From: Tom Cammann <tom.cammann@hp.com>
Date: Fri, 4 Jul 2014 08:22:46 +0000 (+0100)
Subject: sync periodic_task fix from incubator
X-Git-Url: https://review.fuel-infra.org/gitweb?a=commitdiff_plain;h=51e0b5b5152b9e85a4297308ecc3b653e29e8c18;p=openstack-build%2Fcinder-build.git

sync periodic_task fix from incubator

Set the value of time the periodic task was last run to a multiple of
the spacing value rather than the actual last time run. This ensures
tasks runs regularly but avoids synchronizing that interval with other
nodes.

This patch also removes the coalescing of tasks which are _nearby_ (0.2
seconds away).

Changes:

periodic_task
-------------
4dbd3aa Make periodic tasks run on regular spacing interval
21249f1 Fix parenthesis typo misunderstanding in periodic_task

Change-Id: I6c06ae73b18d4425a987a215a050bc70335e490e
---

diff --git a/cinder/openstack/common/periodic_task.py b/cinder/openstack/common/periodic_task.py
index e5d32e39c..c4a2bd37f 100644
--- a/cinder/openstack/common/periodic_task.py
+++ b/cinder/openstack/common/periodic_task.py
@@ -11,6 +11,7 @@
 #    License for the specific language governing permissions and limitations
 #    under the License.
 
+import random
 import time
 
 from oslo.config import cfg
@@ -80,14 +81,14 @@ def periodic_task(*args, **kwargs):
         return f
 
     # NOTE(sirp): The `if` is necessary to allow the decorator to be used with
-    # and without parents.
+    # and without parenthesis.
     #
-    # In the 'with-parents' case (with kwargs present), this function needs to
-    # return a decorator function since the interpreter will invoke it like:
+    # In the 'with-parenthesis' case (with kwargs present), this function needs
+    # to return a decorator function since the interpreter will invoke it like:
     #
     #   periodic_task(*args, **kwargs)(f)
     #
-    # In the 'without-parents' case, the original function will be passed
+    # In the 'without-parenthesis' case, the original function will be passed
     # in as the first argument, like:
     #
     #   periodic_task(f)
@@ -142,6 +143,27 @@ class _PeriodicTasksMeta(type):
                 cls._periodic_spacing[name] = task._periodic_spacing
 
 
+def _nearest_boundary(last_run, spacing):
+    """Find nearest boundary which is in the past, which is a multiple of the
+    spacing with the last run as an offset.
+
+    Eg if last run was 10 and spacing was 7, the new last run could be: 17, 24,
+    31, 38...
+
+    0% to 5% of the spacing value will be added to this value to ensure tasks
+    do not synchronize. This jitter is rounded to the nearest second, this
+    means that spacings smaller than 20 seconds will not have jitter.
+    """
+    current_time = time.time()
+    if last_run is None:
+        return current_time
+    delta = current_time - last_run
+    offset = delta % spacing
+    # Add up to 5% jitter
+    jitter = int(spacing * (random.random() / 20))
+    return current_time - offset + jitter
+
+
 @six.add_metaclass(_PeriodicTasksMeta)
 class PeriodicTasks(object):
     def __init__(self):
@@ -159,17 +181,18 @@ class PeriodicTasks(object):
             spacing = self._periodic_spacing[task_name]
             last_run = self._periodic_last_run[task_name]
 
-            # If a periodic task is _nearly_ due, then we'll run it early
+            # Check if due, if not skip
             idle_for = min(idle_for, spacing)
             if last_run is not None:
                 delta = last_run + spacing - time.time()
-                if delta > 0.2:
+                if delta > 0:
                     idle_for = min(idle_for, delta)
                     continue
 
             LOG.debug("Running periodic task %(full_task_name)s",
                       {"full_task_name": full_task_name})
-            self._periodic_last_run[task_name] = time.time()
+            self._periodic_last_run[task_name] = _nearest_boundary(
+                last_run, spacing)
 
             try:
                 task(self, context)