[3.14] gh-145685: Stop the world when updating MRO of existing types (gh-145707)#145715

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[3.14] gh-145685: Stop the world when updating MRO of existing types (gh-145707)#145715
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colesbury commentedMar 9, 2026•
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We already have a stop-the-world pause elsewhere in this code path (type_set_bases) and this makes will make it easier to avoid contention on the TYPE_LOCK when looking up names in the MRO hierarchy.

Also use deferred reference counting for non-immortal MROs.
(cherry picked from commit0b65c88)

Issue:Unexpected scaling bottleneck in_PyType_Lookup /_PyType_LookupStackRefAndVersion #145685

[3.14]pythongh-145685: Stop the world when updating MRO of existing …

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…types (pythongh-145707)We already have a stop-the-world pause elsewhere in this code path(type_set_bases) and this makes will make it easier to avoid contentionon the TYPE_LOCK when looking up names in the MRO hierarchy.Also use deferred reference counting for non-immortal MROs.(cherry picked from commit0b65c88)Co-authored-by: Sam Gross <colesbury@gmail.com>