different orders, they would deadlock.
//
// One way to avoid deadlocks is to allow threads to hold only the lock (or
// locks) for a single operation at a time (typically a single lock, but some
// operations involve two locks). When a thread begins a nested operation it
// could suspend the locks for any outer operation: before beginning the nested
// operation, the locks for the outer operation are released and when the
// nested operation completes, the locks for the outer operation are
// reacquired.
//
// To improve performance, this API uses a variation of the above scheme.
// Instead of immediately suspending locks any time a nested operation begins,
// locks are only suspended if the thread would block. This reduces the number
// of lock acquisitions and releases for nested operations, while still
// avoiding deadlocks.
//
// Additionally, the locks for any active operation are suspended around
// other potentially blocking operations, such as I/O. This is because the
// interaction between locks and blocking operations can lead to deadlocks in
// the same way as the interaction between multiple locks.
//
// Each thread's critical sections and their corresponding locks are tracked in
// a stack in `PyThreadState.critical_section`. When a thread calls
// `_PyThreadState_Detach()`, such as before a blocking I/O operation or when
// waiting to acquire a lock, the thread suspends all of its active critical
// sections, temporarily releasing the associated locks. When the thread calls
// `_PyThreadState_Attach()`, it resumes the top-most (i.e., most recent)
// critical section by reacquiring the associated lock or locks. See
// `_PyCriticalSection_Resume()`.
//
// NOTE: Only the top-most critical section is guaranteed to be active.
// Operations that need to lock two objects at once must use
// `Py_BEGIN_CRITICAL_SECTION2()`. You *CANNOT* use nested critical sections
// to lock more than one object at once, because the inner critical section
// may suspend the outer critical sections. This API does not provide a way
// to lock more than two objects at once (though it could be added later
// if actually needed).
//
// NOTE: Critical sections implicitly behave like reentrant locks because
// attempting to acquire the same lock will suspend any outer (earlier)
// critical sections. However, they are less efficient for this use case than
// purposefully designed reentrant locks.
//
// Example usage:
// Py_BEGIN_CRITICAL_SECTION(op);
// ...
// Py_END_CRITICAL_SECTION();
//
// To lock two objects at once:
// Py_BEGIN_CRITICAL_SECTION2(op1, op2);
// ...
// Py_END_CRITICAL_SECTION2();
// Tagged pointers to critical sections use the two least significant bits to
// mark if the pointed-to critical section is inactive and whether it is a
// _PyCriticalSection2 object.
// PyCriticalSection2 object.
#define _Py_CRITICAL_SECTION_INACTIVE 0x1
#define _Py_CRITICAL_SECTION_TWO_MUTEXES 0x2
#define _Py_CRITICAL_SECTION_MASK 0x3
@ -89,24 +23,13 @@ extern "C" {
#ifdef Py_GIL_DISABLED
# define Py_BEGIN_CRITICAL_SECTION_MUT(mutex) \
{ \
_PyCriticalSection _cs; \
_PyCriticalSection_Begin(&_cs, mutex)
PyCriticalSection _py_cs; \
_PyCriticalSection_BeginMutex(&_py_cs, mutex)
# define Py_BEGIN_CRITICAL_SECTION(op) \
Py_BEGIN_CRITICAL_SECTION_MUT(&_PyObject_CAST(op)->ob_mutex)
# define Py_END_CRITICAL_SECTION() \
_PyCriticalSection_End(&_cs); \
}
# define Py_BEGIN_CRITICAL_SECTION2(a, b) \
# define Py_BEGIN_CRITICAL_SECTION2_MUT(m1, m2) \
{ \
_PyCriticalSection2 _cs2; \
_PyCriticalSection2_Begin(&_cs2, &_PyObject_CAST(a)->ob_mutex, &_PyObject_CAST(b)->ob_mutex)
# define Py_END_CRITICAL_SECTION2() \
_PyCriticalSection2_End(&_cs2); \
}
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*
@ -117,21 +40,21 @@ extern "C" {
{ \
PyObject *_orig_seq = _PyObject_CAST(original); \
const bool _should_lock_cs = PyList_CheckExact(_orig_seq); \
_PyCriticalSection _cs; \
PyCriticalSection _cs; \
if (_should_lock_cs) { \
_PyCriticalSection_Begin(&_cs, &_orig_seq->ob_mutex); \
_PyCriticalSection_Begin(&_cs, _orig_seq); \
}
# define Py_END_CRITICAL_SECTION_SEQUENCE_FAST() \
if (_should_lock_cs) { \
_PyCriticalSection_End(&_cs); \
PyCriticalSection_End(&_cs); \
} \
}
// Asserts that the mutex is locked. The mutex must be held by the
// top-most critical section otherwise there's the possibility
// that the mutex would be swalled out in some code paths.
#define _Py_CRITICAL_SECTION_ASSERT_MUTEX_LOCKED(mutex) \
#define _Py_CRITICAL_SECTION_ASSERT_MUTEX_LOCKED(mutex) \
_PyCriticalSection_AssertHeld(mutex)
// Asserts that the mutex for the given object is locked. The mutex must
@ -139,73 +62,57 @@ extern "C" {
// possibility that the mutex would be swalled out in some code paths.
#ifdef Py_DEBUG
#define _Py_CRITICAL_SECTION_ASSERT_OBJECT_LOCKED(op) \
# define _Py_CRITICAL_SECTION_ASSERT_OBJECT_LOCKED(op) \
if (Py_REFCNT(op) != 1) { \
_Py_CRITICAL_SECTION_ASSERT_MUTEX_LOCKED(&_PyObject_CAST(op)->ob_mutex); \
}
#else /* Py_DEBUG */
#define _Py_CRITICAL_SECTION_ASSERT_OBJECT_LOCKED(op)
# define _Py_CRITICAL_SECTION_ASSERT_OBJECT_LOCKED(op)
#endif /* Py_DEBUG */
#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_SECTION(op)
# define Py_END_CRITICAL_SECTION()
# define Py_BEGIN_CRITICAL_SECTION2(a, b)
# define Py_END_CRITICAL_SECTION2()
# define Py_BEGIN_CRITICAL_SECTION_SEQUENCE_FAST(original)
# define Py_END_CRITICAL_SECTION_SEQUENCE_FAST()
# 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)
# define _Py_CRITICAL_SECTION_ASSERT_OBJECT_LOCKED(op)
#endif /* !Py_GIL_DISABLED */
typedef struct {
// Tagged pointer to an outer active critical section (or 0).
// The two least-significant-bits indicate whether the pointed-to critical
// section is inactive and whether it is a _PyCriticalSection2 object.
uintptr_t prev;
// Mutex used to protect critical section
PyMutex *mutex;
} _PyCriticalSection;
// A critical section protected by two mutexes. Use
// _PyCriticalSection2_Begin and _PyCriticalSection2_End.
typedef struct {
_PyCriticalSection base;
PyMutex *mutex2;
} _PyCriticalSection2;
static inline int
_PyCriticalSection_IsActive(uintptr_t tag)
{
return tag != 0 && (tag & _Py_CRITICAL_SECTION_INACTIVE) == 0;
}
// Resumes the top-most critical section.
PyAPI_FUNC(void)
_PyCriticalSection_Resume(PyThreadState *tstate);
// (private) slow path for locking the mutex
PyAPI_FUNC(void)
_PyCriticalSection_BeginSlow(_PyCriticalSection *c, PyMutex *m);
_PyCriticalSection_BeginSlow(PyCriticalSection *c, PyMutex *m);
PyAPI_FUNC(void)
_PyCriticalSection2_BeginSlow(_PyCriticalSection2 *c, PyMutex *m1, PyMutex *m2,
_PyCriticalSection2_BeginSlow(PyCriticalSection2 *c, PyMutex *m1, PyMutex *m2,
int is_m1_locked);
PyAPI_FUNC(void)
_PyCriticalSection_SuspendAll(PyThreadState *tstate);
#ifdef Py_GIL_DISABLED
static inline int
_PyCriticalSection_IsActive(uintptr_t tag)
{
return tag != 0 && (tag & _Py_CRITICAL_SECTION_INACTIVE) == 0;
}
static inline void
_PyCriticalSection_Begin(_PyCriticalSection *c, PyMutex *m)
_PyCriticalSection_BeginMutex(PyCriticalSection *c, PyMutex *m)
{
if (PyMutex_LockFast(&m->_bits)) {
PyThreadState *tstate = _PyThreadState_GET();
c->mutex = m;
c->prev = tstate->critical_section;
c->_cs_mutex = m;
c->_cs_prev = tstate->critical_section;
tstate->critical_section = (uintptr_t)c;
}
else {
@ -213,14 +120,21 @@ _PyCriticalSection_Begin(_PyCriticalSection *c, PyMutex *m)
}
}
static inline void
_PyCriticalSection_Begin(PyCriticalSection *c, PyObject *op)
{
_PyCriticalSection_BeginMutex(c, &op->ob_mutex);
}
#define PyCriticalSection_Begin _PyCriticalSection_Begin
// Removes the top-most critical section from the thread's stack of critical
// sections. If the new top-most critical section is inactive, then it is
// resumed.
static inline void
_PyCriticalSection_Pop(_PyCriticalSection *c)
_PyCriticalSection_Pop(PyCriticalSection *c)
{
PyThreadState *tstate = _PyThreadState_GET();
uintptr_t prev = c->prev;
uintptr_t prev = c->_cs_prev;
tstate->critical_section = prev;
if ((prev & _Py_CRITICAL_SECTION_INACTIVE) != 0) {
@ -229,20 +143,21 @@ _PyCriticalSection_Pop(_PyCriticalSection *c)
}
static inline void
_PyCriticalSection_End(_PyCriticalSection *c)
_PyCriticalSection_End(PyCriticalSection *c)
{
PyMutex_Unlock(c->mutex);
PyMutex_Unlock(c->_cs_mutex);
_PyCriticalSection_Pop(c);
}
#define PyCriticalSection_End _PyCriticalSection_End
static inline void
_PyCriticalSection2_Begin(_PyCriticalSection2 *c, PyMutex *m1, PyMutex *m2)
_PyCriticalSection2_BeginMutex(PyCriticalSection2 *c, PyMutex *m1, PyMutex *m2)
{
if (m1 == m2) {
// If the two mutex arguments are the same, treat this as a critical
// section with a single mutex.
c->mutex2 = NULL;
_PyCriticalSection_Begin(&c->base, m1);
c->_cs_mutex2 = NULL;
_PyCriticalSection_BeginMutex(&c->_cs_base, m1);
return;
}
@ -258,9 +173,9 @@ _PyCriticalSection2_Begin(_PyCriticalSection2 *c, PyMutex *m1, PyMutex *m2)
if (PyMutex_LockFast(&m1->_bits)) {
if (PyMutex_LockFast(&m2->_bits)) {
PyThreadState *tstate = _PyThreadState_GET();
c->base.mutex = m1;
c->mutex2 = m2;
c->base.prev = tstate->critical_section;
c->_cs_base._cs_mutex = m1;
c->_cs_mutex2 = m2;
c->_cs_base._cs_prev = tstate->critical_section;
uintptr_t p = (uintptr_t)c | _Py_CRITICAL_SECTION_TWO_MUTEXES;
tstate->critical_section = p;
@ -275,19 +190,22 @@ _PyCriticalSection2_Begin(_PyCriticalSection2 *c, PyMutex *m1, PyMutex *m2)
}
static inline void
_PyCriticalSection2_End(_PyCriticalSection2 *c)
_PyCriticalSection2_Begin(PyCriticalSection2 *c, PyObject *a, PyObject *b)
{
if (c->mutex2) {
PyMutex_Unlock(c->mutex2);
}
PyMutex_Unlock(c->base.mutex);
_PyCriticalSection_Pop(&c->base);
_PyCriticalSection2_BeginMutex(c, &a->ob_mutex, &b->ob_mutex);
}
#define PyCriticalSection2_Begin _PyCriticalSection2_Begin
PyAPI_FUNC(void)
_PyCriticalSection_SuspendAll(PyThreadState *tstate);
#ifdef Py_GIL_DISABLED
static inline void
_PyCriticalSection2_End(PyCriticalSection2 *c)
{
if (c->_cs_mutex2) {
PyMutex_Unlock(c->_cs_mutex2);
}
PyMutex_Unlock(c->_cs_base._cs_mutex);
_PyCriticalSection_Pop(&c->_cs_base);
}
#define PyCriticalSection2_End _PyCriticalSection2_End
static inline void
_PyCriticalSection_AssertHeld(PyMutex *mutex)
@ -296,18 +214,18 @@ _PyCriticalSection_AssertHeld(PyMutex *mutex)
PyThreadState *tstate = _PyThreadState_GET();
uintptr_t prev = tstate->critical_section;
if (prev & _Py_CRITICAL_SECTION_TWO_MUTEXES) {
_PyCriticalSection2 *cs = (_PyCriticalSection2 *)(prev & ~_Py_CRITICAL_SECTION_MASK);
assert(cs != NULL && (cs->base.mutex == mutex || cs->mutex2 == mutex));
PyCriticalSection2 *cs = (PyCriticalSection2 *)(prev & ~_Py_CRITICAL_SECTION_MASK);
assert(cs != NULL && (cs->_cs_base._cs_mutex == mutex || cs->_cs_mutex2 == mutex));
}
else {
_PyCriticalSection *cs = (_PyCriticalSection *)(tstate->critical_section & ~_Py_CRITICAL_SECTION_MASK);
assert(cs != NULL && cs->mutex == mutex);
PyCriticalSection *cs = (PyCriticalSection *)(tstate->critical_section & ~_Py_CRITICAL_SECTION_MASK);
assert(cs != NULL && cs->_cs_mutex == mutex);
}
#endif
}
#endif
#endif /* Py_GIL_DISABLED */
#ifdef __cplusplus
}

2
Makefile.pre.in
View File

@ -1004,6 +1004,7 @@ PYTHON_HEADERS= \
$(srcdir)/Include/codecs.h \
$(srcdir)/Include/compile.h \
$(srcdir)/Include/complexobject.h \
$(srcdir)/Include/critical_section.h \
$(srcdir)/Include/descrobject.h \
$(srcdir)/Include/dictobject.h \
$(srcdir)/Include/dynamic_annotations.h \
@ -1082,6 +1083,7 @@ PYTHON_HEADERS= \
$(srcdir)/Include/cpython/compile.h \
$(srcdir)/Include/cpython/complexobject.h \
$(srcdir)/Include/cpython/context.h \
$(srcdir)/Include/cpython/critical_section.h \
$(srcdir)/Include/cpython/descrobject.h \
$(srcdir)/Include/cpython/dictobject.h \
$(srcdir)/Include/cpython/fileobject.h \

1
Misc/NEWS.d/next/C API/2024-05-21-19-41-41.gh-issue-119344.QKvzQb.rst Normal file
View File

@ -0,0 +1 @@
The critical section API is now public as part of the non-limited C API.

2
Modules/_sre/sre.c
View File

@ -2371,7 +2371,7 @@ _sre_SRE_Match_groupdict_impl(MatchObject *self, PyObject *default_value)
goto exit;
}
}
exit:
exit:;
Py_END_CRITICAL_SECTION();
return result;

13
Modules/_testcapimodule.c
View File

@ -3329,6 +3329,18 @@ function_set_warning(PyObject *Py_UNUSED(module), PyObject *Py_UNUSED(args))
Py_RETURN_NONE;
}
static PyObject *
test_critical_sections(PyObject *module, PyObject *Py_UNUSED(args))
{
Py_BEGIN_CRITICAL_SECTION(module);
Py_END_CRITICAL_SECTION();
Py_BEGIN_CRITICAL_SECTION2(module, module);
Py_END_CRITICAL_SECTION2();
Py_RETURN_NONE;
}
static PyMethodDef TestMethods[] = {
{"set_errno", set_errno, METH_VARARGS},
{"test_config", test_config, METH_NOARGS},
@ -3470,6 +3482,7 @@ static PyMethodDef TestMethods[] = {
{"check_pyimport_addmodule", check_pyimport_addmodule, METH_VARARGS},
{"test_weakref_capi", test_weakref_capi, METH_NOARGS},
{"function_set_warning", function_set_warning, METH_NOARGS},
{"test_critical_sections", test_critical_sections, METH_NOARGS},
{NULL, NULL} /* sentinel */
};

2
Objects/dictobject.c
View File

@ -3116,7 +3116,7 @@ _PyDict_FromKeys(PyObject *cls, PyObject *iterable, PyObject *value)
goto dict_iter_exit;
}
}
dict_iter_exit:
dict_iter_exit:;
Py_END_CRITICAL_SECTION();
} else {
while ((key = PyIter_Next(it)) != NULL) {

2
Objects/listobject.c
View File

@ -452,7 +452,7 @@ PyList_SetItem(PyObject *op, Py_ssize_t i,
p = self->ob_item + i;
Py_XSETREF(*p, newitem);
ret = 0;
end:
end:;
Py_END_CRITICAL_SECTION();
return ret;
}

75
Objects/typeobject.c
View File

@ -62,24 +62,13 @@ class object "PyObject *" "&PyBaseObject_Type"
// be released and reacquired during a subclass update if there's contention
// on the subclass lock.
#define TYPE_LOCK &PyInterpreterState_Get()->types.mutex
#define BEGIN_TYPE_LOCK() \
{ \
_PyCriticalSection _cs; \
_PyCriticalSection_Begin(&_cs, TYPE_LOCK); \
#define BEGIN_TYPE_LOCK() Py_BEGIN_CRITICAL_SECTION_MUT(TYPE_LOCK)
#define END_TYPE_LOCK() Py_END_CRITICAL_SECTION()
#define END_TYPE_LOCK() \
_PyCriticalSection_End(&_cs); \
}
#define BEGIN_TYPE_DICT_LOCK(d) \
Py_BEGIN_CRITICAL_SECTION2_MUT(TYPE_LOCK, &_PyObject_CAST(d)->ob_mutex)
#define BEGIN_TYPE_DICT_LOCK(d) \
{ \
_PyCriticalSection2 _cs; \
_PyCriticalSection2_Begin(&_cs, TYPE_LOCK, \
&_PyObject_CAST(d)->ob_mutex); \
#define END_TYPE_DICT_LOCK() \
_PyCriticalSection2_End(&_cs); \
}
#define END_TYPE_DICT_LOCK() Py_END_CRITICAL_SECTION2()
#define ASSERT_TYPE_LOCK_HELD() \
_Py_CRITICAL_SECTION_ASSERT_MUTEX_LOCKED(TYPE_LOCK)
@ -442,7 +431,7 @@ _PyType_GetBases(PyTypeObject *self)
BEGIN_TYPE_LOCK();
res = lookup_tp_bases(self);
Py_INCREF(res);
END_TYPE_LOCK()
END_TYPE_LOCK();
return res;
}
@ -513,7 +502,7 @@ _PyType_GetMRO(PyTypeObject *self)
BEGIN_TYPE_LOCK();
mro = lookup_tp_mro(self);
Py_XINCREF(mro);
END_TYPE_LOCK()
END_TYPE_LOCK();
return mro;
#else
return Py_XNewRef(lookup_tp_mro(self));
@ -951,10 +940,10 @@ PyType_Watch(int watcher_id, PyObject* obj)
return -1;
}
// ensure we will get a callback on the next modification
BEGIN_TYPE_LOCK()
BEGIN_TYPE_LOCK();
assign_version_tag(interp, type);
type->tp_watched |= (1 << watcher_id);
END_TYPE_LOCK()
END_TYPE_LOCK();
return 0;
}
@ -1080,9 +1069,9 @@ PyType_Modified(PyTypeObject *type)
return;
}
BEGIN_TYPE_LOCK()
BEGIN_TYPE_LOCK();
type_modified_unlocked(type);
END_TYPE_LOCK()
END_TYPE_LOCK();
}
static int
@ -1161,9 +1150,9 @@ void
_PyType_SetVersion(PyTypeObject *tp, unsigned int version)
{
BEGIN_TYPE_LOCK()
BEGIN_TYPE_LOCK();
set_version_unlocked(tp, version);
END_TYPE_LOCK()
END_TYPE_LOCK();
}
PyTypeObject *
@ -1245,9 +1234,9 @@ int PyUnstable_Type_AssignVersionTag(PyTypeObject *type)
{
PyInterpreterState *interp = _PyInterpreterState_GET();
int assigned;
BEGIN_TYPE_LOCK()
BEGIN_TYPE_LOCK();
assigned = assign_version_tag(interp, type);
END_TYPE_LOCK()
END_TYPE_LOCK();
return assigned;
}
@ -1532,7 +1521,7 @@ type_get_mro(PyTypeObject *type, void *context)
{
PyObject *mro;
BEGIN_TYPE_LOCK()
BEGIN_TYPE_LOCK();
mro = lookup_tp_mro(type);
if (mro == NULL) {
mro = Py_None;
@ -1540,7 +1529,7 @@ type_get_mro(PyTypeObject *type, void *context)
Py_INCREF(mro);
}
END_TYPE_LOCK()
END_TYPE_LOCK();
return mro;
}
@ -3121,9 +3110,9 @@ static PyObject *
mro_implementation(PyTypeObject *type)
{
PyObject *mro;
BEGIN_TYPE_LOCK()
BEGIN_TYPE_LOCK();
mro = mro_implementation_unlocked(type);
END_TYPE_LOCK()
END_TYPE_LOCK();
return mro;
}
@ -3310,9 +3299,9 @@ static int
mro_internal(PyTypeObject *type, PyObject **p_old_mro)
{
int res;
BEGIN_TYPE_LOCK()
BEGIN_TYPE_LOCK();
res = mro_internal_unlocked(type, 0, p_old_mro);
END_TYPE_LOCK()
END_TYPE_LOCK();
return res;
}
@ -5173,7 +5162,7 @@ get_module_by_def(PyTypeObject *type, PyModuleDef *def)
}
PyObject *res = NULL;
BEGIN_TYPE_LOCK()
BEGIN_TYPE_LOCK();
PyObject *mro = lookup_tp_mro(type);
// The type must be ready
@ -5200,7 +5189,7 @@ get_module_by_def(PyTypeObject *type, PyModuleDef *def)
break;
}
}
END_TYPE_LOCK()
END_TYPE_LOCK();
return res;
}
@ -5458,13 +5447,13 @@ _PyType_LookupRef(PyTypeObject *type, PyObject *name)
int has_version = 0;
int version = 0;
BEGIN_TYPE_LOCK()
BEGIN_TYPE_LOCK();
res = find_name_in_mro(type, name, &error);
if (MCACHE_CACHEABLE_NAME(name)) {
has_version = assign_version_tag(interp, type);
version = type->tp_version_tag;
}
END_TYPE_LOCK()
END_TYPE_LOCK();
/* Only put NULL results into cache if there was no error. */
if (error) {
@ -8454,14 +8443,14 @@ PyType_Ready(PyTypeObject *type)
}
int res;
BEGIN_TYPE_LOCK()
BEGIN_TYPE_LOCK();
if (!(type->tp_flags & Py_TPFLAGS_READY)) {
res = type_ready(type, 1);
} else {
res = 0;
assert(_PyType_CheckConsistency(type));
}
END_TYPE_LOCK()
END_TYPE_LOCK();
return res;
}
@ -8495,7 +8484,7 @@ init_static_type(PyInterpreterState *interp, PyTypeObject *self,
int res;
BEGIN_TYPE_LOCK();
res = type_ready(self, initial);
END_TYPE_LOCK()
END_TYPE_LOCK();
if (res < 0) {
_PyStaticType_ClearWeakRefs(interp, self);
managed_static_type_state_clear(interp, self, isbuiltin, initial);
@ -8967,7 +8956,7 @@ hackcheck(PyObject *self, setattrofunc func, const char *what)
int res;
BEGIN_TYPE_LOCK();
res = hackcheck_unlocked(self, func, what);
END_TYPE_LOCK()
END_TYPE_LOCK();
return res;
}
@ -10896,14 +10885,14 @@ fixup_slot_dispatchers(PyTypeObject *type)
// This lock isn't strictly necessary because the type has not been
// exposed to anyone else yet, but update_ont_slot calls find_name_in_mro
// where we'd like to assert that the type is locked.
BEGIN_TYPE_LOCK()
BEGIN_TYPE_LOCK();
assert(!PyErr_Occurred());
for (pytype_slotdef *p = slotdefs; p->name; ) {
p = update_one_slot(type, p);
}
END_TYPE_LOCK()
END_TYPE_LOCK();
}
static void
@ -11192,7 +11181,7 @@ _super_lookup_descr(PyTypeObject *su_type, PyTypeObject *su_obj_type, PyObject *
another thread can modify it after we end the critical section
below */
Py_XINCREF(mro);
END_TYPE_LOCK()
END_TYPE_LOCK();
if (mro == NULL)
return NULL;

2
PCbuild/pythoncore.vcxproj
View File

@ -135,6 +135,7 @@
<ClInclude Include="..\Include\codecs.h" />
<ClInclude Include="..\Include\compile.h" />
<ClInclude Include="..\Include\complexobject.h" />
<ClInclude Include="..\Include\critical_section.h" />
<ClInclude Include="..\Include\cpython\abstract.h" />
<ClInclude Include="..\Include\cpython\bytearrayobject.h" />
<ClInclude Include="..\Include\cpython\bytesobject.h" />
@ -145,6 +146,7 @@
<ClInclude Include="..\Include\cpython\compile.h" />
<ClInclude Include="..\Include\cpython\complexobject.h" />
<ClInclude Include="..\Include\cpython\context.h" />
<ClInclude Include="..\Include\cpython\critical_section.h" />
<ClInclude Include="..\Include\cpython\descrobject.h" />
<ClInclude Include="..\Include\cpython\dictobject.h" />
<ClInclude Include="..\Include\cpython\fileobject.h" />

6
PCbuild/pythoncore.vcxproj.filters
View File

@ -72,6 +72,9 @@
<ClInclude Include="..\Include\complexobject.h">
<Filter>Include</Filter>
</ClInclude>
<ClInclude Include="..\Include\critical_section.h">
<Filter>Include</Filter>
</ClInclude>
<ClInclude Include="..\Include\datetime.h">
<Filter>Include</Filter>
</ClInclude>
@ -378,6 +381,9 @@
<ClInclude Include="..\Include\cpython\context.h">
<Filter>Include\cpython</Filter>
</ClInclude>
<ClInclude Include="..\Include\cpython\critical_section.h">
<Filter>Include\cpython</Filter>
</ClInclude>
<ClInclude Include="..\Include\cpython\descrobject.h">
<Filter>Include\cpython</Filter>
</ClInclude>

106
Python/critical_section.c
View File

@ -3,85 +3,96 @@
#include "pycore_lock.h"
#include "pycore_critical_section.h"
static_assert(_Alignof(_PyCriticalSection) >= 4,
#ifdef Py_GIL_DISABLED
static_assert(_Alignof(PyCriticalSection) >= 4,
"critical section must be aligned to at least 4 bytes");
#endif
void
_PyCriticalSection_BeginSlow(_PyCriticalSection *c, PyMutex *m)
_PyCriticalSection_BeginSlow(PyCriticalSection *c, PyMutex *m)
{
#ifdef Py_GIL_DISABLED
PyThreadState *tstate = _PyThreadState_GET();
c->mutex = NULL;
c->prev = (uintptr_t)tstate->critical_section;
c->_cs_mutex = NULL;
c->_cs_prev = (uintptr_t)tstate->critical_section;
tstate->critical_section = (uintptr_t)c;
PyMutex_Lock(m);
c->mutex = m;
c->_cs_mutex = m;
#endif
}
void
_PyCriticalSection2_BeginSlow(_PyCriticalSection2 *c, PyMutex *m1, PyMutex *m2,
_PyCriticalSection2_BeginSlow(PyCriticalSection2 *c, PyMutex *m1, PyMutex *m2,
int is_m1_locked)
{
#ifdef Py_GIL_DISABLED
PyThreadState *tstate = _PyThreadState_GET();
c->base.mutex = NULL;
c->mutex2 = NULL;
c->base.prev = tstate->critical_section;
c->_cs_base._cs_mutex = NULL;
c->_cs_mutex2 = NULL;
c->_cs_base._cs_prev = tstate->critical_section;
tstate->critical_section = (uintptr_t)c | _Py_CRITICAL_SECTION_TWO_MUTEXES;
if (!is_m1_locked) {
PyMutex_Lock(m1);
}
PyMutex_Lock(m2);
c->base.mutex = m1;
c->mutex2 = m2;
c->_cs_base._cs_mutex = m1;
c->_cs_mutex2 = m2;
#endif
}
static _PyCriticalSection *
#ifdef Py_GIL_DISABLED
static PyCriticalSection *
untag_critical_section(uintptr_t tag)
{
return (_PyCriticalSection *)(tag & ~_Py_CRITICAL_SECTION_MASK);
return (PyCriticalSection *)(tag & ~_Py_CRITICAL_SECTION_MASK);
}
#endif
// Release all locks held by critical sections. This is called by
// _PyThreadState_Detach.
void
_PyCriticalSection_SuspendAll(PyThreadState *tstate)
{
#ifdef Py_GIL_DISABLED
uintptr_t *tagptr = &tstate->critical_section;
while (_PyCriticalSection_IsActive(*tagptr)) {
_PyCriticalSection *c = untag_critical_section(*tagptr);
PyCriticalSection *c = untag_critical_section(*tagptr);
if (c->mutex) {
PyMutex_Unlock(c->mutex);
if (c->_cs_mutex) {
PyMutex_Unlock(c->_cs_mutex);
if ((*tagptr & _Py_CRITICAL_SECTION_TWO_MUTEXES)) {
_PyCriticalSection2 *c2 = (_PyCriticalSection2 *)c;
if (c2->mutex2) {
PyMutex_Unlock(c2->mutex2);
PyCriticalSection2 *c2 = (PyCriticalSection2 *)c;
if (c2->_cs_mutex2) {
PyMutex_Unlock(c2->_cs_mutex2);
}
}
}
*tagptr |= _Py_CRITICAL_SECTION_INACTIVE;
tagptr = &c->prev;
tagptr = &c->_cs_prev;
}
#endif
}
void
_PyCriticalSection_Resume(PyThreadState *tstate)
{
#ifdef Py_GIL_DISABLED
uintptr_t p = tstate->critical_section;
_PyCriticalSection *c = untag_critical_section(p);
PyCriticalSection *c = untag_critical_section(p);
assert(!_PyCriticalSection_IsActive(p));
PyMutex *m1 = c->mutex;
c->mutex = NULL;
PyMutex *m1 = c->_cs_mutex;
c->_cs_mutex = NULL;
PyMutex *m2 = NULL;
_PyCriticalSection2 *c2 = NULL;
PyCriticalSection2 *c2 = NULL;
if ((p & _Py_CRITICAL_SECTION_TWO_MUTEXES)) {
c2 = (_PyCriticalSection2 *)c;
m2 = c2->mutex2;
c2->mutex2 = NULL;
c2 = (PyCriticalSection2 *)c;
m2 = c2->_cs_mutex2;
c2->_cs_mutex2 = NULL;
}
if (m1) {
@ -91,10 +102,47 @@ _PyCriticalSection_Resume(PyThreadState *tstate)
PyMutex_Lock(m2);
}
c->mutex = m1;
c->_cs_mutex = m1;
if (m2) {
c2->mutex2 = m2;
c2->_cs_mutex2 = m2;
}
tstate->critical_section &= ~_Py_CRITICAL_SECTION_INACTIVE;
#endif
}
#undef PyCriticalSection_Begin
void
PyCriticalSection_Begin(PyCriticalSection *c, PyObject *op)
{
#ifdef Py_GIL_DISABLED
_PyCriticalSection_Begin(c, op);
#endif
}
#undef PyCriticalSection_End
void
PyCriticalSection_End(PyCriticalSection *c)
{
#ifdef Py_GIL_DISABLED
_PyCriticalSection_End(c);
#endif
}
#undef PyCriticalSection2_Begin
void
PyCriticalSection2_Begin(PyCriticalSection2 *c, PyObject *a, PyObject *b)
{
#ifdef Py_GIL_DISABLED
_PyCriticalSection2_Begin(c, a, b);
#endif
}
#undef PyCriticalSection2_End
void
PyCriticalSection2_End(PyCriticalSection2 *c)
{
#ifdef Py_GIL_DISABLED
_PyCriticalSection2_End(c);
#endif
}