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Merged
chenjiahan merged 1 commit into from
Aug 3, 2026
Merged

perf(fmt): cap default worker count at eight #149

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7 changes: 6 additions & 1 deletion packages/rstack/src/fmt/workerPool.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -14,8 +14,13 @@ interface FmtWorkerPool {
terminate: () => Promise<void>;
}

/**
* Caps the default worker count at 8 because formatter throughput can
* plateau before all CPU cores are occupied, while additional workers increase
* scheduling and memory pressure.
*/
const getFmtWorkerCount = (fileCount: number, maxWorkers?: number): number =>
Math.min(fileCount, maxWorkers ?? Math.max(1, availableParallelism() - 1));
Math.min(fileCount, maxWorkers ?? Math.min(8, Math.max(1, availableParallelism() - 1)));

const getFmtWorkerUrl = (): URL => {
// Source tests run after build and exercise the same worker artifact as the CLI.
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8 changes: 1 addition & 7 deletions packages/rstack/tests/fmt/workerPool.test.ts
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Original file line number Diff line number Diff line change
@@ -1,17 +1,11 @@
import { availableParallelism } from 'node:os';
import { expect, test } from 'rstack/test';
import { getFmtWorkerCount } from '../../src/fmt/workerPool.ts';

test('uses one fewer worker than the available parallelism by default', () => {
const defaultWorkerCount = Math.max(1, availableParallelism() - 1);

expect(getFmtWorkerCount(defaultWorkerCount + 1)).toBe(defaultWorkerCount);
});

test.each([
[4, 1, 1],
[4, 2, 2],
[2, 4, 2],
[12, 10, 10],
])('uses %s files and %s configured workers as %s workers', (files, workers, expected) => {
expect(getFmtWorkerCount(files, workers)).toBe(expected);
});