Improve fix issue 57

README.md

@@ -228,6 +228,11 @@ These let you tweak the default behavior.
 Most often, you'll just be setting the `cache_duration`
 to enable result caching.
 
+#### always_start_new_herd
+
+Skip herd avoidance check if True, but still trigger avoidance for other tasks.
+Defaults to False.
+
 #### cache_duration
 
 If you want your results cached,

jobtastic/task.py

@@ -82,6 +82,7 @@ class JobtasticTask(Task):
       front-end code so that users know what to expect.
     """
     abstract = True
+    always_start_new_herd = False
 
     #: The shared cache used for locking and thundering herd protection
     _cache = None
@@ -222,7 +223,20 @@ def apply_async(self, args, kwargs, **options):
         task_id = self.cache.get('herd:%s' % cache_key)
         if task_id:
             logging.info('Found existing in-progress task: %s', task_id)
-            return self.AsyncResult(task_id)
+            result = self.AsyncResult(task_id)
+            if not self.always_start_new_herd:
+                return result
+            if not result.ready():
+                logging.info(
+                    'Revoking in-progress task and starting new herd: %s',
+                    task_id,
+                )
+                result.revoke()
+            else:
+                logging.info(
+                    'Ignoring in-progress task and starting new herd: %s',
+                    task_id,
+                )
 
         # It's not cached and it's not already running. Use an atomic lock to
         # start the task, ensuring there isn't a race condition that could