Avoid duplication of discovery for multi-sink sources

Perviously, where a single source has a pluggable discovery
extension loaded and is associated with multiple sinks, the
discovered resources were duplicated for each sink.

Now, we ensure that duplicate discovery extensions are
excluded.

Change-Id: Icffcc65f2be2baef7730b31773b39ffdda0454a7
Closes-Bug: #1354536

ceilometer/agent.py

@@ -37,11 +37,11 @@ class Resources(object):
     def __init__(self, agent_manager):
         self.agent_manager = agent_manager
         self._resources = []
-        self._discovery = []
+        self._discovery = set([])
 
     def extend(self, pipeline):
         self._resources.extend(pipeline.resources)
-        self._discovery.extend(pipeline.discovery)
+        self._discovery.update(set(pipeline.discovery))
 
     @property
     def resources(self):

ceilometer/tests/agentbase.py

@@ -520,3 +520,27 @@ class BaseAgentManagerTestCase(base.BaseTestCase):
         self.assertEqual(1, len(self.PollsterAnother.samples))
         self.assertEqual(['discovered_3', 'discovered_4'],
                          self.PollsterAnother.resources)
+
+    def test_multiple_sinks_same_discoverer(self):
+        self.Discovery.resources = ['discovered_1', 'discovered_2']
+        sources = [{'name': 'test_source_1',
+                    'interval': 60,
+                    'counters': ['test'],
+                    'discovery': ['testdiscovery'],
+                    'sinks': ['test_sink_1', 'test_sink_2']}]
+        sinks = [{'name': 'test_sink_1',
+                  'transformers': [],
+                  'publishers': ['test://']},
+                 {'name': 'test_sink_2',
+                  'transformers': [],
+                  'publishers': ['test://']}]
+        self.pipeline_cfg = {'sources': sources, 'sinks': sinks}
+        self.mgr.discovery_manager = self.create_discovery_manager()
+        self.setup_pipeline()
+        polling_tasks = self.mgr.setup_polling_tasks()
+        self.assertEqual(1, len(polling_tasks))
+        self.assertTrue(60 in polling_tasks.keys())
+        self.mgr.interval_task(polling_tasks.get(60))
+        self.assertEqual(1, len(self.Pollster.samples))
+        self.assertEqual(['discovered_1', 'discovered_2'],
+                         self.Pollster.resources)