[mypyc] Make type objects immortal if using free threading #19538
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If they are not immortal, concurrent construction objects by multiple threads can cause serious contention due to reference count updates. This is similar how user-defined normal Python classes in free-threaded builds are immmortal. This speeds up a micro-benchmark that constructs instances of a native class in multiple threads by a big factor (5x+).
p-sawicki
approved these changes
Jul 30, 2025
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If they are not immortal, concurrent construction of objects by multiple
threads can cause serious contention due to reference count updates.
Making them immortal is similar to how both user-defined normal Python
classes and built-in types in free-threaded builds are immortal.
Fix the issue for both native and non-native classes. Dataclasses still have
contention, and they may be harder to fix (this may require a fix in CPython).
This speeds up a few micro-benchmarks that construct instances of classes
in multiple threads by a big factor (5x+).