packager: BatchProcessor: use Promise for queue()

Reviewed By: cpojer

Differential Revision: D4572181

fbshipit-source-id: 34c3824f05efd93847df9ba5931b0735c6711c28

packages/metro-bundler/src/lib/BatchProcessor.js

@@ -24,6 +24,12 @@ type BatchProcessorOptions = {
   concurrency: number,
 };
 
+type QueueItem<TItem, TResult> = {
+  item: TItem,
+  reject: (error: mixed) => mixed,
+  resolve: (result: TResult) => mixed,
+};
+
 /**
  * We batch items together trying to minimize their processing, for example as
  * network queries. For that we wait a small moment before processing a batch.
@@ -33,14 +39,11 @@ type BatchProcessorOptions = {
  */
 class BatchProcessor<TItem, TResult> {
 
+  _currentProcessCount: number;
   _options: BatchProcessorOptions;
   _processBatch: ProcessBatch<TItem, TResult>;
-  _queue: Array<{
-    item: TItem,
-    callback: (error?: Error, result?: TResult) => mixed,
-  }>;
+  _queue: Array<QueueItem<TItem, TResult>>;
   _timeoutHandle: ?number;
-  _currentProcessCount: number;
 
   constructor(
     options: BatchProcessorOptions,
@@ -64,12 +67,16 @@ class BatchProcessor<TItem, TResult> {
       const jobs = this._queue.splice(0, this._options.maximumItems);
       const items = jobs.map(job => job.item);
       this._processBatch(items, (error, results) => {
-        invariant(
-          results == null || results.length === items.length,
-          'Not enough results returned.',
-        );
-        for (let i = 0; i < items.length; ++i) {
-          jobs[i].callback(error, results && results[i]);
+        if (error != null) {
+          for (let i = 0; i < jobs.length; ++i) {
+            jobs[i].reject(error);
+          }
+        } else {
+          invariant(results != null, 'Neither results or error were returned.');
+          invariant(results.length === items.length, 'Not enough results returned.');
+          for (let i = 0; i < jobs.length; ++i) {
+            jobs[i].resolve(results[i]);
+          }
         }
         this._currentProcessCount--;
         this._processQueueOnceReady();
@@ -91,12 +98,11 @@ class BatchProcessor<TItem, TResult> {
     }
   }
 
-  queue(
-    item: TItem,
-    callback: (error?: Error, result?: TResult) => mixed,
-  ) {
-    this._queue.push({item, callback});
-    this._processQueueOnceReady();
+  queue(item: TItem): Promise<TResult> {
+    return new Promise((resolve, reject) => {
+      this._queue.push({item, resolve, reject});
+      this._processQueueOnceReady();
+    });
   }
 
 }

packages/metro-bundler/src/lib/GlobalTransformCache.js

@@ -74,7 +74,10 @@ class KeyURIFetcher {
   }
 
   fetch(key: string, callback: FetchURICallback) {
-    this._batchProcessor.queue(key, callback);
+    this._batchProcessor.queue(key).then(
+      res => process.nextTick(callback.bind(undefined, undefined, res)),
+      err => process.nextTick(callback.bind(undefined, err)),
+    );
   }
 
   constructor(fetchResultURIs: FetchResultURIs, processError: (error: Error) => mixed) {
@@ -107,7 +110,7 @@ class KeyResultStore {
   }
 
   store(key: string, result: CachedResult) {
-    this._batchProcessor.queue({key, result}, () => {});
+    this._batchProcessor.queue({key, result});
   }
 
   constructor(storeResults: StoreResults) {

packages/metro-bundler/src/lib/__mocks__/BatchProcessor.js

@@ -1,40 +0,0 @@
-/**
- * Copyright (c) 2015-present, Facebook, Inc.
- * All rights reserved.
- *
- * This source code is licensed under the BSD-style license found in the
- * LICENSE file in the root directory of this source tree. An additional grant
- * of patent rights can be found in the PATENTS file in the same directory.
- */
-
-'use strict';
-
-const {EventEmitter} = require('events');
-
-class BatchProcessorMock {
-
-  constructor(_, processBatch) {
-    this._processBatch = processBatch;
-    this._queue = [];
-    BatchProcessorMock.mocks.emit('new', this);
-  }
-
-  queue(item, callback) {
-    this._queue.push([item, callback]);
-  }
-
-  flushMock() {
-    const {_queue} = this;
-    this._queue = [];
-    process.nextTick(() => {
-      this._processBatch(_queue.map(pair => pair[0]), (error, res) => {
-        _queue.forEach((pair, i) => pair[1](error, res && res[i]));
-      });
-    });
-  }
-
-}
-
-BatchProcessorMock.mocks = new EventEmitter();
-
-module.exports = BatchProcessorMock;

packages/metro-bundler/src/lib/__tests__/BatchProcessor-test.js

@@ -38,12 +38,12 @@ describe('BatchProcessor', () => {
       }, 0);
     });
     const results = [];
-    const callback = (error, res) => {
-      expect(error).toBe(null);
-      results.push(res);
-    };
-    input.forEach(e => bp.queue(e, callback));
+    input.forEach(e => bp.queue(e).then(
+      res => results.push(res),
+      error => process.nextTick(() => { throw error; }),
+    ));
     jest.runAllTimers();
+    jest.runAllTicks();
     expect(batches).toEqual([
       [1, 2, 3],
       [4, 5, 6],
@@ -56,10 +56,12 @@ describe('BatchProcessor', () => {
   it('report errors', () => {
     const error = new Error('oh noes');
     const bp = new BatchProcessor(options, (items, callback) => {
-      process.nextTick(callback.bind(null, error));
+      setTimeout(callback.bind(null, error), 0);
     });
     let receivedError;
-    bp.queue('foo', err => { receivedError = err; });
+    bp.queue('foo').catch(
+      err => { receivedError = err; },
+    );
     jest.runAllTimers();
     jest.runAllTicks();
     expect(receivedError).toBe(error);