tests: Reduce likelihood of auth_log test locking up during CI

We would sometimes see the auth_log test hang during a CI run. The CI
job would eventually fail after consuming a costly 10 hours of CI
runtime.

We believe the problem is around the test creating multiple instances of
the Messaging() context. This is a similar race condition to what was
seen in 19f34b2161.

Currently a new Messaging() context is created for every test case. By
using classmethods instead, the Messaging context is only created once
per python test file execution (i.e. creation of the python class,
rather than initialization of the python object, which happens for every
test-case).

This means the test will only create one Messaging() context, which
should avoid any race conditions.

Changes:
+ removed msg_ctxs - this wasn't actually used for anything.
+ use classmethods to setup and tear-down the Messaging() context (and
tweak lp initialization accordingly).
+ fix discardMessages() - the loop wasn't actually discarding any
messages previously (this may also have been the cause of the test
hanging).

Signed-off-by: Aaron Haslett <aaronhaslett@catalyst.net.nz>
Signed-off-by: Tim Beale <timbeale@catalyst.net.nz>
Reviewed-by: Noel Power <npower@samba.org>

Autobuild-User(master): Noel Power <npower@samba.org>
Autobuild-Date(master): Tue Mar  5 13:10:43 UTC 2019 on sn-devel-144

python/samba/tests/auth_log_base.py

@@ -27,14 +27,13 @@ import time
 import json
 import os
 import re
-
-msg_ctxs = []
+from samba import param
 
 
 class AuthLogTestBase(samba.tests.TestCase):
 
-    def setUp(self):
-        super(AuthLogTestBase, self).setUp()
+    @classmethod
+    def setUpClass(self):
         # connect to the server's messaging bus (we need to explicitly load a
         # different smb.conf here, because in all other respects this test
         # wants to act as a separate remote client)
@@ -42,16 +41,14 @@ class AuthLogTestBase(samba.tests.TestCase):
         if server_conf:
             lp_ctx = LoadParm(filename_for_non_global_lp=server_conf)
         else:
-            lp_ctx = self.get_loadparm()
+            samba.tests.env_loadparm()
         self.msg_ctx = Messaging((1,), lp_ctx=lp_ctx)
-        global msg_ctxs
-        msg_ctxs.append(self.msg_ctx)
         self.msg_ctx.irpc_add_name(AUTH_EVENT_NAME)
 
         # Now switch back to using the client-side smb.conf. The tests will
         # use the first interface in the client.conf (we need to strip off
         # the subnet mask portion)
-        lp_ctx = self.get_loadparm()
+        lp_ctx = samba.tests.env_loadparm()
         client_ip_and_mask = lp_ctx.get('interfaces')[0]
         client_ip = client_ip_and_mask.split('/')[0]
 
@@ -71,18 +68,21 @@ class AuthLogTestBase(samba.tests.TestCase):
         self.msg_ctx.register(self.msg_handler_and_context,
                               msg_type=MSG_AUTH_LOG)
 
-        self.discardMessages()
-
         self.remoteAddress = None
         self.server = os.environ["SERVER"]
         self.connection = None
 
-    def tearDown(self):
+    @classmethod
+    def tearDownClass(self):
         if self.msg_handler_and_context:
             self.msg_ctx.deregister(self.msg_handler_and_context,
                                     msg_type=MSG_AUTH_LOG)
             self.msg_ctx.irpc_remove_name(AUTH_EVENT_NAME)
 
+    def setUp(self):
+        super(AuthLogTestBase, self).setUp()
+        self.discardMessages()
+
     def waitForMessages(self, isLastExpectedMessage, connection=None):
         """Wait for all the expected messages to arrive
         The connection is passed through to keep the connection alive
@@ -126,11 +126,12 @@ class AuthLogTestBase(samba.tests.TestCase):
         return list(filter(isRemote, self.context["messages"]))
 
     # Discard any previously queued messages.
+    @classmethod
     def discardMessages(self):
         self.msg_ctx.loop_once(0.001)
         while len(self.context["messages"]):
+            self.context["messages"] = []
             self.msg_ctx.loop_once(0.001)
-        self.context["messages"] = []
 
     # Remove any NETLOGON authentication messages
     # NETLOGON is only performed once per session, so to avoid ordering