Fix concurrency issue with snmp pollsters

pysnmp oneliner.CommandGenerator() is not thread safe.

This change creates one oneliner.CommandGenerator() per query to fix
the issue.

Closes-bug: #1576577

Change-Id: Ibf32c068abed5d7198150bc206987f050a093cd8
(cherry picked from commit c898ecd921123eab61a8f88e61686ab4edf82b35)

2 files changed, 19 insertions, 30 deletions

diff --git a/ceilometer/hardware/inspector/snmp.py b/ceilometer/hardware/inspector/snmp.py
index a9d937be..0ea1d27e 100644
--- a/ceilometer/hardware/inspector/snmp.py
+++ b/ceilometer/hardware/inspector/snmp.py
@@ -128,10 +128,6 @@ class SNMPInspector(base.Inspector):
          extra.update('project_id': xy, 'user_id': zw)
     """
 
-    def __init__(self):
-        super(SNMPInspector, self).__init__()
-        self._cmdGen = cmdgen.CommandGenerator()
-
     def _query_oids(self, host, oids, cache, is_bulk):
         # send GetRequest or GetBulkRequest to get oid values and
         # populate the values into cache
@@ -140,17 +136,13 @@ class SNMPInspector(base.Inspector):
                                                host.port or self._port))
         oid_cache = cache.setdefault(self._CACHE_KEY_OID, {})
 
+        cmd_runner = cmdgen.CommandGenerator()
         if is_bulk:
-            ret = self._cmdGen.bulkCmd(authData,
-                                       transport,
-                                       0, 100,
-                                       *oids,
-                                       lookupValues=True)
+            ret = cmd_runner.bulkCmd(authData, transport, 0, 100, *oids,
+                                     lookupValues=True)
         else:
-            ret = self._cmdGen.getCmd(authData,
-                                      transport,
-                                      *oids,
-                                      lookupValues=True)
+            ret = cmd_runner.getCmd(authData, transport, *oids,
+                                    lookupValues=True)
         (error, data) = parse_snmp_return(ret, is_bulk)
         if error:
             raise SNMPException("An error occurred, oids %(oid)s, "
diff --git a/ceilometer/tests/unit/hardware/inspector/test_snmp.py b/ceilometer/tests/unit/hardware/inspector/test_snmp.py
index b7286232..8899ad6d 100644
--- a/ceilometer/tests/unit/hardware/inspector/test_snmp.py
+++ b/ceilometer/tests/unit/hardware/inspector/test_snmp.py
@@ -33,19 +33,19 @@ class FakeObjectName(object):
         return str(self.name)
 
 
-def faux_getCmd_new(authData, transportTarget, *oids, **kwargs):
-    varBinds = [(FakeObjectName(oid),
-                 int(oid.split('.')[-1])) for oid in oids]
-    return (None, None, 0, varBinds)
+class FakeCommandGenerator(object):
+    def getCmd(self, authData, transportTarget, *oids, **kwargs):
+        varBinds = [(FakeObjectName(oid),
+                    int(oid.split('.')[-1])) for oid in oids]
+        return (None, None, 0, varBinds)
 
-
-def faux_bulkCmd_new(authData, transportTarget, nonRepeaters, maxRepetitions,
-                     *oids, **kwargs):
-    varBindTable = [
-        [(FakeObjectName(oid + ".%d" % i), i) for i in range(1, 3)]
-        for oid in oids
-    ]
-    return (None, None, 0, varBindTable)
+    def bulkCmd(authData, transportTarget, nonRepeaters, maxRepetitions,
+                *oids, **kwargs):
+        varBindTable = [
+            [(FakeObjectName("%s.%d" % (oid, i)), i) for i in range(1, 3)]
+            for oid in oids
+        ]
+        return (None, None, 0, varBindTable)
 
 
 class TestSNMPInspector(test_base.BaseTestCase):
@@ -73,9 +73,8 @@ class TestSNMPInspector(test_base.BaseTestCase):
         self.inspector = snmp.SNMPInspector()
         self.host = netutils.urlsplit("snmp://localhost")
         self.useFixture(mockpatch.PatchObject(
-            self.inspector._cmdGen, 'getCmd', new=faux_getCmd_new))
-        self.useFixture(mockpatch.PatchObject(
-            self.inspector._cmdGen, 'bulkCmd', new=faux_bulkCmd_new))
+            snmp.cmdgen, 'CommandGenerator',
+            return_value=FakeCommandGenerator()))
 
     def test_snmp_error(self):
         def get_list(func, *args, **kwargs):
@@ -133,8 +132,6 @@ class TestSNMPInspector(test_base.BaseTestCase):
         self.assertEqual(ret[0][0], ret[0][1]['meta'])
 
     def test_post_op_net(self):
-        self.useFixture(mockpatch.PatchObject(
-            self.inspector._cmdGen, 'bulkCmd', new=faux_bulkCmd_new))
         cache = {}
         metadata = dict(name='lo',
                         speed=0,