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gh-148393: Use acquire load for _ma_watcher_tag in dict notify event (gh-148509)

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The watcher-bits read in _PyDict_NotifyEvent needs to use acquire to
synchronize with the release from PyDict_Watch so that the callback
publication is visible before the callback is invoked.
This commit is contained in:
Sam Gross 2026-04-13 14:11:28 -04:00 • committed by GitHub
parent e6893943b7
commit 19f96f99fe
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GPG key ID: B5690EEEBB952194
2 changed files with 4 additions and 1 deletions
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2
Include/internal/pycore_dict.h
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@ -292,7 +292,7 @@ _PyDict_NotifyEvent(PyDict_WatchEvent event,
PyObject *value)
{
assert(Py_REFCNT((PyObject*)mp) > 0);
int watcher_bits = FT_ATOMIC_LOAD_UINT64_RELAXED(mp->_ma_watcher_tag) & DICT_WATCHER_MASK;
int watcher_bits = FT_ATOMIC_LOAD_UINT64_ACQUIRE(mp->_ma_watcher_tag) & DICT_WATCHER_MASK;
if (watcher_bits) {
RARE_EVENT_STAT_INC(watched_dict_modification);
_PyDict_SendEvent(watcher_bits, event, mp, key, value);

3
Include/internal/pycore_pyatomic_ft_wrappers.h
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@ -49,6 +49,8 @@ extern "C" {
_Py_atomic_load_uint16_relaxed(&value)
#define FT_ATOMIC_LOAD_UINT32_RELAXED(value) \
_Py_atomic_load_uint32_relaxed(&value)
#define FT_ATOMIC_LOAD_UINT64_ACQUIRE(value) \
_Py_atomic_load_uint64_acquire(&value)
#define FT_ATOMIC_LOAD_UINT64_RELAXED(value) \
_Py_atomic_load_uint64_relaxed(&value)
#define FT_ATOMIC_LOAD_ULONG_RELAXED(value) \
@ -154,6 +156,7 @@ extern "C" {
#define FT_ATOMIC_LOAD_UINT8_RELAXED(value) value
#define FT_ATOMIC_LOAD_UINT16_RELAXED(value) value
#define FT_ATOMIC_LOAD_UINT32_RELAXED(value) value
#define FT_ATOMIC_LOAD_UINT64_ACQUIRE(value) value
#define FT_ATOMIC_LOAD_UINT64_RELAXED(value) value
#define FT_ATOMIC_LOAD_ULONG_RELAXED(value) value
#define FT_ATOMIC_STORE_PTR_RELAXED(value, new_value) value = new_value