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

2 files changed, 48 insertions, 7 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."""
diff --git a/nova/tests/unit/servicegroup/test_zk_driver.py b/nova/tests/unit/servicegroup/test_zk_driver.py
index 08121c8290..ddd3073b97 100644
--- a/nova/tests/unit/servicegroup/test_zk_driver.py
+++ b/nova/tests/unit/servicegroup/test_zk_driver.py
@@ -29,6 +29,7 @@ import os
 import eventlet
 
 from nova import servicegroup
+from nova.servicegroup.drivers import zk
 from nova import test
 
 
@@ -37,7 +38,6 @@ class ZKServiceGroupTestCase(test.NoDBTestCase):
     def setUp(self):
         super(ZKServiceGroupTestCase, self).setUp()
         servicegroup.API._driver = None
-        from nova.servicegroup.drivers import zk
         self.flags(servicegroup_driver='zk')
         self.flags(address='localhost:2181', group="zookeeper")
         try:
@@ -85,3 +85,18 @@ class ZKServiceGroupTestCase(test.NoDBTestCase):
                                    None)
         # expected existing "process id" node
         self.assertTrue(session.get(path))
+
+    def test_lazy_session(self):
+        """Session object (contains zk handle) should be created in
+        lazy manner, because handle cannot be shared by forked processes.
+        """
+        # insied import because this test runs conditionaly (look at setUp)
+        import evzookeeper
+        driver = zk.ZooKeeperDriver()
+        # check that internal private attribute session is empty
+        self.assertIsNone(driver.__dict__['_ZooKeeperDriver__session'])
+        # after first use of property ...
+        driver._session
+        # check that internal private session attribute is ready
+        self.assertIsInstance(driver.__dict__['_ZooKeeperDriver__session'],
+                              evzookeeper.ZKSession)