Add FlatHashtable open-addressed find-or-create collection#11980
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Add FlatHashtable open-addressed find-or-create collection#11980dougqh wants to merge 2 commits into
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…hism helpers A reusable open-addressed table over self-contained entries (one reference per slot), designed so callers specialize it via a concrete-typed static-final Helper that the JIT devirtualizes and inlines (C++-template-style static polymorphism). Cardinality cap / overflow / size are caller policy; this class is pure mechanism (capacityFor, create, get, getOrCreate). Includes a String-key StringHelper that seals a spread hash. Intended as the shared backing for several open-addressed caches/tables (per-operation sizing hints, UTF8BytesString caches, etc.). Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
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Force hash collisions via fixed-hash helpers to exercise the linear-probe paths the original tests missed: probe-past-occupied + match-after-probe (in both get and getOrCreate), wraparound to the front, and get()'s full-table wrap-to-null branch. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
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From Claude:
A reusable open-addressed table over self-contained entries — one reference per slot, so entry publication is a single reference store and readers see null-or-complete (no torn reads, no
volatile/atomics needed when the payload makes a stale/lost read benign).Callers specialize it via a concrete-typed
static finalHelper(orStringHelper) that the JIT devirtualizes and inlines — C++-template-style static polymorphism: one algorithm, one monomorphic instantiation per call site.Helperis an abstract class on purpose (forces a named type;invokevirtualfallback if inlining ever misses);StringHelperseals a spreadhashso String-key callers write onlymatches/create.Pure mechanism —
capacityFor,create(typed backing array viaArray.newInstance),get,getOrCreate. Cardinality cap / overflow / a live-size counter are caller policy.Intended as the shared backing for several open-addressed caches/tables (per-operation sizing hints,
UTF8BytesStringcaches, …). This PR is just the standalone collection + unit tests; callers land separately.Draft caveat: authored without a local module build (to stay off an in-progress release), so
spotlessCheck/spotbugsMain/ compile want CI (or aspotlessApplypass) to confirm.🤖 Generated with Claude Code