Refactor periodic tasks.

This review allows periodic tasks to be enabled or disabled in the
decorator, as well as by specifying an interval which is negative.

The spacing between runs of a periodic task is now specified in
seconds, with zero meaning the default spacing which is currently 60
seconds.

There is also a new argument to the decorator which indicates if a
periodic task _needs_ to be run in the nova-compute process. There is
also a flag (run_external_periodic_tasks) which can be used to move
these periodic tasks out of the nova-compute process.

I also remove the periodic_interval flag to services, as the interval
between runs is now dynamic based on the number of seconds that a
periodic task wants to wait for its next run. For callers who want to
twiddle the sleep period (for example unit tests), there is a
create() argument periodic_interval_max which lets the period
periodic_tasks() specifies be overridden. This is not exposed as a
flag because I cannot see a use case for that. It is needed for unit
testing however.

DocImpact. Resolves bug 939087.

Change-Id: I7f245a88b8d229a481c1b65a4c0f1e2769bf3901

1 files changed, 21 insertions, 17 deletions

diff --git a/nova/service.py b/nova/service.py
index 4c93fefa8..fc0ac4a1b 100644
--- a/nova/service.py
+++ b/nova/service.py
@@ -49,9 +49,9 @@ service_opts = [
     cfg.IntOpt('report_interval',
                default=10,
                help='seconds between nodes reporting state to datastore'),
-    cfg.IntOpt('periodic_interval',
-               default=60,
-               help='seconds between running periodic tasks'),
+    cfg.BoolOpt('periodic_enable',
+               default=True,
+               help='enable periodic tasks'),
     cfg.IntOpt('periodic_fuzzy_delay',
                default=60,
                help='range of seconds to randomly delay when starting the'
@@ -371,7 +371,8 @@ class Service(object):
     it state to the database services table."""
 
     def __init__(self, host, binary, topic, manager, report_interval=None,
-                 periodic_interval=None, periodic_fuzzy_delay=None,
+                 periodic_enable=None, periodic_fuzzy_delay=None,
+                 periodic_interval_max=None,
                  *args, **kwargs):
         self.host = host
         self.binary = binary
@@ -380,8 +381,9 @@ class Service(object):
         manager_class = importutils.import_class(self.manager_class_name)
         self.manager = manager_class(host=self.host, *args, **kwargs)
         self.report_interval = report_interval
-        self.periodic_interval = periodic_interval
+        self.periodic_enable = periodic_enable
         self.periodic_fuzzy_delay = periodic_fuzzy_delay
+        self.periodic_interval_max = periodic_interval_max
         self.saved_args, self.saved_kwargs = args, kwargs
         self.timers = []
         self.backdoor_port = None
@@ -433,15 +435,15 @@ class Service(object):
         if pulse:
             self.timers.append(pulse)
 
-        if self.periodic_interval:
+        if self.periodic_enable:
             if self.periodic_fuzzy_delay:
                 initial_delay = random.randint(0, self.periodic_fuzzy_delay)
             else:
                 initial_delay = None
 
-            periodic = utils.LoopingCall(self.periodic_tasks)
-            periodic.start(interval=self.periodic_interval,
-                           initial_delay=initial_delay)
+            periodic = utils.DynamicLoopingCall(self.periodic_tasks)
+            periodic.start(initial_delay=initial_delay,
+                           periodic_interval_max=self.periodic_interval_max)
             self.timers.append(periodic)
 
     def _create_service_ref(self, context):
@@ -460,8 +462,8 @@ class Service(object):
 
     @classmethod
     def create(cls, host=None, binary=None, topic=None, manager=None,
-               report_interval=None, periodic_interval=None,
-               periodic_fuzzy_delay=None):
+               report_interval=None, periodic_enable=None,
+               periodic_fuzzy_delay=None, periodic_interval_max=None):
         """Instantiates class and passes back application object.
 
         :param host: defaults to CONF.host
@@ -469,8 +471,9 @@ class Service(object):
         :param topic: defaults to bin_name - 'nova-' part
         :param manager: defaults to CONF.<topic>_manager
         :param report_interval: defaults to CONF.report_interval
-        :param periodic_interval: defaults to CONF.periodic_interval
+        :param periodic_enable: defaults to CONF.periodic_enable
         :param periodic_fuzzy_delay: defaults to CONF.periodic_fuzzy_delay
+        :param periodic_interval_max: if set, the max time to wait between runs
 
         """
         if not host:
@@ -486,14 +489,15 @@ class Service(object):
             manager = CONF.get(manager_cls, None)
         if report_interval is None:
             report_interval = CONF.report_interval
-        if periodic_interval is None:
-            periodic_interval = CONF.periodic_interval
+        if periodic_enable is None:
+            periodic_enable = CONF.periodic_enable
         if periodic_fuzzy_delay is None:
             periodic_fuzzy_delay = CONF.periodic_fuzzy_delay
         service_obj = cls(host, binary, topic, manager,
                           report_interval=report_interval,
-                          periodic_interval=periodic_interval,
-                          periodic_fuzzy_delay=periodic_fuzzy_delay)
+                          periodic_enable=periodic_enable,
+                          periodic_fuzzy_delay=periodic_fuzzy_delay,
+                          periodic_interval_max=periodic_interval_max)
 
         return service_obj
 
@@ -529,7 +533,7 @@ class Service(object):
     def periodic_tasks(self, raise_on_error=False):
         """Tasks to be run at a periodic interval."""
         ctxt = context.get_admin_context()
-        self.manager.periodic_tasks(ctxt, raise_on_error=raise_on_error)
+        return self.manager.periodic_tasks(ctxt, raise_on_error=raise_on_error)
 
 
 class WSGIService(object):