the great bench

bench/churn.ts

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+// bench/churn.ts
+import { Bench } from "tinybench";
+import { type Box, box } from "./../engine/lib/box.ts";
+import {
+	createDictionary,
+	deleteEntry,
+	getEntry,
+	setEntry,
+} from "./../engine/lib/Dictionary.ts";
+import MapArray from "./../engine/lib/MapArray.ts";
+
+const bench = new Bench({ name: "churn", time: 1000 });
+
+const SIZE = 999;
+const baseData: Array<[string, Box<number>]> = [];
+{
+	let i = SIZE;
+	while (i-- > 0) baseData.push([String(i), box(i)]);
+}
+
+// Churn keys: a rotating window of "new" entities not in the base set,
+// so every set/delete pair actually does real insert+remove work
+// rather than repeatedly hitting the same already-resident key.
+const CHURN_N = 100;
+const churnKeys = Array.from({ length: CHURN_N }, (_, i) => `churn-${i}`);
+
+let sink = 0; // anti-DCE: something observable reads this later
+
+function freshMapArray() {
+	return new MapArray(structuredClone(baseData));
+}
+function freshDictionary() {
+	return createDictionary(structuredClone(baseData));
+}
+function freshMap() {
+	return new Map(structuredClone(baseData));
+}
+
+// Each task rebuilds nothing per-iteration except doing insert+remove
+// on a fixed churn window against a persistent SIZE-element base structure —
+// this mirrors "N entities steady-state, M entering/leaving per frame".
+const ma = freshMapArray();
+const dict = freshDictionary();
+const map = freshMap();
+
+bench
+	.add("MapArray churn (set+delete)", () => {
+		for (const key of churnKeys) {
+			ma.set(key, box(1));
+		}
+		for (const key of churnKeys) {
+			ma.delete(key);
+		}
+		sink += ma.entries().length;
+	})
+	.add("Dictionary churn (set+delete)", () => {
+		for (const key of churnKeys) {
+			setEntry(dict, [key, box(1)]);
+		}
+		for (const key of churnKeys) {
+			deleteEntry(dict, key);
+		}
+		sink += dict.entries.length;
+	})
+	.add("Map churn (set+delete)", () => {
+		for (const key of churnKeys) {
+			map.set(key, box(1));
+		}
+		for (const key of churnKeys) {
+			map.delete(key);
+		}
+		sink += map.size;
+	});
+
+await bench.run();
+console.table(bench.table());
+console.log("sink (ignore):", sink);