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OpenStack Study: hooks.py**** CubicPower OpenStack Study ****
# Copyright (c) 2012 OpenStack Foundation # All Rights Reserved. # # 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. """Decorator and config option definitions for adding custom code (hooks) around callables. Any method may have the 'add_hook' decorator applied, which yields the ability to invoke Hook objects before or after the method. (i.e. pre and post) Hook objects are loaded by HookLoaders. Each named hook may invoke multiple Hooks. Example Hook object:
**** CubicPower OpenStack Study **** class MyHook(object):
**** CubicPower OpenStack Study **** def pre(self, *args, **kwargs): # do stuff before wrapped callable runs
**** CubicPower OpenStack Study **** def post(self, rv, *args, **kwargs): # do stuff after wrapped callable runs Example Hook object with function parameters:
**** CubicPower OpenStack Study **** class MyHookWithFunction(object):
**** CubicPower OpenStack Study **** def pre(self, f, *args, **kwargs): # do stuff with wrapped function info
**** CubicPower OpenStack Study **** def post(self, f, *args, **kwards): # do stuff with wrapped function info """ import functools import stevedore from nova.openstack.common.gettextutils import _ from nova.openstack.common import log as logging LOG = logging.getLogger(__name__) NS = 'nova.hooks' _HOOKS = {} # hook name => hook manager
**** CubicPower OpenStack Study **** class HookManager(stevedore.hook.HookManager):
**** CubicPower OpenStack Study **** def __init__(self, name): # invoke_on_load creates an instance of the Hook class super(HookManager, self).__init__(NS, name, invoke_on_load=True)
**** CubicPower OpenStack Study **** def run_pre(self, name, args, kwargs, f=None): for e in self.extensions: obj = e.obj pre = getattr(obj, 'pre', None) if pre: LOG.debug(_("Running %(name)s pre-hook: %(obj)s"), {'name': name, 'obj': obj}) if f: pre(f, *args, **kwargs) else: pre(*args, **kwargs)
**** CubicPower OpenStack Study **** def run_post(self, name, rv, args, kwargs, f=None): for e in reversed(self.extensions): obj = e.obj post = getattr(obj, 'post', None) if post: LOG.debug(_("Running %(name)s post-hook: %(obj)s"), {'name': name, 'obj': obj}) if f: post(f, rv, *args, **kwargs) else: post(rv, *args, **kwargs) def add_hook(name, pass_function=False): """Execute optional pre and post methods around the decorated function. This is useful for customization around callables. """
**** CubicPower OpenStack Study **** def add_hook(name, pass_function=False): """Execute optional pre and post methods around the decorated function. This is useful for customization around callables. """
**** CubicPower OpenStack Study **** def outer(f): @functools.wraps(f) def inner(*args, **kwargs): manager = _HOOKS.setdefault(name, HookManager(name)) function = None if pass_function: function = f manager.run_pre(name, args, kwargs, f=function) rv = f(*args, **kwargs) manager.run_post(name, rv, args, kwargs, f=function) return rv return inner return outer def reset(): """Clear loaded hooks.""" _HOOKS.clear()
**** CubicPower OpenStack Study **** def inner(*args, **kwargs): manager = _HOOKS.setdefault(name, HookManager(name)) function = None if pass_function: function = f manager.run_pre(name, args, kwargs, f=function) rv = f(*args, **kwargs) manager.run_post(name, rv, args, kwargs, f=function) return rv return inner return outer def reset(): """Clear loaded hooks.""" _HOOKS.clear()
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