Extend decision engine to support threading mode

With the events of eventlet removal, Watcher will need
to be adapted to support both modes, eventlet and threading, for
a couple of releases before removing all eventlet code.
This patch adds methods and classes that allow decision engine
modules to create futurist thread pools instead of green thread pools,
based on a environment variable that can be enabled by service.
It moves continuous audit handler instance to decison engine service,
so it can be started together with the main decision engine service.
Adds an environment variable that allows the user to disable
eventlet monkey patching and to use oslo.service threading backend.

Change-Id: I8a8be0a7cebdc44005fd77ec960543828c7da318
Signed-off-by: Douglas Viroel <viroel@gmail.com>

watcher/decision_engine/messaging/audit_endpoint.py

@@ -16,12 +16,10 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 #
-import futurist
-
 from oslo_config import cfg
 from oslo_log import log
 
-from watcher.decision_engine.audit import continuous as c_handler
+from watcher.common import executor
 from watcher.decision_engine.audit import event as e_handler
 from watcher.decision_engine.audit import oneshot as o_handler
 
@@ -35,10 +33,10 @@ class AuditEndpoint(object):
 
     def __init__(self, messaging):
         self._messaging = messaging
-        self._executor = futurist.GreenThreadPoolExecutor(
-            max_workers=CONF.watcher_decision_engine.max_audit_workers)
+        self.amount_workers = CONF.watcher_decision_engine.max_audit_workers
+        self._executor = (
+            executor.get_futurist_pool_executor(self.amount_workers))
         self._oneshot_handler = o_handler.OneShotAuditHandler()
-        self._continuous_handler = c_handler.ContinuousAuditHandler().start()
         self._event_handler = e_handler.EventAuditHandler()
 
     @property

watcher/decision_engine/service.py

@@ -13,6 +13,7 @@
 # under the License.
 
 from watcher.common import service as watcher_service
+from watcher.decision_engine.audit import continuous as c_handler
 from watcher.decision_engine import manager
 from watcher.decision_engine import scheduling
 
@@ -31,6 +32,7 @@ class DecisionEngineService(watcher_service.Service):
         # task, an one shot task to cancel ongoing audits and a periodic
         # check for expired action plans
         self._bg_scheduler = None
+        self._continuous_handler = None
 
     @property
     def bg_scheduler(self):
@@ -38,10 +40,17 @@ class DecisionEngineService(watcher_service.Service):
             self._bg_scheduler = scheduling.DecisionEngineSchedulingService()
         return self._bg_scheduler
 
+    @property
+    def continuous_handler(self):
+        if self._continuous_handler is None:
+            self._continuous_handler = c_handler.ContinuousAuditHandler()
+        return self._continuous_handler
+
     def start(self):
         """Start service."""
         super().start()
         self.bg_scheduler.start()
+        self.continuous_handler.start()
 
     def stop(self):
         """Stop service."""

watcher/decision_engine/threading.py

@@ -17,13 +17,14 @@
 # limitations under the License.
 
 import copy
-import futurist
 from futurist import waiters
 
 from oslo_config import cfg
 from oslo_log import log
 from oslo_service import service
 
+from watcher.common import executor
+
 CONF = cfg.CONF
 LOG = log.getLogger(__name__)
 
@@ -33,8 +34,8 @@ class DecisionEngineThreadPool(object, metaclass=service.Singleton):
 
     def __init__(self):
         self.amount_workers = CONF.watcher_decision_engine.max_general_workers
-        self._threadpool = futurist.GreenThreadPoolExecutor(
-            max_workers=self.amount_workers)
+        self._threadpool = (
+            executor.get_futurist_pool_executor(self.amount_workers))
 
     def submit(self, fn, *args, **kwargs):
         """Will submit the job to the underlying threadpool