* :c:func:`PyMem_RawCalloc`
* :c:func:`PyMem_RawFree`
+* Synchronization:
+
+ * :c:func:`PyMutex_Lock`
+ * :c:func:`PyMutex_Unlock`
+
.. note::
The following functions **should not be called** before
.. c:function:: void PyThread_delete_key_value(int key)
.. c:function:: void PyThread_ReInitTLS()
+Synchronization Primitives
+==========================
+
+The C-API provides a basic mutual exclusion lock.
+
+.. c:type:: PyMutex
+
+ A mutual exclusion lock. The :c:type:`!PyMutex` should be initialized to
+ zero to represent the unlocked state. For example::
+
+ PyMutex mutex = {0};
+
+ Instances of :c:type:`!PyMutex` should not be copied or moved. Both the
+ contents and address of a :c:type:`!PyMutex` are meaningful, and it must
+ remain at a fixed, writable location in memory.
+
+ .. note::
+
+ A :c:type:`!PyMutex` currently occupies one byte, but the size should be
+ considered unstable. The size may change in future Python releases
+ without a deprecation period.
+
+ .. versionadded:: 3.13
+
+.. c:function:: void PyMutex_Lock(PyMutex *m)
+
+ Lock mutex *m*. If another thread has already locked it, the calling
+ thread will block until the mutex is unlocked. While blocked, the thread
+ will temporarily release the :term:`GIL` if it is held.
+
+ .. versionadded:: 3.13
+
+.. c:function:: void PyMutex_Unlock(PyMutex *m)
+
+ Unlock mutex *m*. The mutex must be locked --- otherwise, the function will
+ issue a fatal error.
+
+ .. versionadded:: 3.13
:c:func:`PyEval_GetLocals` return :term:`strong references <strong reference>`
rather than borrowed references. (Added as part of :pep:`667`.)
+* Add :c:type:`PyMutex` API, a lightweight mutex that occupies a single byte.
+ The :c:func:`PyMutex_Lock` function will release the GIL (if currently held)
+ if the operation needs to block.
+ (Contributed by Sam Gross in :gh:`108724`.)
+
Build Changes
=============
#include "pybuffer.h"
#include "pystats.h"
#include "pyatomic.h"
+#include "lock.h"
#include "object.h"
#include "refcount.h"
#include "objimpl.h"
--- /dev/null
+#ifndef Py_CPYTHON_LOCK_H
+# error "this header file must not be included directly"
+#endif
+
+#define _Py_UNLOCKED 0
+#define _Py_LOCKED 1
+
+// A mutex that occupies one byte. The lock can be zero initialized to
+// represent the unlocked state.
+//
+// Typical initialization:
+// PyMutex m = (PyMutex){0};
+//
+// Or initialize as global variables:
+// static PyMutex m;
+//
+// Typical usage:
+// PyMutex_Lock(&m);
+// ...
+// PyMutex_Unlock(&m);
+//
+// The contents of the PyMutex are not part of the public API, but are
+// described to aid in understanding the implementation and debugging. Only
+// the two least significant bits are used. The remaining bits are always zero:
+// 0b00: unlocked
+// 0b01: locked
+// 0b10: unlocked and has parked threads
+// 0b11: locked and has parked threads
+typedef struct PyMutex {
+ uint8_t _bits; // (private)
+} PyMutex;
+
+// exported function for locking the mutex
+PyAPI_FUNC(void) PyMutex_Lock(PyMutex *m);
+
+// exported function for unlocking the mutex
+PyAPI_FUNC(void) PyMutex_Unlock(PyMutex *m);
+
+// Locks the mutex.
+//
+// If the mutex is currently locked, the calling thread will be parked until
+// the mutex is unlocked. If the current thread holds the GIL, then the GIL
+// will be released while the thread is parked.
+static inline void
+_PyMutex_Lock(PyMutex *m)
+{
+ uint8_t expected = _Py_UNLOCKED;
+ if (!_Py_atomic_compare_exchange_uint8(&m->_bits, &expected, _Py_LOCKED)) {
+ PyMutex_Lock(m);
+ }
+}
+#define PyMutex_Lock _PyMutex_Lock
+
+// Unlocks the mutex.
+static inline void
+_PyMutex_Unlock(PyMutex *m)
+{
+ uint8_t expected = _Py_LOCKED;
+ if (!_Py_atomic_compare_exchange_uint8(&m->_bits, &expected, _Py_UNLOCKED)) {
+ PyMutex_Unlock(m);
+ }
+}
+#define PyMutex_Unlock _PyMutex_Unlock
* Normally this can be derived from wr_object, but in some cases we need
* to lock after wr_object has been set to Py_None.
*/
- struct _PyMutex *weakrefs_lock;
+ PyMutex *weakrefs_lock;
#endif
};
static inline void
_PyCriticalSection_Begin(_PyCriticalSection *c, PyMutex *m)
{
- if (PyMutex_LockFast(&m->v)) {
+ if (PyMutex_LockFast(&m->_bits)) {
PyThreadState *tstate = _PyThreadState_GET();
c->mutex = m;
c->prev = tstate->critical_section;
m2 = tmp;
}
- if (PyMutex_LockFast(&m1->v)) {
- if (PyMutex_LockFast(&m2->v)) {
+ if (PyMutex_LockFast(&m1->_bits)) {
+ if (PyMutex_LockFast(&m2->_bits)) {
PyThreadState *tstate = _PyThreadState_GET();
c->base.mutex = m1;
c->mutex2 = m2;
# error "this header requires Py_BUILD_CORE define"
#endif
-
-// A mutex that occupies one byte. The lock can be zero initialized.
-//
-// Only the two least significant bits are used. The remaining bits should be
-// zero:
-// 0b00: unlocked
-// 0b01: locked
-// 0b10: unlocked and has parked threads
-// 0b11: locked and has parked threads
-//
-// Typical initialization:
-// PyMutex m = (PyMutex){0};
-//
-// Or initialize as global variables:
-// static PyMutex m;
-//
-// Typical usage:
-// PyMutex_Lock(&m);
-// ...
-// PyMutex_Unlock(&m);
-
-// NOTE: In Py_GIL_DISABLED builds, `struct _PyMutex` is defined in Include/object.h.
-// The Py_GIL_DISABLED builds need the definition in Include/object.h for the
-// `ob_mutex` field in PyObject. For the default (non-free-threaded) build,
-// we define the struct here to avoid exposing it in the public API.
-#ifndef Py_GIL_DISABLED
-struct _PyMutex { uint8_t v; };
-#endif
-
-typedef struct _PyMutex PyMutex;
-
-#define _Py_UNLOCKED 0
-#define _Py_LOCKED 1
+//_Py_UNLOCKED is defined as 0 and _Py_LOCKED as 1 in Include/cpython/lock.h
#define _Py_HAS_PARKED 2
#define _Py_ONCE_INITIALIZED 4
-// (private) slow path for locking the mutex
-PyAPI_FUNC(void) _PyMutex_LockSlow(PyMutex *m);
-
-// (private) slow path for unlocking the mutex
-PyAPI_FUNC(void) _PyMutex_UnlockSlow(PyMutex *m);
-
static inline int
PyMutex_LockFast(uint8_t *lock_bits)
{
return _Py_atomic_compare_exchange_uint8(lock_bits, &expected, _Py_LOCKED);
}
-// Locks the mutex.
-//
-// If the mutex is currently locked, the calling thread will be parked until
-// the mutex is unlocked. If the current thread holds the GIL, then the GIL
-// will be released while the thread is parked.
-static inline void
-PyMutex_Lock(PyMutex *m)
-{
- uint8_t expected = _Py_UNLOCKED;
- if (!_Py_atomic_compare_exchange_uint8(&m->v, &expected, _Py_LOCKED)) {
- _PyMutex_LockSlow(m);
- }
-}
-
-// Unlocks the mutex.
-static inline void
-PyMutex_Unlock(PyMutex *m)
-{
- uint8_t expected = _Py_LOCKED;
- if (!_Py_atomic_compare_exchange_uint8(&m->v, &expected, _Py_UNLOCKED)) {
- _PyMutex_UnlockSlow(m);
- }
-}
-
// Checks if the mutex is currently locked.
static inline int
PyMutex_IsLocked(PyMutex *m)
{
- return (_Py_atomic_load_uint8(&m->v) & _Py_LOCKED) != 0;
+ return (_Py_atomic_load_uint8(&m->_bits) & _Py_LOCKED) != 0;
}
// Re-initializes the mutex after a fork to the unlocked state.
PyMutex_LockFlags(PyMutex *m, _PyLockFlags flags)
{
uint8_t expected = _Py_UNLOCKED;
- if (!_Py_atomic_compare_exchange_uint8(&m->v, &expected, _Py_LOCKED)) {
+ if (!_Py_atomic_compare_exchange_uint8(&m->_bits, &expected, _Py_LOCKED)) {
_PyMutex_LockTimed(m, -1, flags);
}
}
PyObject *filters; /* List */
PyObject *once_registry; /* Dict */
PyObject *default_action; /* String */
- struct _PyMutex mutex;
+ PyMutex mutex;
long filters_version;
};
--- /dev/null
+#ifndef Py_LOCK_H
+#define Py_LOCK_H
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+#ifndef Py_LIMITED_API
+# define Py_CPYTHON_LOCK_H
+# include "cpython/lock.h"
+# undef Py_CPYTHON_LOCK_H
+#endif
+
+#ifdef __cplusplus
+}
+#endif
+#endif /* !Py_LOCK_H */
// fields have been merged.
#define _Py_UNOWNED_TID 0
-// NOTE: In non-free-threaded builds, `struct _PyMutex` is defined in
-// pycore_lock.h. See pycore_lock.h for more details.
-struct _PyMutex { uint8_t v; };
-
struct _object {
// ob_tid stores the thread id (or zero). It is also used by the GC and the
// trashcan mechanism as a linked list pointer and by the GC to store the
// computed "gc_refs" refcount.
uintptr_t ob_tid;
uint16_t _padding;
- struct _PyMutex ob_mutex; // per-object lock
+ PyMutex ob_mutex; // per-object lock
uint8_t ob_gc_bits; // gc-related state
uint32_t ob_ref_local; // local reference count
Py_ssize_t ob_ref_shared; // shared (atomic) reference count
$(srcdir)/Include/intrcheck.h \
$(srcdir)/Include/iterobject.h \
$(srcdir)/Include/listobject.h \
+ $(srcdir)/Include/lock.h \
$(srcdir)/Include/longobject.h \
$(srcdir)/Include/marshal.h \
$(srcdir)/Include/memoryobject.h \
$(srcdir)/Include/cpython/import.h \
$(srcdir)/Include/cpython/initconfig.h \
$(srcdir)/Include/cpython/listobject.h \
+ $(srcdir)/Include/cpython/lock.h \
$(srcdir)/Include/cpython/longintrepr.h \
$(srcdir)/Include/cpython/longobject.h \
$(srcdir)/Include/cpython/memoryobject.h \
--- /dev/null
+Make the :c:type:`PyMutex` public in the non-limited C API.
// uncontended lock and unlock
PyMutex_Lock(&m);
- assert(m.v == 1);
+ assert(m._bits == 1);
PyMutex_Unlock(&m);
- assert(m.v == 0);
+ assert(m._bits == 0);
Py_RETURN_NONE;
}
_Py_atomic_store_int(&test_data->started, 1);
PyMutex_Lock(m);
- assert(m->v == 1);
+ assert(m->_bits == 1);
PyMutex_Unlock(m);
- assert(m->v == 0);
+ assert(m->_bits == 0);
_PyEvent_Notify(&test_data->done);
}
memset(&test_data, 0, sizeof(test_data));
PyMutex_Lock(&test_data.m);
- assert(test_data.m.v == 1);
+ assert(test_data.m._bits == 1);
PyThread_start_new_thread(lock_thread, &test_data);
uint8_t v;
do {
pysleep(10); // allow some time for the other thread to try to lock
- v = _Py_atomic_load_uint8_relaxed(&test_data.m.v);
+ v = _Py_atomic_load_uint8_relaxed(&test_data.m._bits);
assert(v == 1 || v == 3);
iters++;
} while (v != 3 && iters < 200);
// both the "locked" and the "has parked" bits should be set
- assert(test_data.m.v == 3);
+ assert(test_data.m._bits == 3);
PyMutex_Unlock(&test_data.m);
PyEvent_Wait(&test_data.done);
- assert(test_data.m.v == 0);
+ assert(test_data.m._bits == 0);
Py_RETURN_NONE;
}
#else
op->ob_tid = _Py_ThreadId();
op->_padding = 0;
- op->ob_mutex = (struct _PyMutex){ 0 };
+ op->ob_mutex = (PyMutex){ 0 };
op->ob_gc_bits = 0;
op->ob_ref_local = 1;
op->ob_ref_shared = 0;
<ClInclude Include="..\Include\cpython\import.h" />
<ClInclude Include="..\Include\cpython\initconfig.h" />
<ClInclude Include="..\Include\cpython\listobject.h" />
+ <ClInclude Include="..\Include\cpython\lock.h" />
<ClInclude Include="..\Include\cpython\longintrepr.h" />
<ClInclude Include="..\Include\cpython\longobject.h" />
<ClInclude Include="..\Include\cpython\memoryobject.h" />
<ClInclude Include="..\Include\intrcheck.h" />
<ClInclude Include="..\Include\iterobject.h" />
<ClInclude Include="..\Include\listobject.h" />
+ <ClInclude Include="..\Include\lock.h" />
<ClInclude Include="..\Include\longobject.h" />
<ClInclude Include="..\Include\marshal.h" />
<ClInclude Include="..\Include\memoryobject.h" />
<ClInclude Include="..\Include\listobject.h">
<Filter>Include</Filter>
</ClInclude>
+ <ClInclude Include="..\Include\lock.h">
+ <Filter>Include</Filter>
+ </ClInclude>
<ClInclude Include="..\Include\longobject.h">
<Filter>Include</Filter>
</ClInclude>
<ClInclude Include="..\Include\cpython\listobject.h">
<Filter>Include\cpython</Filter>
</ClInclude>
+ <ClInclude Include="..\Include\cpython\lock.h">
+ <Filter>Include</Filter>
+ </ClInclude>
<ClInclude Include="..\Include\cpython\longintrepr.h">
<Filter>Include</Filter>
</ClInclude>
c->prev = (uintptr_t)tstate->critical_section;
tstate->critical_section = (uintptr_t)c;
- _PyMutex_LockSlow(m);
+ PyMutex_Lock(m);
c->mutex = m;
}
#endif
}
-void
-_PyMutex_LockSlow(PyMutex *m)
-{
- _PyMutex_LockTimed(m, -1, _PY_LOCK_DETACH);
-}
-
PyLockStatus
_PyMutex_LockTimed(PyMutex *m, PyTime_t timeout, _PyLockFlags flags)
{
- uint8_t v = _Py_atomic_load_uint8_relaxed(&m->v);
+ uint8_t v = _Py_atomic_load_uint8_relaxed(&m->_bits);
if ((v & _Py_LOCKED) == 0) {
- if (_Py_atomic_compare_exchange_uint8(&m->v, &v, v|_Py_LOCKED)) {
+ if (_Py_atomic_compare_exchange_uint8(&m->_bits, &v, v|_Py_LOCKED)) {
return PY_LOCK_ACQUIRED;
}
}
for (;;) {
if ((v & _Py_LOCKED) == 0) {
// The lock is unlocked. Try to grab it.
- if (_Py_atomic_compare_exchange_uint8(&m->v, &v, v|_Py_LOCKED)) {
+ if (_Py_atomic_compare_exchange_uint8(&m->_bits, &v, v|_Py_LOCKED)) {
return PY_LOCK_ACQUIRED;
}
continue;
if (!(v & _Py_HAS_PARKED)) {
// We are the first waiter. Set the _Py_HAS_PARKED flag.
newv = v | _Py_HAS_PARKED;
- if (!_Py_atomic_compare_exchange_uint8(&m->v, &v, newv)) {
+ if (!_Py_atomic_compare_exchange_uint8(&m->_bits, &v, newv)) {
continue;
}
}
- int ret = _PyParkingLot_Park(&m->v, &newv, sizeof(newv), timeout,
+ int ret = _PyParkingLot_Park(&m->_bits, &newv, sizeof(newv), timeout,
&entry, (flags & _PY_LOCK_DETACH) != 0);
if (ret == Py_PARK_OK) {
if (entry.handed_off) {
// We own the lock now.
- assert(_Py_atomic_load_uint8_relaxed(&m->v) & _Py_LOCKED);
+ assert(_Py_atomic_load_uint8_relaxed(&m->_bits) & _Py_LOCKED);
return PY_LOCK_ACQUIRED;
}
}
}
}
- v = _Py_atomic_load_uint8_relaxed(&m->v);
+ v = _Py_atomic_load_uint8_relaxed(&m->_bits);
}
}
v |= _Py_HAS_PARKED;
}
}
- _Py_atomic_store_uint8(&m->v, v);
+ _Py_atomic_store_uint8(&m->_bits, v);
}
int
_PyMutex_TryUnlock(PyMutex *m)
{
- uint8_t v = _Py_atomic_load_uint8(&m->v);
+ uint8_t v = _Py_atomic_load_uint8(&m->_bits);
for (;;) {
if ((v & _Py_LOCKED) == 0) {
// error: the mutex is not locked
}
else if ((v & _Py_HAS_PARKED)) {
// wake up a single thread
- _PyParkingLot_Unpark(&m->v, (_Py_unpark_fn_t *)mutex_unpark, m);
+ _PyParkingLot_Unpark(&m->_bits, (_Py_unpark_fn_t *)mutex_unpark, m);
return 0;
}
- else if (_Py_atomic_compare_exchange_uint8(&m->v, &v, _Py_UNLOCKED)) {
+ else if (_Py_atomic_compare_exchange_uint8(&m->_bits, &v, _Py_UNLOCKED)) {
// fast-path: no waiters
return 0;
}
}
}
-void
-_PyMutex_UnlockSlow(PyMutex *m)
-{
- if (_PyMutex_TryUnlock(m) < 0) {
- Py_FatalError("unlocking mutex that is not locked");
- }
-}
-
// _PyRawMutex stores a linked list of `struct raw_mutex_entry`, one for each
// thread waiting on the mutex, directly in the mutex itself.
struct raw_mutex_entry {
return 0;
}
+
+#undef PyMutex_Lock
+void
+PyMutex_Lock(PyMutex *m)
+{
+ _PyMutex_LockTimed(m, -1, _PY_LOCK_DETACH);
+}
+
+#undef PyMutex_Unlock
+void
+PyMutex_Unlock(PyMutex *m)
+{
+ if (_PyMutex_TryUnlock(m) < 0) {
+ Py_FatalError("unlocking mutex that is not locked");
+ }
+}
projects / thirdparty / Python / cpython.git / commitdiff
