From d41a6b1d3591eb4c366f1543aab9bed866599aa6 Mon Sep 17 00:00:00 2001
From: Eugene Nikanorov <enikanorov@mirantis.com>
Date: Sat, 16 Mar 2013 17:53:39 +0400
Subject: [PATCH] Synchronize QuantumManager.get_instance() method

fixes bug 1155667

Change-Id: Ib6316b332fbd08c5b39e9820e5dc45f1846817cd
---
 quantum/manager.py | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/quantum/manager.py b/quantum/manager.py
index 74057dc5f..c7cc8a13e 100644
--- a/quantum/manager.py
+++ b/quantum/manager.py
@@ -20,6 +20,7 @@ from oslo.config import cfg
 
 from quantum.common.exceptions import ClassNotFound
 from quantum.openstack.common import importutils
+from quantum.openstack.common import lockutils
 from quantum.openstack.common import log as logging
 from quantum.openstack.common import periodic_task
 from quantum.plugins.common import constants
@@ -131,9 +132,16 @@ class QuantumManager(object):
                        "desc": plugin_inst.get_plugin_description()})
 
     @classmethod
-    def get_instance(cls):
+    @lockutils.synchronized("qmlock", "qml-")
+    def _create_instance(cls):
         if cls._instance is None:
             cls._instance = cls()
+
+    @classmethod
+    def get_instance(cls):
+        # double checked locking
+        if cls._instance is None:
+            cls._create_instance()
         return cls._instance
 
     @classmethod