Proof of concept Redis PubSub.

awx/main/management/commands/run_task_system.py

@@ -251,7 +251,9 @@ def process_graph(graph, task_capacity):
             print("Started Node: %s (capacity hit: %s) Remaining Capacity: %s" % (str(node_obj), str(impact), str(remaining_volume)))
 
 def run_taskmanager(command_port):
-    ''' Receive task start and finish signals to rebuild a dependency graph and manage the actual running of tasks '''
+    """Receive task start and finish signals to rebuild a dependency graph
+    and manage the actual running of tasks.
+    """
     def shutdown_handler():
         def _handler(signum, frame):
             signal.signal(signum, signal.SIG_DFL)

awx/main/queue.py

@@ -28,3 +28,51 @@ class FifoQueue(object):
         """Retrieve a value from the left side of the queue."""
         return json.loads(redis.lpop(self._queue_name))
 
+
+class PubSub(object):
+    """An abstraction class implemented for pubsub.
+
+    Intended to allow alteration of backend details in a single, consistent
+    way throughout the Tower application.
+    """
+    def __init__(self, queue_name):
+        """Instantiate a pubsub object, which is able to interact with a
+        Redis key as a pubsub.
+
+        Ideally this should be used with `contextmanager.closing` to ensure
+        well-behavedness:
+
+            from contextmanager import closing
+
+            with closing(PubSub('foobar')) as foobar:
+                for message in foobar.listen(wait=0.1):
+                    <deal with message>
+        """
+        self._queue_name = queue_name
+        self._ps = redis.pubsub(ignore_subscribe_messages=True)
+        self._ps.subscribe(queue_name)
+
+    def publish(self, message):
+        """Publish a message to the given queue."""
+        redis.publish(self._queue_name, json.dumps(message))
+
+    def retrieve(self):
+        """Retrieve a single message from the subcription channel
+        and return it.
+        """
+        return self._ps.get_message()
+
+    def listen(self, wait=0.001):
+        """Listen to content from the subscription channel indefinitely,
+        and yield messages as they are retrieved.
+        """
+        while True:
+            message = self.retrieve()
+            if message is None:
+                time.sleep(max(wait, 0.001))
+            else:
+                yield json.loads(message)
+
+    def close(self):
+        """Close the pubsub connection."""
+        self._ps.close()