Merge "Fix conductor servicegroup joining when zk driver is used"

1 files changed, 32 insertions, 6 deletions

diff --git a/nova/servicegroup/drivers/zk.py b/nova/servicegroup/drivers/zk.py
index b391d173f5..6a06bf24b6 100644
--- a/nova/servicegroup/drivers/zk.py
+++ b/nova/servicegroup/drivers/zk.py
@@ -59,21 +59,47 @@ class ZooKeeperDriver(base.Driver):
         """Create the zk session object."""
         if not all([evzookeeper, membership, zookeeper]):
             raise ImportError('zookeeper module not found')
+        self._memberships = {}
+        self._monitors = {}
+        super(ZooKeeperDriver, self).__init__()
+        self._cached_session = None
+
+    @property
+    def _session(self):
+        """Creates zookeeper session in lazy manner.
+
+        Session is created in lazy manner to mitigate lock problem
+        in zookeeper.
+
+        Lock happens when many processes try to use the same zk handle.
+        Lazy creation allows to deffer initialization of session until
+        is really required by worker (child process).
+
+        :returns: ZKSession -- new or created earlier
+        """
+        if self._cached_session is None:
+            self._cached_session = self._init_session()
+        return self._cached_session
+
+    def _init_session(self):
+        """Initializes new session.
+
+        Optionally creates required servicegroup prefix.
+
+        :returns ZKSession - newly created session
+        """
         null = open(os.devnull, "w")
-        self._session = evzookeeper.ZKSession(CONF.zookeeper.address,
+        session = evzookeeper.ZKSession(CONF.zookeeper.address,
                                               recv_timeout=
                                                 CONF.zookeeper.recv_timeout,
                                               zklog_fd=null)
-        self._memberships = {}
-        self._monitors = {}
         # Make sure the prefix exists
         try:
-            self._session.create(CONF.zookeeper.sg_prefix, "",
+            session.create(CONF.zookeeper.sg_prefix, "",
                                  acl=[evzookeeper.ZOO_OPEN_ACL_UNSAFE])
         except zookeeper.NodeExistsException:
             pass
-
-        super(ZooKeeperDriver, self).__init__()
+        return session
 
     def join(self, member_id, group, service=None):
         """Join the given service with its group."""