text: #
  #    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.
  
  import copy
  import logging
  import random
  import time
  
  from oslo_config import cfg
  import six
  
  from senlin.openstack.common._i18n import _, _LE, _LI
  
  
  periodic_opts = [
      cfg.BoolOpt('run_external_periodic_tasks',
                  default=True,
                  help='Some periodic tasks can be run in a separate process. '
                       'Should we run them here?'),
  ]
  
  CONF = cfg.CONF
  CONF.register_opts(periodic_opts)
  
  LOG = logging.getLogger(__name__)
  
  DEFAULT_INTERVAL = 60.0
  
  
  def list_opts():
      """Entry point for oslo-config-generator."""
      return [(None, copy.deepcopy(periodic_opts))]
  
  
  class InvalidPeriodicTaskArg(Exception):
      message = _("Unexpected argument for periodic task creation: %(arg)s.")
  
  
  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 the default
             interval of 60 seconds.
  
          2. With arguments:
             @periodic_task(spacing=N [, run_immediately=[True|False]]
             [, name=[None|"string"])
             this will be run on approximately every N seconds. If this number is
             negative the periodic task will be disabled. If the run_immediately
             argument is provided and has a value of 'True', the first run of the
             task will be shortly after task scheduler starts.  If
             run_immediately is omitted or set to 'False', the first time the
             task runs will be approximately N seconds after the task scheduler
             starts. If name is not provided, __name__ of function is used.
      """
      def decorator(f):
          # Test for old style invocation
          if 'ticks_between_runs' in kwargs:
              raise InvalidPeriodicTaskArg(arg='ticks_between_runs')
  
          # Control if run at all
          f._periodic_task = True
          f._periodic_external_ok = kwargs.pop('external_process_ok', False)
          if f._periodic_external_ok and not CONF.run_external_periodic_tasks:
              f._periodic_enabled = False
          else:
              f._periodic_enabled = kwargs.pop('enabled', True)
          f._periodic_name = kwargs.pop('name', f.__name__)
  
          # Control frequency
          f._periodic_spacing = kwargs.pop('spacing', 0)
          f._periodic_immediate = kwargs.pop('run_immediately', False)
          if f._periodic_immediate:
              f._periodic_last_run = None
          else:
              f._periodic_last_run = time.time()
          return f
  
      # NOTE(sirp): The `if` is necessary to allow the decorator to be used with
      # and without parenthesis.
      #
      # 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-parenthesis' 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 _add_periodic_task(cls, task):
          """Add a periodic task to the list of periodic tasks.
  
          The task should already be decorated by @periodic_task.
  
          :return: whether task was actually enabled
          """
          name = task._periodic_name
  
          if task._periodic_spacing < 0:
              LOG.info(_LI('Skipping periodic task %(task)s because '
                           'its interval is negative'),
                       {'task': name})
              return False
          if not task._periodic_enabled:
              LOG.info(_LI('Skipping periodic task %(task)s because '
                           'it is disabled'),
                       {'task': name})
              return False
  
          # A periodic spacing of zero indicates that this task should
          # be run on the default interval to avoid running too
          # frequently.
          if task._periodic_spacing == 0:
              task._periodic_spacing = DEFAULT_INTERVAL
  
          cls._periodic_tasks.append((name, task))
          cls._periodic_spacing[name] = task._periodic_spacing
          return True
  
      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 an 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._periodic_spacing = cls._periodic_spacing.copy()
          except AttributeError:
              cls._periodic_spacing = {}
  
          for value in cls.__dict__.values():
              if getattr(value, '_periodic_task', False):
                  cls._add_periodic_task(value)
  
  
  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):
          super(PeriodicTasks, self).__init__()
          self._periodic_last_run = {}
          for name, task in self._periodic_tasks:
              self._periodic_last_run[name] = task._periodic_last_run
  
      def add_periodic_task(self, task):
          """Add a periodic task to the list of periodic tasks.
  
          The task should already be decorated by @periodic_task.
          """
          if self.__class__._add_periodic_task(task):
              self._periodic_last_run[task._periodic_name] = (
                  task._periodic_last_run)
  
      def run_periodic_tasks(self, context, raise_on_error=False):
          """Tasks to be run at a periodic interval."""
          idle_for = DEFAULT_INTERVAL
          for task_name, task in self._periodic_tasks:
              full_task_name = '.'.join([self.__class__.__name__, task_name])
  
              spacing = self._periodic_spacing[task_name]
              last_run = self._periodic_last_run[task_name]
  
              # 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:
                      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] = _nearest_boundary(
                  last_run, spacing)
  
              try:
                  task(self, context)
              except Exception as e:
                  if raise_on_error:
                      raise
                  LOG.exception(_LE("Error during %(full_task_name)s: %(e)s"),
                                {"full_task_name": full_task_name, "e": e})
              time.sleep(0)
  
          return idle_for
  