From ae74b483c3b9533d4f92d5b0b1210f35c896d2d2 Mon Sep 17 00:00:00 2001
From: Rodolfo Alonso Hernandez <ralonsoh@redhat.com>
Date: Tue, 2 Jun 2020 11:10:21 +0000
Subject: [PATCH] Make NeutronOvsdbIdl singleton

"NeutronOvsdbIdl" should be a singleton class; only one instance
should be shared everywhere is called. Currently the connection
and the "OvsIdlMonitor" instances are global; those instances are
used to declare the "NeutronOvsdbIdl" instance.

As commented in the related bug, this singleton will ensure that
the OvsIdl indexes are created just once.

Related-Bug: #1881424

Conflicts:
    neutron/common/utils.py
    neutron/agent/ovsdb/impl_idl.py

Change-Id: I639cf673a983b7b1be810495d8a8c2d89919a9b6
(cherry picked from commit 178227c8b6636433fcdab4dfd342468335b76aa6)
(cherry picked from commit c874c44cdc0dc32ae1bdcedfce4a2a9319d8e1eb)
---
 neutron/agent/ovsdb/impl_idl.py         |  4 +++-
 neutron/common/utils.py                 | 12 ++++++++++++
 neutron/tests/unit/common/test_utils.py | 18 ++++++++++++++++++
 3 files changed, 33 insertions(+), 1 deletion(-)

diff --git a/neutron/agent/ovsdb/impl_idl.py b/neutron/agent/ovsdb/impl_idl.py
index 603102583d1..25256687859 100644
--- a/neutron/agent/ovsdb/impl_idl.py
+++ b/neutron/agent/ovsdb/impl_idl.py
@@ -22,6 +22,7 @@ from ovsdbapp.backend.ovs_idl import vlog
 from ovsdbapp.schema.open_vswitch import impl_idl
 
 from neutron.agent.ovsdb.native import connection as n_connection
+from neutron.common import utils
 from neutron.conf.agent import ovs_conf
 from neutron.plugins.ml2.drivers.openvswitch.agent.common import constants
 
@@ -83,12 +84,13 @@ class OvsCleanup(command.BaseCommand):
         return True
 
 
+@utils.SingletonDecorator
 class NeutronOvsdbIdl(impl_idl.OvsdbIdl):
     def __init__(self, connection, idl_monitor):
         max_level = None if cfg.CONF.OVS.ovsdb_debug else vlog.INFO
         vlog.use_python_logger(max_level=max_level)
         self.idl_monitor = idl_monitor
-        super(NeutronOvsdbIdl, self).__init__(connection)
+        impl_idl.OvsdbIdl.__init__(self, connection)
 
     def ovs_cleanup(self, bridges, all_ports=False):
         return OvsCleanup(self, bridges, all_ports)
diff --git a/neutron/common/utils.py b/neutron/common/utils.py
index cc2685b4785..bff10bc40a2 100644
--- a/neutron/common/utils.py
+++ b/neutron/common/utils.py
@@ -982,3 +982,15 @@ def timecost(f):
         ret = f(*args, **kwargs)
         return ret
     return wrapper
+
+
+class SingletonDecorator(object):
+
+    def __init__(self, klass):
+        self._klass = klass
+        self._instance = None
+
+    def __call__(self, *args, **kwargs):
+        if self._instance is None:
+            self._instance = self._klass(*args, **kwargs)
+        return self._instance
diff --git a/neutron/tests/unit/common/test_utils.py b/neutron/tests/unit/common/test_utils.py
index 80461253980..be373964d05 100644
--- a/neutron/tests/unit/common/test_utils.py
+++ b/neutron/tests/unit/common/test_utils.py
@@ -624,3 +624,21 @@ class SpawnWithOrWithoutProfilerTestCase(
 
     def test_spawn_without_profiler(self):
         self._compare_profilers_in_parent_and_in_child(init_profiler=False)
+
+
+@utils.SingletonDecorator
+class _TestSingletonClass(object):
+
+    def __init__(self):
+        self.variable = None
+
+
+class SingletonDecoratorTestCase(base.BaseTestCase):
+
+    def test_singleton_instance_class(self):
+        instance_1 = _TestSingletonClass()
+        instance_1.variable = 'value1'
+
+        instance_2 = _TestSingletonClass()
+        self.assertEqual(instance_1.__hash__(), instance_2.__hash__())
+        self.assertEqual('value1', instance_2.variable)