Improve Fast Refresh responsiveness when watching a large number of files (#913)

Summary:
Pull Request resolved: #913

Following D40829941 (7191173), where we changed the output of `metro-file-map`'s `build()` to return "live" references to the file system and the Haste module map (rather than snapshots), we no longer require further snapshots to be emitted as part of a change event payload. In fact, `ChangeEvent['snapshotFS']` and `ChangeEvent['moduleMap']` are currently only referenced in test code.

Removing them means we don't have to copy potentially large data structures on each emitted change.

With ~300k files and ~150k Haste map entries, this amounts to ~200ms more responsive fast refresh - in general this boost will be proportional to the total number of files+Haste modules watched.

After this, a `HasteFS` instance is only constructed once, on Metro startup. That clears the way for an alternative (more expensive to initialise) implementation capable of performing lookups through symlinks.

Changelog: [Performance] Improve Fast Refresh responsiveness when watching a large number of files.

Reviewed By: motiz88

Differential Revision: D42303139

fbshipit-source-id: b158ca2fdcddf02ecb2f2d17bc5b35e448fed0ae

Author: robhogan

packages/metro-file-map/src/__tests__/index-test.js

@@ -1364,13 +1364,13 @@ describe('HasteMap', () => {
     }
 
     hm_it('build returns a "live" fileSystem and hasteModuleMap', async hm => {
-      const initialResult = await hm.build();
+      const {fileSystem, hasteModuleMap} = await hm.build();
       const filePath = path.join('/', 'project', 'fruits', 'Banana.js');
-      expect(initialResult.fileSystem.getModuleName(filePath)).toBeDefined();
-      expect(initialResult.hasteModuleMap.getModule('Banana')).toBe(filePath);
+      expect(fileSystem.getModuleName(filePath)).toBeDefined();
+      expect(hasteModuleMap.getModule('Banana')).toBe(filePath);
       mockDeleteFile(path.join('/', 'project', 'fruits'), 'Banana.js');
       mockDeleteFile(path.join('/', 'project', 'fruits'), 'Banana.js');
-      const {eventsQueue, snapshotFS, moduleMap} = await waitForItToChange(hm);
+      const {eventsQueue} = await waitForItToChange(hm);
       expect(eventsQueue).toHaveLength(1);
       const deletedBanana = {
         filePath,
@@ -1379,10 +1379,8 @@ describe('HasteMap', () => {
       };
       expect(eventsQueue).toEqual([deletedBanana]);
       // Verify that the initial result has been updated
-      expect(initialResult.fileSystem.getModuleName(filePath)).toBeNull();
-      expect(initialResult.hasteModuleMap.getModule('Banana')).toBeNull();
-      expect(snapshotFS.getModuleName(filePath)).toBeNull();
-      expect(moduleMap.getModule('Banana')).toBeNull();
+      expect(fileSystem.getModuleName(filePath)).toBeNull();
+      expect(hasteModuleMap.getModule('Banana')).toBeNull();
     });
 
     const MOCK_CHANGE_FILE = {
@@ -1398,6 +1396,7 @@ describe('HasteMap', () => {
     };
 
     hm_it('handles several change events at once', async hm => {
+      const {fileSystem, hasteModuleMap} = await hm.build();
       mockFs[path.join('/', 'project', 'fruits', 'Tomato.js')] = `
         // Tomato!
       `;
@@ -1419,7 +1418,7 @@ describe('HasteMap', () => {
         path.join('/', 'project', 'fruits'),
         MOCK_CHANGE_FILE,
       );
-      const {eventsQueue, snapshotFS, moduleMap} = await waitForItToChange(hm);
+      const {eventsQueue} = await waitForItToChange(hm);
       expect(eventsQueue).toEqual([
         {
           filePath: path.join('/', 'project', 'fruits', 'Tomato.js'),
@@ -1433,12 +1432,12 @@ describe('HasteMap', () => {
         },
       ]);
       expect(
-        snapshotFS.getModuleName(
+        fileSystem.getModuleName(
           path.join('/', 'project', 'fruits', 'Tomato.js'),
         ),
       ).not.toBeNull();
-      expect(moduleMap.getModule('Tomato')).toBeDefined();
-      expect(moduleMap.getModule('Pear')).toBe(
+      expect(hasteModuleMap.getModule('Tomato')).toBeDefined();
+      expect(hasteModuleMap.getModule('Pear')).toBe(
         path.join('/', 'project', 'fruits', 'Pear.js'),
       );
     });
@@ -1466,6 +1465,7 @@ describe('HasteMap', () => {
     hm_it(
       'emits a change even if a file in node_modules has changed',
       async hm => {
+        const {fileSystem} = await hm.build();
         const e = mockEmitters[path.join('/', 'project', 'fruits')];
         e.emit(
           'all',
@@ -1474,7 +1474,7 @@ describe('HasteMap', () => {
           path.join('/', 'project', 'fruits', 'node_modules', ''),
           MOCK_CHANGE_FILE,
         );
-        const {eventsQueue, snapshotFS} = await waitForItToChange(hm);
+        const {eventsQueue} = await waitForItToChange(hm);
         const filePath = path.join(
           '/',
           'project',
@@ -1486,16 +1486,16 @@ describe('HasteMap', () => {
         expect(eventsQueue).toEqual([
           {filePath, metadata: MOCK_CHANGE_FILE, type: 'add'},
         ]);
-        expect(snapshotFS.getModuleName(filePath)).toBeDefined();
+        expect(fileSystem.getModuleName(filePath)).toBeDefined();
       },
     );
 
     hm_it(
       'correctly tracks changes to both platform-specific versions of a single module name',
       async hm => {
-        const {hasteModuleMap: initMM} = await hm.build();
-        expect(initMM.getModule('Orange', 'ios')).toBeTruthy();
-        expect(initMM.getModule('Orange', 'android')).toBeTruthy();
+        const {hasteModuleMap, fileSystem} = await hm.build();
+        expect(hasteModuleMap.getModule('Orange', 'ios')).toBeTruthy();
+        expect(hasteModuleMap.getModule('Orange', 'android')).toBeTruthy();
         const e = mockEmitters[path.join('/', 'project', 'fruits')];
         e.emit(
           'all',
@@ -1511,9 +1511,7 @@ describe('HasteMap', () => {
           path.join('/', 'project', 'fruits'),
           MOCK_CHANGE_FILE,
         );
-        const {eventsQueue, snapshotFS, moduleMap} = await waitForItToChange(
-          hm,
-        );
+        const {eventsQueue} = await waitForItToChange(hm);
         expect(eventsQueue).toHaveLength(2);
         expect(eventsQueue).toEqual([
           {
@@ -1528,20 +1526,20 @@ describe('HasteMap', () => {
           },
         ]);
         expect(
-          snapshotFS.getModuleName(
+          fileSystem.getModuleName(
             path.join('/', 'project', 'fruits', 'Orange.ios.js'),
           ),
         ).toBeTruthy();
         expect(
-          snapshotFS.getModuleName(
+          fileSystem.getModuleName(
             path.join('/', 'project', 'fruits', 'Orange.android.js'),
           ),
         ).toBeTruthy();
-        const iosVariant = moduleMap.getModule('Orange', 'ios');
+        const iosVariant = hasteModuleMap.getModule('Orange', 'ios');
         expect(iosVariant).toBe(
           path.join('/', 'project', 'fruits', 'Orange.ios.js'),
         );
-        const androidVariant = moduleMap.getModule('Orange', 'android');
+        const androidVariant = hasteModuleMap.getModule('Orange', 'android');
         expect(androidVariant).toBe(
           path.join('/', 'project', 'fruits', 'Orange.android.js'),
         );
@@ -1560,6 +1558,7 @@ describe('HasteMap', () => {
 
     describe('recovery from duplicate module IDs', () => {
       async function setupDuplicates(hm) {
+        const {fileSystem, hasteModuleMap} = await hm.build();
         mockFs[path.join('/', 'project', 'fruits', 'Pear.js')] = `
           // Pear!
         `;
@@ -1581,14 +1580,14 @@ describe('HasteMap', () => {
           path.join('/', 'project', 'fruits', 'another'),
           MOCK_CHANGE_FILE,
         );
-        const {snapshotFS, moduleMap} = await waitForItToChange(hm);
+        await waitForItToChange(hm);
         expect(
-          snapshotFS.exists(
+          fileSystem.exists(
             path.join('/', 'project', 'fruits', 'another', 'Pear.js'),
           ),
         ).toBe(true);
         try {
-          moduleMap.getModule('Pear');
+          hasteModuleMap.getModule('Pear');
           throw new Error('should be unreachable');
         } catch (error) {
           const {
@@ -1612,6 +1611,7 @@ describe('HasteMap', () => {
       hm_it(
         'recovers when the oldest version of the duplicates is fixed',
         async hm => {
+          const {hasteModuleMap} = await hm.build();
           await setupDuplicates(hm);
           mockFs[path.join('/', 'project', 'fruits', 'Pear.js')] = null;
           mockFs[path.join('/', 'project', 'fruits', 'Pear2.js')] = `
@@ -1632,17 +1632,18 @@ describe('HasteMap', () => {
             path.join('/', 'project', 'fruits'),
             MOCK_CHANGE_FILE,
           );
-          const {moduleMap} = await waitForItToChange(hm);
-          expect(moduleMap.getModule('Pear')).toBe(
+          await waitForItToChange(hm);
+          expect(hasteModuleMap.getModule('Pear')).toBe(
             path.join('/', 'project', 'fruits', 'another', 'Pear.js'),
           );
-          expect(moduleMap.getModule('Pear2')).toBe(
+          expect(hasteModuleMap.getModule('Pear2')).toBe(
             path.join('/', 'project', 'fruits', 'Pear2.js'),
           );
         },
       );
 
       hm_it('recovers when the most recent duplicate is fixed', async hm => {
+        const {hasteModuleMap} = await hm.build();
         await setupDuplicates(hm);
         mockFs[path.join('/', 'project', 'fruits', 'another', 'Pear.js')] =
           null;
@@ -1664,11 +1665,11 @@ describe('HasteMap', () => {
           path.join('/', 'project', 'fruits', 'another'),
           MOCK_CHANGE_FILE,
         );
-        const {moduleMap} = await waitForItToChange(hm);
-        expect(moduleMap.getModule('Pear')).toBe(
+        await waitForItToChange(hm);
+        expect(hasteModuleMap.getModule('Pear')).toBe(
           path.join('/', 'project', 'fruits', 'Pear.js'),
         );
-        expect(moduleMap.getModule('Pear2')).toBe(
+        expect(hasteModuleMap.getModule('Pear2')).toBe(
           path.join('/', 'project', 'fruits', 'another', 'Pear2.js'),
         );
       });

packages/metro-file-map/src/flow-types.js

@@ -59,8 +59,6 @@ export type CacheManagerFactory = (
 export type ChangeEvent = {
   logger: ?RootPerfLogger,
   eventsQueue: EventsQueue,
-  snapshotFS: FileSystem,
-  moduleMap: ModuleMap,
 };
 
 export type ChangeEventMetadata = {

packages/metro-file-map/src/index.js

@@ -799,25 +799,6 @@ export default class HasteMap extends EventEmitter {
     return this._worker;
   }
 
-  _getSnapshot(data: InternalData): {
-    snapshotFS: FileSystem,
-    moduleMap: HasteModuleMap,
-  } {
-    const rootDir = this._options.rootDir;
-    return {
-      snapshotFS: new HasteFS({
-        files: new Map(data.files),
-        rootDir,
-      }),
-      moduleMap: new HasteModuleMap({
-        duplicates: new Map(data.duplicates),
-        map: new Map(data.map),
-        mocks: new Map(data.mocks),
-        rootDir,
-      }),
-    };
-  }
-
   _removeIfExists(data: InternalData, relativeFilePath: Path) {
     const fileMetadata = data.files.get(relativeFilePath);
     if (!fileMetadata) {
@@ -900,7 +881,6 @@ export default class HasteMap extends EventEmitter {
         const changeEvent: ChangeEvent = {
           logger: hmrPerfLogger,
           eventsQueue,
-          ...this._getSnapshot(data),
         };
         this.emit('change', changeEvent);
         eventsQueue = [];