feat: optimize getMaxWorkers using os.availableParallelism

docs/Configuration.md

@@ -143,7 +143,7 @@ If `true`, Metro will use a stable mapping from files to transformer workers, so
 
 Type: `number`
 
-The number of workers to use for parallel processing in Metro. Defaults to approximately half of the number of cores available on the machine, as reported by [`os.cpus()`](https://nodejs.org/api/os.html#oscpus).
+The number of workers to use for parallel processing in Metro. Defaults to approximately half of the number of cores available on the machine, as reported by [`os.availableParallelism()`](https://nodejs.org/api/os.html#osavailableparallelism).
 
 :::note
 1. Values exceeding the number of available cores have no effect.

packages/metro/src/lib/__tests__/getMaxWorkers-test.js

@@ -20,17 +20,17 @@ test('calculates the number of max workers', () => {
   /* $FlowFixMe(>=0.99.0 site=react_native_fb) This comment suppresses an error
    * found when Flow v0.99 was deployed. To see the error, delete this comment
    * and run Flow. */
-  os.cpus.mockReturnValue({length: 1});
+  os.availableParallelism.mockReturnValue(1);
   expect(getMaxWorkers()).toBe(1);
   /* $FlowFixMe(>=0.99.0 site=react_native_fb) This comment suppresses an error
    * found when Flow v0.99 was deployed. To see the error, delete this comment
    * and run Flow. */
-  os.cpus.mockReturnValue({length: 8});
+  os.availableParallelism.mockReturnValue(8);
   expect(getMaxWorkers()).toBe(6);
   /* $FlowFixMe(>=0.99.0 site=react_native_fb) This comment suppresses an error
    * found when Flow v0.99 was deployed. To see the error, delete this comment
    * and run Flow. */
-  os.cpus.mockReturnValue({length: 24});
+  os.availableParallelism.mockReturnValue(24);
   expect(getMaxWorkers()).toBe(14);
   expect(getMaxWorkers(5)).toBe(5);
 });

packages/metro/src/lib/getMaxWorkers.js

@@ -14,7 +14,8 @@
 const os = require('os');
 
 module.exports = (workers: ?number): number => {
-  const cores = os.cpus().length;
+  // $FlowFixMe[prop-missing] Missing Flow lib def for availableParallelism
+  const cores = os.availableParallelism();
   return typeof workers === 'number' && Number.isInteger(workers)
     ? Math.min(cores, workers > 0 ? workers : 1)
     : Math.max(1, Math.ceil(cores * (0.5 + 0.5 * Math.exp(-cores * 0.07)) - 1));