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gh-112075: Dictionary global version counter should use atomic increments #114568

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Merged
merged 1 commit into from
Jan 29, 2024
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gh-112075: Dictionary global version counter should use atomic increments #114568

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6 changes: 6 additions & 0 deletions 6 Include/internal/pycore_dict.h
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Original file line number Diff line number Diff line change
Expand Up @@ -209,8 +209,14 @@ static inline PyDictUnicodeEntry* DK_UNICODE_ENTRIES(PyDictKeysObject *dk) {
#define DICT_VERSION_INCREMENT (1 << DICT_MAX_WATCHERS)
#define DICT_VERSION_MASK (DICT_VERSION_INCREMENT - 1)

#ifdef Py_GIL_DISABLED
#define DICT_NEXT_VERSION(INTERP) \
(_Py_atomic_add_uint64(&(INTERP)->dict_state.global_version, DICT_VERSION_INCREMENT) + DICT_VERSION_INCREMENT)
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I think this is fine for now, especially in the interest of getting to the point where we can run the test suite with the GIL disabled, but we will want to avoid contention on the global version counter.

The strategy in nogil and nogil-3.12 was to reserve something like the next 256 versions (atomically) and then serve the next version requests from thread-local state.

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For reference: https://github.com/colesbury/nogil-3.12/blob/cedde4f5ec3759ad723c89d44738776f362df564/Include/internal/pycore_dict.h#L169-L177

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Oh, nice!


#else
#define DICT_NEXT_VERSION(INTERP) \
((INTERP)->dict_state.global_version += DICT_VERSION_INCREMENT)
#endif

void
_PyDict_SendEvent(int watcher_bits,
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