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perf: avoid scanning the type cache on type mutation - #8628
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Assisted-by: Codex:gpt-5.6-sol
Assisted-by: Codex:gpt-5.6-sol
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Summary
Type mutation previously invalidated method-cache entries by scanning all 4,096 slots for the type's old version tag. This made every cached type mutation pay for a full-cache scan.
This change invalidates the type by setting its version tag to zero and leaves the old cache entry in place. Type version tags are monotonic and never reused; once the counter is exhausted, new tag assignment remains disabled. Cache readers accept an entry only when its version and interned name match the type's current version under the existing sequence-lock protocol, so an entry for an invalidated version is unreachable.
Cached values are already marked as published and use QSBR-delayed allocation reclamation, which lets an in-flight reader that observed the old version finish its conditional incref safely. The existing whole-cache clear still nulls every borrowed pointer before cyclic GC breaks type reference cycles.
This also adds a microbenchmark for repeated cached lookup followed by type mutation, plus focused tests for version reachability and concurrent cache readers.
Performance
benches/microbenchmarks/type_cache_invalidation.pycompares the benchmark-only commit with the invalidation change:AI assistance
Codex (
gpt-5.6-sol) assisted extensively with the implementation, tests, benchmark setup and analysis, automated validation, code review, and drafting this PR description.