Scheduler handles new tasks when there is free slots

batch/scheduler/scheduler.js

@@ -64,6 +64,8 @@ Scheduler.prototype.add = function(user) {
         this.users[user] = taskEntity;
         this.tasksTree.insert(taskEntity);
 
+        this.emit('add');
+
         return false;
     }
 };
@@ -122,19 +124,33 @@ Scheduler.prototype.acquire = function(callback) {
             return callback(err);
         }
 
+        function addListener() {
+            self.removeListener('release', releaseListener);
+            debug('Got a new task');
+            self.acquire(callback);
+        }
+
+        function releaseListener() {
+            self.removeListener('add', addListener);
+            debug('Slot was released');
+            self.acquire(callback);
+        }
+
         debug('Trying to acquire task');
 
         var allRunning = self.tasks.every(is(STATUS.RUNNING));
         var running = self.tasks.filter(is(STATUS.RUNNING));
         debug('[capacity=%d, running=%d, all=%s] candidates=%j', capacity, running.length, allRunning, self.tasks);
 
+        if (allRunning && running.length < capacity) {
+            debug('Waiting for tasks');
+            self.once('add', addListener);
+        }
+
         var isRunningAny = self.tasks.some(is(STATUS.RUNNING));
         if (isRunningAny || running.length >= capacity) {
             debug('Waiting for slot');
-            return self.once('release', function releaseListener() {
-                debug('Slot was released');
-                self.acquire(callback);
-            });
+            return self.once('release', releaseListener);
         }
 
         var candidate = self.tasksTree.min();