165 lines
5.2 KiB
Python
165 lines
5.2 KiB
Python
# Copyright (c) 2012 OpenStack Foundation
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# All Rights Reserved.
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#
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# Licensed under the Apache License, Version 2.0 (the "License"); you may
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# not use this file except in compliance with the License. You may obtain
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# a copy of the License at
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#
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# http://www.apache.org/licenses/LICENSE-2.0
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#
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# Unless required by applicable law or agreed to in writing, software
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# distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
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# WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
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# License for the specific language governing permissions and limitations
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# under the License.
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"""Decorator and config option definitions for adding custom code (hooks)
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around callables.
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Any method may have the 'add_hook' decorator applied, which yields the
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ability to invoke Hook objects before or after the method. (i.e. pre and
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post)
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Hook objects are loaded by HookLoaders. Each named hook may invoke multiple
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Hooks.
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Example Hook object:
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class MyHook(object):
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def pre(self, *args, **kwargs):
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# do stuff before wrapped callable runs
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def post(self, rv, *args, **kwargs):
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# do stuff after wrapped callable runs
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Example Hook object with function parameters:
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class MyHookWithFunction(object):
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def pre(self, f, *args, **kwargs):
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# do stuff with wrapped function info
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def post(self, f, *args, **kwards):
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# do stuff with wrapped function info
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"""
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import functools
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import stevedore
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from openstack.common.gettextutils import _, _LE
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from openstack.common import log as logging
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LOG = logging.getLogger(__name__)
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NS = 'openstack.common.hooks'
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_HOOKS = {} # hook name => hook manager
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class HookManager(object):
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"""Hook manager class for manipulating hooks.
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Coordinate execution of multiple extensions using a common name.
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"""
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def __init__(self, name):
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"""Invoke_on_load creates an instance of the Hook class
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:param name: The name of the hooks to load.
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:type name: str
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"""
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self.api = stevedore.hook.HookManager(NS, name, invoke_on_load=True)
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@property
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def extensions(self):
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return self.api.extensions
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def _run(self, name, method_type, args, kwargs, func):
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if method_type not in ('pre', 'post'):
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msg = _("Wrong type of hook method. "
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"Only 'pre' and 'post' type allowed")
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raise ValueError(msg)
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for extension in self.api.extensions:
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obj = extension.obj
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hook_method = getattr(obj, method_type, None)
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if hook_method:
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msg = ("Running %(name)s %(type)s-hook: %(obj)s" %
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{'name': name, 'type': method_type, 'obj': obj})
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LOG.debug(msg)
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try:
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if func:
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hook_method(func, *args, **kwargs)
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else:
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hook_method(*args, **kwargs)
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except Exception:
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LOG.exception(_LE('Error during %s-hook') % method_type)
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def run_pre(self, name, args, kwargs, f=None):
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"""Execute optional pre methods of loaded hooks.
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:param name: The name of the loaded hooks.
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:param args: Positional arguments which would be transmitted into
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all pre methods of loaded hooks.
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:param kwargs: Keyword args which would be transmitted into all pre
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methods of loaded hooks.
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:param f: Target function.
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"""
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self._run(name=name, method_type='pre', args=args, kwargs=kwargs,
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func=f)
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def run_post(self, name, rv, args, kwargs, f=None):
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"""Execute optional post methods of loaded hooks.
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:param name: The name of the loaded hooks.
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:param rv: Return values of target method call.
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:param args: Positional arguments which would be transmitted into
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all post methods of loaded hooks.
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:param kwargs: Keyword args which would be transmitted into all post
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methods of loaded hooks.
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:param f: Target function.
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"""
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self._run(name=name, method_type='post', args=(rv,) + args,
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kwargs=kwargs, func=f)
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def add_hook(name, pass_function=False):
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"""Execute optional pre and post methods around the decorated
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function. This is useful for customization around callables.
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"""
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def outer(f):
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@functools.wraps(f)
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def inner(*args, **kwargs):
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manager = get_hook(name)
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function = None
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if pass_function:
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function = f
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manager.run_pre(name, args, kwargs, f=function)
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rv = f(*args, **kwargs)
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manager.run_post(name, rv, args, kwargs, f=function)
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return rv
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return inner
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return outer
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def get_hook(hook_name):
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"""Return HookManager by name.
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Checks for the existence HookManager by given name.
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If there is no suitable HookManager, it will be created.
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Then the desired HookManager will be returned.
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"""
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if hook_name not in _HOOKS:
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_HOOKS[hook_name] = HookManager(hook_name)
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return _HOOKS[hook_name]
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def reset():
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"""Clear loaded hooks."""
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_HOOKS.clear()
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