https://github.com/python/cpython/commit/19f96f99febe9eadbcc58ffc042791fb017ac90b
commit: 19f96f99febe9eadbcc58ffc042791fb017ac90b
branch: main
author: Sam Gross <[email protected]>
committer: colesbury <[email protected]>
date: 2026-04-13T14:11:28-04:00
summary:
gh-148393: Use acquire load for _ma_watcher_tag in dict notify event (gh-148509)
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.
files:
M Include/internal/pycore_dict.h
M Include/internal/pycore_pyatomic_ft_wrappers.h
diff --git a/Include/internal/pycore_dict.h b/Include/internal/pycore_dict.h
index 5bbea187394db6..68d353b213c097 100644
--- a/Include/internal/pycore_dict.h
+++ b/Include/internal/pycore_dict.h
@@ -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);
diff --git a/Include/internal/pycore_pyatomic_ft_wrappers.h
b/Include/internal/pycore_pyatomic_ft_wrappers.h
index 3155481bb5c36b..fafdd728a8229a 100644
--- a/Include/internal/pycore_pyatomic_ft_wrappers.h
+++ b/Include/internal/pycore_pyatomic_ft_wrappers.h
@@ -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
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