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Free threading scaling bottleneck in sys.intern() #146041
Description
Bug report
Calling sys.intern() on a string that's not interned acquires the interpreter-wide interned_mutex. This can lead to scaling bottlenecks either due to explicit sys.intern() calls or indirectly because PyObject_SetAttr calls _PyUnicode_InternMortal.
We should avoid the lock acquisition if there is an interned copy already present in the interned_dict.
For example:
_ATTR_PREFIX = "bench"
@register_benchmark
def setattr_non_interned():
prefix = _ATTR_PREFIX
obj = MyObject()
for _ in range(1000 * WORK_SCALE):
setattr(obj, f"{prefix}_a", None)
setattr(obj, f"{prefix}_b", None)
setattr(obj, f"{prefix}_c", None)This came up when looking at Django scaling bottlenecks.
Activity
FocusMode-coder commentedon Mar 16, 2026
pythongh-146041: Avoid lock in sys.intern() for already interned strings
pythongh-146041: Avoid lock in sys.intern() for already interned strings
pythongh-146041: Avoid lock in sys.intern() for already interned strings
pythongh-146041: Avoid lock in sys.intern() for already interned strings
Merge branch 'main' into pythongh-146041-intern-lock-free
gh-146041: Avoid lock in sys.intern() for already interned strings (g…
[3.14] pythongh-146041: Avoid lock in sys.intern() for already intern…
[3.14] gh-146041: Avoid lock in sys.intern() for already interned str…
pythongh-146041: Avoid lock in sys.intern() for already interned stri…
pythongh-146041: Avoid lock in sys.intern() for already interned stri…