8000 gh-134761: Use deferred reference counting for `threading` concurrency primitives by ZeroIntensity · Pull Request #134762 · python/cpython · GitHub
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gh-134761: Use deferred reference counting for threading concurrency primitives #134762

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gh-134761: Use deferred reference counting for threading concurrency primitives #134762

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e02137e
Use deferred reference counting for threading primitives.
ZeroIntensity May 26, 2025
6093acb
Document and test sys._defer_refcount()
ZeroIntensity May 26, 2025
478d482
Add blurb.
ZeroIntensity May 26, 2025
f0fc73c
Remove sys._defer_refcount() documentation.
ZeroIntensity May 27, 2025
d407ad9
Remove stray newline change.
ZeroIntensity May 27, 2025
c750d92
Move call to _PyObject_SetDeferredRefcount()
ZeroIntensity May 27, 2025
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Document and test sys._defer_refcount()
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@ZeroIntensity
ZeroIntensity committed May 26, 2025
commit 6093acb1bd747e4e6bd6e067828bc1a2d44c05ac
19 changes: 19 additions & 0 deletions Doc/library/sys.rst
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Expand Up @@ -290,6 +290,25 @@ always available. Unless explicitly noted otherwise, all variables are read-only
This function is specific to CPython. The exact output format is not
defined here, and may change.

.. function:: _defer_refcount(op)
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Did not take a look overall but not sure it is worth to to expose it through the documentation since this is not a public api.

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Yeah, I'm a little bit on the fence about it. We do this already for some other functions in sys: _is_gil_enabled, _is_interned, _is_immortal, and a few others. Basically, it's a way to expose implementation details that are useful at a Python level.

Overall, I think this is worth documenting. There's no other way to improve scaling from Python right now, and it's similar to using an unstable C API (in the sense that it could be removed in any version).

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What about documenting this in https://github.com/python/cpython/tree/main/InternalDocs somewhere? I fully agree with removing this from the normal documentation (for the reasons mentioned), but as a user/developer/tester I find the python api to _defer_refcount (and others like _is_immortal) useful and some documentation is always nice.


Enable deferred reference counting on *op*, mitigating reference count
contention on :term:`free threaded <free threading>` builds of Python.

Return :const:`True` if deferred reference counting was enabled on *op*,
and :const:`False` otherwise.

.. versionadded:: next

.. impl-detail::

This function should be used for specialized purposes only.
It is not guaranteed to exist in all implementations of Python.

.. seealso::

:c:func:`PyUnstable_Object_EnableDeferredRefcount`


.. data:: dllhandle

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19 changes: 19 additions & 0 deletions Lib/test/test_sys.py
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Expand Up @@ -1343,6 +1343,25 @@ def test_pystats(self):
def test_disable_gil_abi(self):
self.assertEqual('t' in sys.abiflags, support.Py_GIL_DISABLED)

@test.support.cpython_only
@unittest.skipUnless(hasattr(sys, '_defer_refcount'), "requires _defer_refcount()")
def test_defer_refcount(self):
_testinternalcapi = import_helper.import_module('_testinternalcapi')

class Test:
pass

ref = Test()
if support.Py_GIL_DISABLED:
self.assertTrue(sys._defer_refcount(ref))
self.assertTrue(_testinternalcapi.has_deferred_refcount(ref))
self.assertFalse(sys._defer_refcount(ref))
self.assertFalse(sys._defer_refcount(42))
else:
self.assertFalse(sys._defer_refcount(ref))
self.assertFalse(_testinternalcapi.has_deferred_refcount(ref))
self.assertFalse(sys._defer_refcount(42))


@test.support.cpython_only
class UnraisableHookTest(unittest.TestCase):
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