feat: use os.availableParallelism if available

CHANGELOG.md

@@ -2,8 +2,9 @@
 
 ### Features
 
-- `[@jest/globals, jest-mock]` Add `jest.replaceProperty()` that replaces property value ([#13496](https://github.com/facebook/jest/pull/13496))
 - `[expect, @jest/expect-utils]` Support custom equality testers ([#13654](https://github.com/facebook/jest/pull/13654))
+- `[jest-config, jest-worker]` Use `os.availableParallelism` if available to calculate number of workers to spawn ([#13738](https://github.com/facebook/jest/pull/13738))
+- `[@jest/globals, jest-mock]` Add `jest.replaceProperty()` that replaces property value ([#13496](https://github.com/facebook/jest/pull/13496))
 - `[jest-haste-map]` ignore Sapling vcs directories (`.sl/`) ([#13674](https://github.com/facebook/jest/pull/13674))
 - `[jest-resolve]` Support subpath imports ([#13705](https://github.com/facebook/jest/pull/13705), [#13723](https://github.com/facebook/jest/pull/13723))
 - `[jest-runtime]` Add `jest.isolateModulesAsync` for scoped module initialization of asynchronous functions ([#13680](https://github.com/facebook/jest/pull/13680))

packages/jest-config/src/__mocks__/os.js

@@ -17,4 +17,8 @@ function __setCpus(newCpus) {
 os.__setCpus = __setCpus;
 os.cpus = jest.fn(() => cpus);
 
+if (typeof os.availableParallelism === 'function') {
+  os.availableParallelism = jest.fn(() => cpus?.length ?? 0);
+}
+
 module.exports = os;

packages/jest-config/src/getMaxWorkers.ts

@@ -5,9 +5,19 @@
  * LICENSE file in the root directory of this source tree.
  */
 
-import {cpus} from 'os';
+import {
+  // @ts-expect-error - added in Node 19.4.0
+  availableParallelism,
+  cpus,
+} from 'os';
 import type {Config} from '@jest/types';
 
+function getNumCpus(): number {
+  return typeof availableParallelism === 'function'
+    ? availableParallelism()
+    : cpus()?.length ?? 1;
+}
+
 export default function getMaxWorkers(
   argv: Partial<
     Pick<Config.Argv, 'maxWorkers' | 'runInBand' | 'watch' | 'watchAll'>
@@ -22,8 +32,7 @@ export default function getMaxWorkers(
     return parseWorkers(defaultOptions.maxWorkers);
   } else {
     // In watch mode, Jest should be unobtrusive and not use all available CPUs.
-    const cpusInfo = cpus();
-    const numCpus = cpusInfo?.length ?? 1;
+    const numCpus = getNumCpus();
     const isWatchModeEnabled = argv.watch || argv.watchAll;
     return Math.max(
       isWatchModeEnabled ? Math.floor(numCpus / 2) : numCpus - 1,
@@ -41,7 +50,7 @@ const parseWorkers = (maxWorkers: string | number): number => {
     parsed > 0 &&
     parsed <= 100
   ) {
-    const numCpus = cpus().length;
+    const numCpus = getNumCpus();
     const workers = Math.floor((parsed / 100) * numCpus);
     return Math.max(workers, 1);
   }

packages/jest-repl/src/cli/runtime-cli.ts

@@ -5,7 +5,11 @@
  * LICENSE file in the root directory of this source tree.
  */
 
-import {cpus} from 'os';
+import {
+  // @ts-expect-error - added in Node 19.4.0
+  availableParallelism,
+  cpus,
+} from 'os';
 import * as path from 'path';
 import * as util from 'util';
 import chalk = require('chalk');
@@ -70,8 +74,13 @@ export async function run(
   };
 
   try {
+    const numCpus: number =
+      typeof availableParallelism === 'function'
+        ? availableParallelism()
+        : cpus().length;
+
     const hasteMap = await Runtime.createContext(projectConfig, {
-      maxWorkers: Math.max(cpus().length - 1, 1),
+      maxWorkers: Math.max(numCpus - 1, 1),
       watchman: globalConfig.watchman,
     });
 

packages/jest-worker/src/index.ts

@@ -5,7 +5,11 @@
  * LICENSE file in the root directory of this source tree.
  */
 
-import {cpus} from 'os';
+import {
+  // @ts-expect-error - added in Node 19.4.0
+  availableParallelism,
+  cpus,
+} from 'os';
 import {isAbsolute} from 'path';
 import Farm from './Farm';
 import WorkerPool from './WorkerPool';
@@ -54,6 +58,12 @@ function getExposedMethods(
   return exposedMethods;
 }
 
+function getNumberOfCpus(): number {
+  return typeof availableParallelism === 'function'
+    ? availableParallelism()
+    : cpus().length;
+}
+
 /**
  * The Jest farm (publicly called "Worker") is a class that allows you to queue
  * methods across multiple child processes, in order to parallelize work. This
@@ -98,7 +108,8 @@ export class Worker {
       forkOptions: this._options.forkOptions ?? {},
       idleMemoryLimit: this._options.idleMemoryLimit,
       maxRetries: this._options.maxRetries ?? 3,
-      numWorkers: this._options.numWorkers ?? Math.max(cpus().length - 1, 1),
+      numWorkers:
+        this._options.numWorkers ?? Math.max(getNumberOfCpus() - 1, 1),
       resourceLimits: this._options.resourceLimits ?? {},
       setupArgs: this._options.setupArgs ?? [],
     };

scripts/buildTs.mjs

@@ -110,7 +110,12 @@ try {
 console.log(chalk.inverse(' Validating TypeScript definition files '));
 
 // we want to limit the number of processes we spawn
-const cpus = Math.max(1, os.cpus().length - 1);
+const cpus = Math.max(
+  1,
+  (typeof os.availableParallelism === 'function'
+    ? os.availableParallelism()
+    : os.cpus().length) - 1,
+);
 
 const typesReferenceDirective = '/// <reference types';
 const typesNodeReferenceDirective = `${typesReferenceDirective}="node" />`;

scripts/lintTs.mjs

@@ -14,7 +14,13 @@ import pLimit from 'p-limit';
 import {getPackagesWithTsConfig} from './buildUtils.mjs';
 
 // we want to limit the number of processes we spawn
-const cpus = Math.max(1, os.cpus().length - 1);
+const cpus = Math.max(
+  1,
+  (typeof os.availableParallelism === 'function'
+    ? os.availableParallelism()
+    : os.cpus().length) - 1,
+);
+
 const mutex = pLimit(cpus);
 
 const fix = process.argv.slice(2).some(arg => arg === '--fix');