Add pause function to executor

The pause function in the executor would facilitate rolling updates in
environments like OpenShift that normally restart services. By
utilizing the governor sensor mechanism it is now easy to add the
pause function.

Change-Id: I2c1f48392514ae9e72f2587a88ef66200cbfdcf8

tests/unit/test_executor.py

@@ -464,6 +464,14 @@ class TestGovernor(ZuulTestCase):
         self.executor_server.manageLoad()
         self.assertFalse(self.executor_server.accepting_work)
 
+    def test_pause_governor(self):
+        self.executor_server.manageLoad()
+        self.assertTrue(self.executor_server.accepting_work)
+
+        self.executor_server.pause_sensor.pause = True
+        self.executor_server.manageLoad()
+        self.assertFalse(self.executor_server.accepting_work)
+
     def waitForExecutorBuild(self, jobname):
         self.log.debug("Waiting for %s to start", jobname)
         timeout = time.time() + 30

zuul/executor/sensors/pause.py

@@ -0,0 +1,37 @@
+# Copyright 2018 BMW Car IT GmbH
+#
+# Licensed under the Apache License, Version 2.0 (the "License"); you may
+# not use this file except in compliance with the License. You may obtain
+# a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+# WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+# License for the specific language governing permissions and limitations
+# under the License.
+
+import logging
+
+from zuul.executor.sensors import SensorInterface
+
+
+class PauseSensor(SensorInterface):
+    log = logging.getLogger("zuul.executor.sensor.pause")
+
+    def __init__(self):
+        self.pause = False
+
+    def isOk(self):
+        if self.pause:
+            return False, 'paused'
+        else:
+            return True, 'running'
+
+    def reportStats(self, statsd, base_key):
+        if self.pause:
+            value = 1
+        else:
+            value = 0
+        statsd.gauge(base_key + '.pause', value)

zuul/executor/server.py

@@ -26,6 +26,7 @@ import tempfile
 import threading
 import time
 import traceback
+
 from zuul.lib.yamlutil import yaml
 from zuul.lib.config import get_default
 from zuul.lib.statsd import get_statsd
@@ -39,6 +40,7 @@ import gear
 import zuul.merger.merger
 import zuul.ansible.logconfig
 from zuul.executor.sensors.cpu import CPUSensor
+from zuul.executor.sensors.pause import PauseSensor
 from zuul.executor.sensors.startingbuilds import StartingBuildsSensor
 from zuul.executor.sensors.ram import RAMSensor
 from zuul.lib import commandsocket
@@ -1868,9 +1870,11 @@ class ExecutorServer(object):
                                               self.stopJobDiskFull,
                                               self.merge_root)
 
+        self.pause_sensor = PauseSensor()
         cpu_sensor = CPUSensor(config)
         self.sensors = [
             cpu_sensor,
+            self.pause_sensor,
             RAMSensor(config),
             StartingBuildsSensor(self, cpu_sensor.max_load_avg)
         ]
@@ -2005,12 +2009,10 @@ class ExecutorServer(object):
         self.executor_thread.join()
 
     def pause(self):
-        # TODOv3: implement
-        pass
+        self.pause_sensor.pause = True
 
     def unpause(self):
-        # TODOv3: implement
-        pass
+        self.pause_sensor.pause = False
 
     def graceful(self):
         # TODOv3: implement