Don't reload config when file wasn't modified

The launcher thread will reload the config in the main loop every second
(watermark sleep) without checking if the config changed. This can take
quite a bit of CPU time as we've seen from different Yappi profiles.

This change uses the last modified timestamp of the config file to
detect if the Nodepool config needs to be reloaded.

The test `test_nodepool_occ_config_reload` was changed to update the
provider config so that a new OpenStack client object is created.

Change-Id: I93400cc156d09ea1add4fc753846df923242c0e6

nodepool/launcher.py

@@ -1029,7 +1029,9 @@ class NodePool(threading.Thread):
                  watermark_sleep=WATERMARK_SLEEP):
         threading.Thread.__init__(self, name='NodePool')
         self.securefile = securefile
+        self._secure_mtime = 0
         self.configfile = configfile
+        self._config_mtime = 0
         self.watermark_sleep = watermark_sleep
         self.cleanup_interval = 60
         self.delete_interval = 5
@@ -1134,6 +1136,16 @@ class NodePool(threading.Thread):
                 t.provider_name == provider_name]
 
     def updateConfig(self):
+        secure_mtime = 0
+        config_mtime = os.stat(self.configfile).st_mtime_ns
+        if self._config_mtime == config_mtime:
+            if self.securefile:
+                secure_mtime = os.stat(self.securefile).st_mtime_ns
+                if self._secure_mtime == secure_mtime:
+                    return
+            else:
+                return
+
         config = self.loadConfig()
         self.reconfigureZooKeeper(config)
         provider_manager.ProviderManager.reconfigure(self.config, config,
@@ -1141,7 +1153,10 @@ class NodePool(threading.Thread):
         for provider_name in list(config.providers.keys()):
             if provider_name not in config.provider_managers:
                 del config.providers[provider_name]
+
         self.setConfig(config)
+        self._config_mtime = config_mtime
+        self._secure_mtime = secure_mtime
 
     def removeCompletedRequests(self):
         '''

nodepool/tests/unit/test_sdk_integration.py

@@ -85,6 +85,14 @@ class TestShadeIntegration(tests.IntegrationTestCase):
         with open(self.clouds_path, 'w') as h:
             yaml.safe_dump(occ_config, h)
 
+        # Change the provider to force a new OpenStack client object
+        # to be created.
+        with open(configfile) as f:
+            config = yaml.safe_load(f)
+        config['providers'][0]['rate'] = 0.0002
+        with open(configfile, 'w') as f:
+            yaml.safe_dump(config, f)
+
         pool.updateConfig()
         pm = pool.config.provider_managers['real-provider']
         self.assertEqual(pm.adapter._client.auth, auth_data)