Ludovic Marie
59 lines
3.8 KiB
Markdown
59 lines
3.8 KiB
Markdown
# Avoid allocating iterators for empty culling whitelists
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A local game JFR found `HashMap.KeySet` iterator allocation in Entity Culling's
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dynamic entity/block-entity whitelist checks on `CullThread`. The pinned 1.11.2
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methods create a set iterator before discovering that there are no handlers.
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The optional hook returns the JDK's shared empty iterator while the live set is
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empty. It checks that set every call; it does not cache a whitelist, remember an
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empty state, skip a registered handler, or alter culling decisions. Nonempty
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sets use their original iterator, callback order, type guard and short circuit.
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No per-call callback object is introduced by the hook.
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Use the `culling-empty` profile for an isolated comparison with `m2-balanced`.
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Both keep the same graphics, LOD radius, worker budget and other controller
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settings. The hook is opt-in, restricted to Entity Culling 1.11.2, and can be
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disabled with `enabled=false` in `config/horizon-culling-empty.properties` and a
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restart. Frame reports record `empty_culling_whitelist`; the CLI and offline
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viewer disclose a difference as an experiment variable.
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`python tools/test_culling_empty.py` runs the actual publisher methods inside
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Fabric. It checks empty iterator dispatch, registration after initialization,
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duplicate registration, real block-entity callback order/short circuit, null and
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wrong-type inputs, and returning to an empty state. The menu-only fixture does
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not exercise callbacks using a valid world entity; nonempty entity iteration
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uses the original implementation. Private instrumentation and fixture JARs
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never enter release packs. Full game logs remain private.
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A local warmed loop of four million empty checks allocated 128,001,248 bytes
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upstream versus 1,248 with the hook. CPU was 41 ms versus 33 ms in that single
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observation. These counts isolate this allocation path; JIT escape analysis can
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produce different results in other calling contexts. They are not game FPS,
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whole-game RAM, statistical speed estimates or Mac GPU results. Repeated matching workloads and real hardware tests remain needed. A fixed-order
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Linux software-rendered pair observed about 97,445 versus 35,128 allocated bytes
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per second on `CullThread`, over separate 64-second counter spans. The captured
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graphics matched and both recordings excluded zero frames, but this one pair is
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not a repeatable FPS or retained-RAM result. The candidate also encountered an
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intermittent shutdown wait after its world had saved; the control exited normally.
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See the [terrain read shutdown check](terrain-read-wait.md).
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For local world smoke checks, the baseline and candidate use separate copies of
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the same peaceful demo-world snapshot. An earlier capture was interrupted by a
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zombie killing the player and is excluded from performance comparisons. Release
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packs do not change world difficulty. Frame reports now capture actual world
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difficulty at their start/end boundaries so comparison tools can flag a mismatch.
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The [sanitized Linux CI result](../benchmarks/culling-empty-2026-10-04/linux-applied-hooks.json)
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includes its source/workflow provenance and independently checks live registration
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and the applied shortcut. CPU timings can include JIT folding of this empty loop;
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they are not per-check costs or estimates of game speed.
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The final candidate JAR (`c506982631880604513de8ef85e3b4461fbb898702e60b4a6f74ca3b3d4a687f`)
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then recorded 579 frame intervals and 2,408 integrated-server tick durations over
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120 seconds, with zero excluded frames and matching CSV counts/means. Its actual
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frame report retained custom graphics, render/simulation distances 12/12, DH radius
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128 at MEDIUM/MEDIUM quality, two workers at runtime ratio 0.5, compact headers,
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and both the culling shortcut and scoped terrain-read fix enabled. No captured
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visual setting changed. This verifies integration; it is not a repeated hardware
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performance comparison.
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