Applied work function locking for multi_caching

lib/multi_caching.js

@@ -7,6 +7,8 @@ var multi_caching = function (caches) {
     var self = {};
     if (!Array.isArray(caches)) { throw new Error('multi_caching requires an array of caches'); }
 
+    self.queues = {};
+
     function get_from_highest_priority_cache(key, cb) {
         var i = 0;
         async.forEachSeries(caches, function (cache, async_cb) {
@@ -41,21 +43,38 @@ var multi_caching = function (caches) {
      */
     self.wrap = function (key, work, cb) {
         get_from_highest_priority_cache(key, function (err, result, index) {
-            if (err) { return cb(err); }
-            if (result) {
+            if (err) {
+                return cb(err);
+            } else if (result) {
                 var caches_to_update = caches.slice(0, index);
                 set_in_multiple_caches(caches_to_update, key, result, function (err) {
                     cb(err, result);
                 });
+            } else if (self.queues[key]) {
+                self.queues[key].push(cb);
             } else {
+                self.queues[key] = [cb];
                 work(function () {
                     var work_args = Array.prototype.slice.call(arguments, 0);
                     if (work_args[0]) { // assume first arg is an error
-                        return cb(work_args[0]);
+                        self.queues[key].forEach(function (done) {
+                            done.call(null, work_args[0]);
+                        });
+                        delete self.queues[key];
+                        return;
                     }
                     set_in_multiple_caches(caches, key, work_args[1], function (err) {
-                        if (err) { return cb(err); }
-                        cb.apply(null, work_args);
+                        if (err) {
+                            self.queues[key].forEach(function (done) {
+                                done.call(null, err);
+                            });
+                            delete self.queues[key];
+                            return;
+                        }
+                        self.queues[key].forEach(function (done) {
+                            done.apply(null, work_args);
+                        });
+                        delete self.queues[key];
                     });
                 });
             }