From 5ea4484a2ca2b323ddb3c1561296be18ea80a16d Mon Sep 17 00:00:00 2001
From: Russell Haering <russell.haering@rackspace.com>
Date: Wed, 22 Jan 2014 17:28:24 -0800
Subject: [PATCH] cache a global hardware manager

---
 teeth_agent/agent.py    |  4 ++--
 teeth_agent/hardware.py | 34 ++++++++++++++++++++--------------
 2 files changed, 22 insertions(+), 16 deletions(-)

diff --git a/teeth_agent/agent.py b/teeth_agent/agent.py
index 718f2b436..efad3d12e 100644
--- a/teeth_agent/agent.py
+++ b/teeth_agent/agent.py
@@ -118,7 +118,7 @@ class TeethAgent(object):
         self.api = api.TeethAgentAPIServer(self)
         self.command_results = collections.OrderedDict()
         self.heartbeater = TeethAgentHeartbeater(self)
-        self.hardware = hardware.load_hardware_manager()
+        self.hardware = hardware.get_manager()
         self.command_lock = threading.Lock()
         self.log = structlog.get_logger()
         self.started_at = None
@@ -235,7 +235,7 @@ def build_agent(api_url,
     if not listen_host:
         listen_host = advertise_host
 
-    mac_addr = hardware.load_hardware_manager().get_primary_mac_address()
+    mac_addr = hardware.get_manager().get_primary_mac_address()
     api_client = overlord_agent_api.APIClient(api_url)
 
     log.info('fetching agent configuration from API',
diff --git a/teeth_agent/hardware.py b/teeth_agent/hardware.py
index 5dfc56940..b747180cd 100644
--- a/teeth_agent/hardware.py
+++ b/teeth_agent/hardware.py
@@ -59,20 +59,26 @@ def _compare_extensions(ext1, ext2):
     return mgr1.evaluate_hardware_support() - mgr2.evaluate_hardware_support()
 
 
-def load_hardware_manager():
-    log = structlog.get_logger()
-    extension_manager = stevedore.ExtensionManager(
-        namespace='teeth_agent.hardware_managers',
-        invoke_on_load=True)
+def get_manager():
+    global _global_manager
 
-    # There will always be at least one extension available (the
-    # GenericHardwareManager).
-    preferred_extension = sorted(extension_manager, _compare_extensions)[0]
-    preferred_manager = preferred_extension.obj
+    if not _global_manager:
+        log = structlog.get_logger()
+        extension_manager = stevedore.ExtensionManager(
+            namespace='teeth_agent.hardware_managers',
+            invoke_on_load=True)
 
-    if preferred_manager.evaluate_hardware_support() <= 0:
-        raise RuntimeError('No suitable HardwareManager could be found')
+        # There will always be at least one extension available (the
+        # GenericHardwareManager).
+        preferred_extension = sorted(extension_manager, _compare_extensions)[0]
+        preferred_manager = preferred_extension.obj
 
-    log.info('selected hardware manager',
-             manager_name=preferred_extension.entry_point_target)
-    return preferred_manager
+        if preferred_manager.evaluate_hardware_support() <= 0:
+            raise RuntimeError('No suitable HardwareManager could be found')
+
+        log.info('selected hardware manager',
+                 manager_name=preferred_extension.entry_point_target)
+
+        _global_manager = preferred_manager
+
+    return _global_manager