Add basic periodic task infrastructure.

So the idea is Manager will inherit from PeriodTasks
and create a timer to call run_periodic_tasks().

Part of blueprint service-infrastructure

Signed-off-by: Angus Salkeld <asalkeld@redhat.com>
Change-Id: I822b8501ad184d0e5885cada1a3d7a847e2ca12c

1 files changed, 112 insertions, 0 deletions

diff --git a/openstack/common/periodic_task.py b/openstack/common/periodic_task.py
new file mode 100644
index 0000000..5cf2ade
--- /dev/null
+++ b/openstack/common/periodic_task.py
@@ -0,0 +1,112 @@
+# vim: tabstop=4 shiftwidth=4 softtabstop=4
+
+#
+#    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.
+
+from openstack.common import log as logging
+from openstack.common.gettextutils import _
+
+LOG = logging.getLogger(__name__)
+
+
+def periodic_task(*args, **kwargs):
+    """Decorator to indicate that a method is a periodic task.
+
+    This decorator can be used in two ways:
+
+        1. Without arguments '@periodic_task', this will be run on every tick
+           of the periodic scheduler.
+
+        2. With arguments, @periodic_task(ticks_between_runs=N), this will be
+           run on every N ticks of the periodic scheduler.
+    """
+    def decorator(f):
+        f._periodic_task = True
+        f._ticks_between_runs = kwargs.pop('ticks_between_runs', 0)
+        return f
+
+    # NOTE(sirp): The `if` is necessary to allow the decorator to be used with
+    # and without parens.
+    #
+    # In the 'with-parens' 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-parens' case, the original function will be passed
+    # in as the first argument, like:
+    #
+    #   periodic_task(f)
+    if kwargs:
+        return decorator
+    else:
+        return decorator(args[0])
+
+
+class _PeriodicTasksMeta(type):
+    def __init__(cls, names, bases, dict_):
+        """Metaclass that allows us to collect decorated periodic tasks."""
+        super(_PeriodicTasksMeta, cls).__init__(names, bases, dict_)
+
+        # NOTE(sirp): if the attribute is not present then we must be the base
+        # class, so, go ahead and initialize it. If the attribute is present,
+        # then we're a subclass so make a copy of it so we don't step on our
+        # parent's toes.
+        try:
+            cls._periodic_tasks = cls._periodic_tasks[:]
+        except AttributeError:
+            cls._periodic_tasks = []
+
+        try:
+            cls._ticks_to_skip = cls._ticks_to_skip.copy()
+        except AttributeError:
+            cls._ticks_to_skip = {}
+
+        # This uses __dict__ instead of
+        # inspect.getmembers(cls, inspect.ismethod) so only the methods of the
+        # current class are added when this class is scanned, and base classes
+        # are not added redundantly.
+        for value in cls.__dict__.values():
+            if getattr(value, '_periodic_task', False):
+                task = value
+                name = task.__name__
+                cls._periodic_tasks.append((name, task))
+                cls._ticks_to_skip[name] = task._ticks_between_runs
+
+
+class PeriodicTasks(object):
+    __metaclass__ = _PeriodicTasksMeta
+
+    def run_periodic_tasks(self, *args, **kwargs):
+        """Tasks to be run at a periodic interval."""
+        raise_on_error = kwargs.get('raise_on_error', False)
+        for task_name, task in self._periodic_tasks:
+            full_task_name = '.'.join([self.__class__.__name__, task_name])
+
+            ticks_to_skip = self._ticks_to_skip[task_name]
+            if ticks_to_skip > 0:
+                LOG.debug(_("Skipping %(full_task_name)s, %(ticks_to_skip)s"
+                            " ticks left until next run"), locals())
+                self._ticks_to_skip[task_name] -= 1
+                continue
+
+            self._ticks_to_skip[task_name] = task._ticks_between_runs
+            LOG.debug(_("Running periodic task %(full_task_name)s"), locals())
+
+            try:
+                task(self, *args, **kwargs)
+            except Exception as e:
+                if raise_on_error:
+                    raise
+                LOG.exception(_("Error during %(full_task_name)s: %(e)s"),
+                              locals())