diff --git a/jtracker/gitracker.py b/jtracker/gitracker.py
index 2472307..10c7888 100644
--- a/jtracker/gitracker.py
+++ b/jtracker/gitracker.py
@@ -375,20 +375,53 @@ def _check_task_dependency(self, worker=None, task_json=None, task_dict=None, jo
         worker_id = worker.worker_id
         host_id = worker.host_id
 
-        depends_on = task_dict.get('depends_on')
-        if not depends_on: return True
-
         # constraint can be 'same_host', 'same_worker', 'shared_fs' or None
         constraint = self.workflow.workflow_dict.get('workflow',{}).get('execution',{}).get('constraint')
 
+        depends_on = task_dict.get('depends_on')
+        if not depends_on:
+            # if there is no task running for this job, and this task does not have depends_on
+            # then start it.
+            started_tasks = []
+            for t_state in (TASK_STATE.RUNNING, TASK_STATE.COMPLETED, TASK_STATE.FAILED):
+                path_to_task = os.path.join(
+                                                self.gitracker_home,
+                                                JOB_STATE.RUNNING,
+                                                job_id,
+                                                t_state,
+                                                'worker.*',
+                                                'task.*',
+                                                'task.*.json'
+                                            )
+                started_tasks += glob.glob(path_to_task)
+
+            if not started_tasks:
+                return True  # this is the first task to run
+            else:
+                one_started_worker_id = started_tasks[0].split(os.path.sep)[-3]
+                if constraint == 'same_worker':
+                    if worker_id == one_started_worker_id:
+                        return True
+                    else:
+                        return False
+                elif constraint == 'same_host':
+                    if worker_id.split('.host.')[-1] == one_started_worker_id.split('.host.')[-1]:
+                        return True  # this worker is on the same host
+                    else:
+                        return False
+                elif constraint == 'shared_fs':
+                    # need more thoughts here, for now 'shared_fs' means no constraint
+                    # all worker on all host can access the same shared file system
+                    return True
+                else:
+                    return False  # constraint must set, otherwise won't run
+
         worker_id_pattern = 'worker.*'
-        """
         ## to be implemented properly, for now every worker can run a task
         if constraint and constraint == 'same_worker':
             worker_id_pattern = worker_id
         elif constraint and constraint == 'same_host':  # more work is needed to handle tasks do not have dependencies, they will run without checking host
             worker_id_pattern = 'worker.*.host.%s.*' % host_id
-        """
 
         # we will need better implementation, consider covering 'failed' parent task as well
         # right now it only check whether parent task state is COMPLETED
@@ -414,7 +447,6 @@ def _check_task_dependency(self, worker=None, task_json=None, task_dict=None, jo
                                                     'task.%s.*.json' % parent_task
                                                 )
             if glob.glob(path_to_parent_task1_in_queue) + glob.glob(path_to_parent_task2_in_queue):
-                print glob.glob(path_to_parent_task2_in_queue)
                 return False
 
             # non scatter task