packager: Bundler: refactor the maxWorkerCount

Summary: The function giving the worker count was duplicated, let's just pass it down from a central place, the Bundler. Also, I simplified the function to use a simple formula rather than arbitrary ranges (it's still arbitrary, just a tad bit less :D ).

Reviewed By: davidaurelio

Differential Revision: D4689366

fbshipit-source-id: fe5b349396f1a07858f4f80ccaa63c375122fac8

packages/metro-bundler/src/Bundler/__tests__/Bundler-test.js

@@ -15,6 +15,7 @@ jest
   .setMock('uglify-js')
   .mock('image-size')
   .mock('fs')
+  .mock('os')
   .mock('assert')
   .mock('progress')
   .mock('../../node-haste')
@@ -31,6 +32,7 @@ var Resolver = require('../../Resolver');
 var defaults = require('../../../defaults');
 var sizeOf = require('image-size');
 var fs = require('fs');
+const os = require('os');
 
 var commonOptions = {
   allowBundleUpdates: false,
@@ -76,6 +78,8 @@ describe('Bundler', function() {
   var projectRoots;
 
   beforeEach(function() {
+    os.cpus.mockReturnValue({length: 1});
+
     getDependencies = jest.fn();
     getModuleSystemDependencies = jest.fn();
     projectRoots = ['/root'];
@@ -348,5 +352,16 @@ describe('Bundler', function() {
           '/root/img/new_image2@3x.png',
         ]));
     });
+
+    it('return correct number of workers', () => {
+      os.cpus.mockReturnValue({length: 1});
+      expect(Bundler.getMaxWorkerCount()).toBe(1);
+      os.cpus.mockReturnValue({length: 8});
+      expect(Bundler.getMaxWorkerCount()).toBe(6);
+      os.cpus.mockReturnValue({length: 24});
+      expect(Bundler.getMaxWorkerCount()).toBe(14);
+      process.env.REACT_NATIVE_MAX_WORKERS = 5;
+      expect(Bundler.getMaxWorkerCount()).toBe(5);
+    });
   });
 });

packages/metro-bundler/src/Bundler/index.js

@@ -25,6 +25,8 @@ const imageSize = require('image-size');
 const path = require('path');
 const denodeify = require('denodeify');
 const defaults = require('../../defaults');
+const os = require('os');
+const invariant = require('fbjs/lib/invariant');
 
 const {
   sep: pathSeparator,
@@ -163,8 +165,10 @@ class Bundler {
       cacheKey: transformCacheKey,
     });
 
+    const maxWorkerCount = Bundler.getMaxWorkerCount();
+
     /* $FlowFixMe: in practice it's always here. */
-    this._transformer = new Transformer(opts.transformModulePath);
+    this._transformer = new Transformer(opts.transformModulePath, maxWorkerCount);
 
     const getTransformCacheKey = (src, filename, options) => {
       return transformCacheKey + getCacheKey(src, filename, options);
@@ -178,6 +182,7 @@ class Bundler {
       getTransformCacheKey,
       globalTransformCache: opts.globalTransformCache,
       hasteImpl: opts.hasteImpl,
+      maxWorkerCount,
       minifyCode: this._transformer.minify,
       moduleFormat: opts.moduleFormat,
       platforms: new Set(opts.platforms),
@@ -780,6 +785,26 @@ class Bundler {
   getResolver(): Promise<Resolver> {
     return this._resolverPromise;
   }
+
+  /**
+   * Unless overriden, we use a diminishing amount of workers per core, because
+   * using more and more of them does not scale much. Ex. 6 workers for 8
+   * cores, or 14 workers for 24 cores.
+   */
+  static getMaxWorkerCount() {
+    const cores = os.cpus().length;
+    const envStr = process.env.REACT_NATIVE_MAX_WORKERS;
+    if (envStr == null) {
+      return Math.max(1, Math.ceil(cores * (0.5 + 0.5 * Math.exp(-cores * 0.07)) - 1));
+    }
+    const envCount = parseInt(process.env.REACT_NATIVE_MAX_WORKERS, 10);
+    invariant(
+      Number.isInteger(envCount),
+      'environment variable `REACT_NATIVE_MAX_WORKERS` must be a valid integer',
+    );
+    return Math.min(cores, envCount);
+  }
+
 }
 
 function getPathRelativeToRoot(roots, absPath) {

packages/metro-bundler/src/JSTransformer/index.js

@@ -16,7 +16,6 @@ const Logger = require('../Logger');
 const debug = require('debug')('RNP:JStransformer');
 const denodeify = require('denodeify');
 const invariant = require('fbjs/lib/invariant');
-const os = require('os');
 const path = require('path');
 const util = require('util');
 const workerFarm = require('worker-farm');
@@ -35,24 +34,7 @@ const TRANSFORM_TIMEOUT_INTERVAL = 301000;
 // How may times can we tolerate failures from the worker.
 const MAX_RETRIES = 2;
 
-const maxConcurrentWorkers = ((cores, override) => {
-  if (override) {
-    return Math.min(cores, override);
-  }
-
-  if (cores < 3) {
-    return cores;
-  }
-  if (cores < 8) {
-    return Math.floor(cores * 0.75);
-  }
-  if (cores < 24) {
-    return Math.floor(3 / 8 * cores + 3); // between cores *.75 and cores / 2
-  }
-  return cores / 2;
-})(os.cpus().length, parseInt(process.env.REACT_NATIVE_MAX_WORKERS, 10));
-
-function makeFarm(worker, methods, timeout) {
+function makeFarm(worker, methods, timeout, maxConcurrentWorkers) {
   return workerFarm(
     {
       autoStart: true,
@@ -83,7 +65,7 @@ class Transformer {
     sourceMap: SourceMap,
   ) => Promise<{code: string, map: SourceMap}>;
 
-  constructor(transformModulePath: string) {
+  constructor(transformModulePath: string, maxWorkerCount: number) {
     invariant(path.isAbsolute(transformModulePath), 'transform module path should be absolute');
     this._transformModulePath = transformModulePath;
 
@@ -91,6 +73,7 @@ class Transformer {
       require.resolve('./worker'),
       ['minify', 'transformAndExtractDependencies'],
       TRANSFORM_TIMEOUT_INTERVAL,
+      maxWorkerCount,
     );
     this._transform = denodeify(this._workers.transformAndExtractDependencies);
     this.minify = denodeify(this._workers.minify);

packages/metro-bundler/src/Resolver/index.js

@@ -37,6 +37,7 @@ type Options = {
   getTransformCacheKey: GetTransformCacheKey,
   globalTransformCache: ?GlobalTransformCache,
   hasteImpl?: HasteImpl,
+  maxWorkerCount: number,
   minifyCode: MinifyCode,
   platforms: Set<string>,
   polyfillModuleNames?: Array<string>,

packages/metro-bundler/src/node-haste/__tests__/DependencyGraph-test.js

@@ -112,7 +112,7 @@ describe('DependencyGraph', function() {
       platforms: new Set(['ios', 'android']),
       useWatchman: false,
       ignoreFilePath: () => false,
-      maxWorkers: 1,
+      maxWorkerCount: 1,
       moduleOptions: {cacheTransformResults: true},
       resetCache: true,
       transformCode: (module, sourceCode, transformOptions) => {

packages/metro-bundler/src/node-haste/index.js

@@ -24,8 +24,8 @@ const fs = require('fs');
 const getAssetDataFromName = require('./lib/getAssetDataFromName');
 const getInverseDependencies = require('./lib/getInverseDependencies');
 const getPlatformExtension = require('./lib/getPlatformExtension');
+const invariant = require('fbjs/lib/invariant');
 const isAbsolutePath = require('absolute-path');
-const os = require('os');
 const path = require('path');
 const replacePatterns = require('./lib/replacePatterns');
 const util = require('util');
@@ -58,7 +58,7 @@ type Options = {
   getTransformCacheKey: GetTransformCacheKey,
   globalTransformCache: ?GlobalTransformCache,
   ignoreFilePath: (filePath: string) => boolean,
-  maxWorkers: ?number,
+  maxWorkerCount: number,
   moduleOptions: ModuleOptions,
   platforms: Set<string>,
   preferNativePlatform: boolean,
@@ -87,6 +87,7 @@ class DependencyGraph extends EventEmitter {
     initialModuleMap: ModuleMap,
   }) {
     super();
+    invariant(config.opts.maxWorkerCount >= 1, 'worker count must be greater or equal to 1');
     this._opts = config.opts;
     this._haste = config.haste;
     this._hasteFS = config.initialHasteFS;
@@ -97,12 +98,11 @@ class DependencyGraph extends EventEmitter {
   }
 
   static _createHaste(opts: Options): JestHasteMap {
-    const mw = opts.maxWorkers;
     return new JestHasteMap({
       extensions: opts.extensions.concat(opts.assetExts),
       forceNodeFilesystemAPI: opts.forceNodeFilesystemAPI,
       ignorePattern: {test: opts.ignoreFilePath},
-      maxWorkers: typeof mw === 'number' && mw >= 1 ? mw : getMaxWorkers(),
+      maxWorkers: opts.maxWorkerCount,
       mocksPattern: '',
       name: 'react-native-packager',
       platforms: Array.from(opts.platforms),
@@ -306,28 +306,4 @@ function NotFoundError() {
 }
 util.inherits(NotFoundError, Error);
 
-function getMaxWorkers() {
-  const cores = os.cpus().length;
-
-  if (cores <= 1) {
-    // oh well...
-    return 1;
-  }
-  if (cores <= 4) {
-    // don't starve the CPU while still reading reasonably rapidly
-    return cores - 1;
-  }
-  if (cores <= 8) {
-    // empirical testing showed massive diminishing returns when going over
-    // 4 or 5 workers on 8-core machines
-    return Math.floor(cores * 0.75) - 1;
-  }
-
-  // pretty much guesswork
-  if (cores < 24) {
-    return Math.floor(3 / 8 * cores + 3);
-  }
-  return cores / 2;
-}
-
 module.exports = DependencyGraph;