Add Timer to rally.utils

This is small and pretty class for with statement that measure time.

Example of usage:

with Timer() as timer:
	#do some dirty stuff
time_in_seconds = timer.duration()

It will be used at least by our Test engine.

Change-Id: I3bf0075df807c2118d5872dd425aae0061232133

rally/utils.py

@@ -20,6 +20,7 @@ import os
 import StringIO
 import sys
 import time
+import traceback
 
 from rally import exceptions
 from rally.openstack.common.gettextutils import _   # noqa
@@ -69,6 +70,22 @@ class StdErrCapture(object):
         sys.stderr = self.stderr
 
 
+class Timer(object):
+    def __enter__(self):
+        self.error = None
+        self.start = time.time()
+        return self
+
+    def __exit__(self, type, value, tb):
+        self.finish = time.time()
+        if type:
+            tb = traceback.print_exception(type, value, tb)
+            self.error = (type, value, tb)
+
+    def duration(self):
+        return self.finish - self.start
+
+
 def itersubclasses(cls, _seen=None):
     """Generator over all subclasses of a given class in depth first order."""
 

tests/test_utils.py

@@ -20,7 +20,9 @@
 from __future__ import print_function
 
 import datetime
+import mock
 import sys
+import time
 
 from rally import exceptions
 from rally import test
@@ -82,6 +84,30 @@ class StdIOCaptureTestCase(test.NoDBTestCase):
         self.assertEqual(stderr, sys.stderr)
 
 
+class TimerTestCase(test.NoDBTestCase):
+
+    def test_timer_duration(self):
+        start_time = time.time()
+        end_time = time.time()
+
+        with mock.patch('rally.utils.time') as mock_time:
+            mock_time.time = mock.MagicMock(return_value=start_time)
+            with utils.Timer() as timer:
+                mock_time.time = mock.MagicMock(return_value=end_time)
+
+        self.assertIsNone(timer.error)
+        self.assertEqual(end_time - start_time, timer.duration())
+
+    def test_timer_exception(self):
+        try:
+            with utils.Timer() as timer:
+                raise Exception()
+        except Exception:
+            pass
+        self.assertEqual(3, len(timer.error))
+        self.assertEqual(timer.error[0], type(Exception()))
+
+
 class IterSubclassesTestCase(test.NoDBTestCase):
 
     def test_itersubclasses(self):