refactor(cursor): remove dependency on async.times()

Re: #8073
Re: #5502

Author: Valeri Karpov

lib/helpers/cursor/eachAsync.js

@@ -38,18 +38,25 @@ module.exports = function eachAsync(next, fn, options, callback) {
   const iterate = function(callback) {
     let drained = false;
     const nextQueue = async.queue(function(task, cb) {
-      if (drained) return cb();
+      if (drained) {
+        return cb();
+      }
       next(function(err, doc) {
         if (err) return cb(err);
-        if (!doc) drained = true;
         cb(null, doc);
       });
     }, 1);
 
     const getAndRun = function(cb) {
       nextQueue.push({}, function(err, doc) {
         if (err) return cb(err);
-        if (!doc) return cb();
+        if (drained) {
+          return;
+        }
+        if (doc == null) {
+          drained = true;
+          return callback(null);
+        }
         handleNextResult(doc, function(err) {
           if (err) return cb(err);
           // Make sure to clear the stack re: gh-4697
@@ -60,9 +67,18 @@ module.exports = function eachAsync(next, fn, options, callback) {
       });
     };
 
-    async.times(parallel, function(n, cb) {
-      getAndRun(cb);
-    }, callback);
+    let error = null;
+    for (let i = 0; i < parallel; ++i) {
+      getAndRun(err => {
+        if (error != null) {
+          return;
+        }
+        if (err != null) {
+          error = err;
+          return callback(err);
+        }
+      });
+    }
   };
 
   return utils.promiseOrCallback(callback, cb => {

test/aggregate.test.js

@@ -1288,10 +1288,10 @@ describe('aggregate: ', function() {
         return MyModel.aggregate([{ $sort: { name: 1 } }]).
           cursor().
           exec().
-          eachAsync(checkDoc, { parallel: 2}).then(function() {
+          eachAsync(checkDoc, { parallel: 2 }).then(function() {
             assert.ok(Date.now() - startedAt[1] >= 100);
             assert.equal(startedAt.length, 2);
-            assert.ok(startedAt[1] - startedAt[0] < 50);
+            assert.ok(startedAt[1] - startedAt[0] < 50, `${startedAt[1] - startedAt[0]}`);
             assert.deepEqual(names.sort(), expectedNames);
             done();
           });