Simplify cpuCount utility and add limiting functionality

packages/core/workers/src/WorkerFarm.js

@@ -22,7 +22,7 @@ import {
 } from '@parcel/core';
 import ThrowableDiagnostic, {anyToDiagnostic, md} from '@parcel/diagnostic';
 import Worker, {type WorkerCall} from './Worker';
-import cpuCount from './cpuCount';
+import {getCoreCount} from './cpuCount';
 import Handle from './Handle';
 import {child} from './childState';
 import {detectBackend} from './backend';
@@ -557,7 +557,7 @@ export default class WorkerFarm extends EventEmitter {
   static getNumWorkers(): number {
     return process.env.PARCEL_WORKERS
       ? parseInt(process.env.PARCEL_WORKERS, 10)
-      : cpuCount();
+      : getCoreCount();
   }
 
   static isWorker(): boolean {

packages/core/workers/src/cpuCount.js

@@ -1,66 +1,7 @@
 // @flow
 import os from 'os';
-import {execSync} from 'child_process';
 
-const exec = (command: string): string => {
-  try {
-    let stdout = execSync(command, {
-      encoding: 'utf8',
-      // This prevents the command from outputting to the console
-      stdio: [null, null, null],
-    });
-    return stdout.trim();
-  } catch (e) {
-    return '';
-  }
-};
-
-export function detectRealCores(): number {
-  let platform = os.platform();
-  let amount = 0;
-
-  if (platform === 'linux') {
-    amount = parseInt(
-      exec('lscpu -p | egrep -v "^#" | sort -u -t, -k 2,4 | wc -l'),
-      10,
-    );
-  } else if (platform === 'darwin') {
-    amount = parseInt(exec('sysctl -n hw.physicalcpu_max'), 10);
-  } else if (platform === 'win32') {
-    const str = exec('wmic cpu get NumberOfCores').match(/\d+/g);
-    if (str !== null) {
-      amount = parseInt(str.filter(n => n !== '')[0], 10);
-    }
-  }
-
-  if (!amount || amount <= 0) {
-    throw new Error('Could not detect cpu count!');
-  }
-
-  return amount;
-}
-
-let cores;
-export default function getCores(bypassCache?: boolean = false): number {
-  // Do not re-run commands if we already have the count...
-  if (cores && !bypassCache) {
-    return cores;
-  }
-
-  try {
-    cores = detectRealCores();
-  } catch (e) {
-    // Guess the amount of real cores
-    cores = os
-      .cpus()
-      .filter((cpu, index) => !cpu.model.includes('Intel') || index % 2 === 1)
-      .length;
-  }
-
-  // Another fallback
-  if (!cores) {
-    cores = 1;
-  }
-
-  return cores;
+export function getCoreCount(limit: number = 8): number {
+  let coreCount = Math.ceil(os.cpus().length / 2);
+  return Math.max(Math.min(coreCount, limit), 1);
 }

packages/core/workers/test/cpuCount.test.js

@@ -1,19 +1,23 @@
 import assert from 'assert';
 import os from 'os';
 
-import getCores, {detectRealCores} from '../src/cpuCount';
+import {getCoreCount} from '../src/cpuCount';
 
-describe('cpuCount', function() {
-  it('Should be able to detect real cpu count', () => {
-    // Windows not supported as getting the cpu count takes a couple seconds...
-    if (os.platform() === 'win32') return;
+let cpus = os.cpus().length;
 
-    let cores = detectRealCores();
+describe('cpuCount', function() {
+  it('getCoreCount should return more than 0', () => {
+    let cores = getCoreCount();
     assert(cores > 0);
   });
 
-  it('getCores should return more than 0', () => {
-    let cores = getCores(true);
-    assert(cores > 0);
-  });
+  if (cpus > 2) {
+    it('Should be able to limit coreCount', () => {
+      let allCores = getCoreCount();
+      let limitedCores = getCoreCount(1);
+
+      assert(allCores > limitedCores);
+      assert.equal(limitedCores, 1);
+    });
+  }
 });