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fix(benchmark.js): collect garbage before synchronous measurements #112

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fix(benchmark.js): collect garbage before synchronous measurements #112

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7 changes: 7 additions & 0 deletions docs/introspection.md
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Expand Up @@ -13,3 +13,10 @@
```bash
CI=1 CODSPEED_DEBUG=true pnpm --filter with-typescript-esm bench-tinybench
```

## Garbage collection

Memory and simulation modes receive `--expose-gc` through introspection.
The Benchmark.js plugin collects warmup garbage before starting instrumentation
for both synchronous and asynchronous benchmarks. This keeps the forced
collection outside the measured window.
1 change: 1 addition & 0 deletions packages/benchmark.js-plugin/src/index.ts
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Expand Up @@ -207,6 +207,7 @@ async function runBenchmarks({
} else {
optimizeFunctionSync(benchPayload);
await mongoMeasurement.start(uri);
global.gc?.();

@greptile-apps greptile-apps Bot Oct 29, 2026

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P2 GC ordering has no test

The new collection has no regression test. Existing tests check that startBenchmark runs, but not whether global.gc runs before it. Removing this fix or moving collection into the measured window would still pass those tests.

Add a temporary global.gc mock and check that collection runs after warmup and before startBenchmark. Also cover missing GC and fallback execution, and restore the original global afterward.

Prompt To Fix With AI 
This is a comment left during a code review.
Path: packages/benchmark.js-plugin/src/index.ts
Line: 210

Comment:
**GC ordering has no test**

The new collection has no regression test. Existing tests check that `startBenchmark` runs, but not whether `global.gc` runs before it. Removing this fix or moving collection into the measured window would still pass those tests.

Add a temporary `global.gc` mock and check that collection runs after warmup and before `startBenchmark`. Also cover missing GC and fallback execution, and restore the original global afterward.

---

For each issue above, determine whether it is valid and should be fixed. If so, fix it directly.

Note: If this suggestion doesn't match your team's coding style, reply to this and let me know. I'll remember it for next time!

Fix in Claude Code Fix in Codex

wrapWithRootFrameSync(() => {
InstrumentHooks.startBenchmark();
benchPayload();
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