Call pre/post run task calls from TaskManager.submit_task()

Since I33325fb5be21264df0a68ceef2202ab7875f63ec, the task.run() call
in TaskManager.run_task() is now an asynchronous submission to the
threadpool, rather than a synchronous call to the task's actual
function.  This means taking the elapsed_time around this call is no
longer an indication of the task's runtime, but always comes out as
just a few μs for the insertion.

Move the pre and post calls into TaskManager.submit_task() where the
elapsed_time will reflect the time between insertion into the queue
and the wait() return of its result.

Update documentation for pre/post tasks, and add test-cases.

Depends-On: https://review.openstack.org/613438
Change-Id: I8617ab2895d1544a6902ae5a3d6a97b87bfd2ec9

openstack/task_manager.py

@@ -167,8 +167,14 @@ class TaskManager(object):
             raise exceptions.TaskManagerStopped(
                 "TaskManager {name} is no longer running".format(
                     name=self.name))
+        self.pre_run_task(task)
+        start = time.time()
         self.queue.put(task)
-        return task.wait()
+        ret = task.wait()
+        end = time.time()
+        dt = end - start
+        self.post_run_task(dt, task)
+        return ret
 
     def submit_function(
             self, method, name=None, run_async=False, *args, **kwargs):
@@ -204,6 +210,13 @@ class TaskManager(object):
             method, name=name, run_async=True, *args, **kwargs)
 
     def pre_run_task(self, task):
+        '''Callback when task enters the task queue
+
+        :param task: the task
+
+        Intended to be overridden by child classes to track task
+        progress.
+        '''
         self._log.debug(
             "Manager %s running task %s", self.name, task.name)
 
@@ -213,14 +226,21 @@ class TaskManager(object):
         # code is designed so that caller of submit_task (which may be
         # in a different thread than this run_task) gets the
         # exception.
-        self.pre_run_task(task)
-        start = time.time()
+        #
+        # Note all threads go through the threadpool, so this is an
+        # async call.  submit_task will wait() for the final result.
         task.run()
-        end = time.time()
-        dt = end - start
-        self.post_run_task(dt, task)
 
     def post_run_task(self, elapsed_time, task):
+        '''Callback at task completion
+
+        :param float elapsed_time: time in seconds between task entering
+            queue and finishing
+        :param task: the task
+
+        This function is intended to be overridden by child classes to
+        monitor task runtimes.
+        '''
         self._log.debug(
             "Manager %s ran task %s in %ss",
             self.name, task.name, elapsed_time)

openstack/tests/unit/cloud/test_task_manager.py

@@ -17,6 +17,7 @@ import concurrent.futures
 import fixtures
 import mock
 import threading
+import time
 
 from six.moves import queue
 
@@ -105,6 +106,28 @@ class TestTaskManager(base.TestCase):
         self.manager.submit_function(set, run_async=True)
         self.assertTrue(mock_submit.called)
 
+    @mock.patch.object(task_manager.TaskManager, 'post_run_task')
+    @mock.patch.object(task_manager.TaskManager, 'pre_run_task')
+    def test_pre_post_calls(self, mock_pre, mock_post):
+        self.manager.submit_function(lambda: None)
+        mock_pre.assert_called_once()
+        mock_post.assert_called_once()
+
+    @mock.patch.object(task_manager.TaskManager, 'post_run_task')
+    @mock.patch.object(task_manager.TaskManager, 'pre_run_task')
+    def test_validate_timing(self, mock_pre, mock_post):
+        # Note the unit test setup has mocked out time.sleep() and
+        # done a * 0.0001, and the test should be under the 5
+        # second timeout.  Thus with below, we should see at
+        # *least* a 1 second pause running the task.
+        self.manager.submit_function(lambda: time.sleep(10000))
+
+        mock_pre.assert_called_once()
+        mock_post.assert_called_once()
+
+        args, kwargs = mock_post.call_args_list[0]
+        self.assertTrue(args[0] > 1.0)
+
 
 class ThreadingTaskManager(task_manager.TaskManager):
     """A subclass of TaskManager which exercises the thread-shifting

releasenotes/notes/fix-task-timing-048afea680adc62e.yaml

@@ -0,0 +1,5 @@
+---
+fixes:
+  - |
+    Fix a regression where the ``TaskManager.post_run_task`` ``elapsed_time``
+    argument was not reflecting the time taken by the actual task.