Adds kombu.common.maybe_declare: To only declare entity if not already declared in current connection

kombu/common.py

@@ -1,5 +1,44 @@
+from collections import defaultdict
+
 from kombu import entity
-from kombu.utils import gen_unique_id as uuid
+from kombu.utils import uuid
+
+declared_entities = defaultdict(lambda: set())
+
+
+def maybe_declare(entity, channel):
+    declared = declared_entities[channel.connection.client]
+    if not entity.is_bound:
+        entity = entity(channel)
+    if entity not in declared:
+        entity.declare()
+        declared.add(entity)
+        return True
+    return False
+
+
+class Broadcast(entity.Queue):
+    """Convenience class used to define broadcast queues.
+
+    Every queue instance will have a unique name,
+    and both the queue and exchange is configued with auto deletion.
+
+    :keyword name: This is used as the name of the exchange.
+    :keyword queue: By default a unique id is used for the queue
+       name for every consumer.  You can specify a custom queue
+       name here.
+    :keyword \*\*kwargs: See :class:`~kombu.entity.Queue` for a list
+        of additional keyword arguments supported.
+
+    """
+
+    def __init__(self, name=None, queue=None, **kwargs):
+        kwargs.setdefault("exchange", entity.Exchange(name, type="fanout",
+                                                      auto_delete=True))
+        kwargs.setdefault("auto_delete", True)
+        kwargs.setdefault("alias", name)
+        return super(Broadcast, self).__init__(
+                name=queue or "bcast.%s" % (uuid(), ), **kwargs)
 
 
 def entry_to_queue(queue, **options):