beartype / plum / 29708487956

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Make concurrent dispatch resolution thread-safe (#281)

Protect `Function`'s first-time dispatch resolution and cache clearing with a per-instance reentrant lock, eliminating races when multiple threads resolve the same function concurrently. A double-checked locking strategy keeps the already-resolved hot path lock-free while preventing concurrent mutation of deferred annotations during initial resolution.

Add a deterministic regression test exercising concurrent first resolution, refactor the test scaffolding to use a factory fixture so each iteration receives a fresh dispatcher, and update the accompanying documentation and comments. This change addresses the dispatch-resolution race only; the independent upstream beartype lazy-compilation race is fixed upstream.

Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>
Co-authored-by: Wessel <wessel.p.bruinsma@gmail.com>

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