Openstack Periodic Task

周期性任务在各个模块的manager.py（computer，scheduler，cell，network）中添加。

添加方法：在模块manager类实现中添加方法，并用装饰器periodic_task.periodic_task装饰。

实现机制

以ComputerManager类为例。

模块mananger类添加方法

在资源上报方法为例，装饰器指定该方法为周期性任务，并通过spacing参数指定任务执行间隔，不指定spacing参数则默认为60.0s。
nova.computer.manager.ComputerManager

@periodic_task.periodic_task(spacing=CONF.update_resources_interval)def update_available_resource…

periodic_task装饰器

periodic_task装饰器指明方法是周期性任务，并给周期性方法增加一些属性，包括周期型任务名称，任务执行间隔等。

oslo_service.periodic_task.periodic_task

def periodic_task(*args, **kwargs):
...

Manager类继承关系

nova.computer.manager.ComputerManager
nova.manager.Manager
nova.manager.PeriodicTask
oslo_service.periodic_task.PeriodicTask
PeriodicTask类对象通过元类PeriodicTasksMeta创建。

@six.add_metaclass(_PeriodicTasksMeta)
class PeriodicTasks(object):...

PeriodicTasksMeta元类

PeriodicTasksMeta元类收集模块manager类中定义的周期性任务，并保存在_periodic_tasks列表中。
oslo_service.PeriodicTasksMeta

DEFAULT_INTERVAL = 60.0
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:task._periodic_spacing = DEFAULT_INTERVALcls._periodic_tasks.append((name, task))cls._periodic_spacing[name] = task._periodic_spacingreturn True

def init(cls, names, bases, dict_):
　　 """Metaclass that allows us to collect decorated periodic tasks."""
　　…
　　for value in cls.__dict__.values():
　　　　if getattr(value, '_periodic_task', False):
　　　　　　cls._add_periodic_task(value)

触发执行周期性任务

Computer进程启动时调用service的start方法，start方法中创建定时器，定时执行periodic_tasks方法。
1、nova.service.Service.

class Service(service.Service):
"""Service object for binaries running on hosts.
def start(self):…if self.periodic_enable:if self.periodic_fuzzy_delay:initial_delay = random.randint(0, self.periodic_fuzzy_delay)else:initial_delay = Noneself.tg.add_dynamic_timer(self.periodic_tasks,initial_delay=initial_delay,periodic_interval_max=self.periodic_interval_max)
def periodic_tasks(self, raise_on_error=False):"""Tasks to be run at a periodic interval."""ctxt = context.get_admin_context()return self.manager.periodic_tasks(ctxt, raise_on_error=raise_on_error)

2、nova.manager.Manger

class Manager(base.Base, PeriodicTasks):def periodic_tasks(self, context, raise_on_error=False):"""Tasks to be run at a periodic interval."""return self.run_periodic_tasks(context, raise_on_error=raise_on_error)

3、oslo_service.periodic_task.PeriodicTask
run_periodic_tasks方法遍历执行_periodic_tasks中收集的周期性任务。

class PeriodicTasks(object):def run_periodic_tasks(self, context, raise_on_error=False):"""Tasks to be run at a periodic interval."""idle_for = DEFAULT_INTERVALfor task_name, task in self._periodic_tasks:if (task._periodic_external_ok and notself.conf.run_external_periodic_tasks):continuecls_name = reflection.get_class_name(self, fully_qualified=False)full_task_name = '.'.join([cls_name, task_name])spacing = self._periodic_spacing[task_name]last_run = self._periodic_last_run[task_name]# Check if due, if not skipidle_for = min(idle_for, spacing)if last_run is not None:delta = last_run + spacing - now()if delta > 0:idle_for = min(idle_for, delta)continueLOG.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:if raise_on_error:raiseLOG.exception(_LE("Error during %(full_task_name)s"),{"full_task_name": full_task_name})time.sleep(0)return idle_for