e937a53065
Hooks add the ability to insert custom code around operations that
declare a named hook:
e.g.
@hooks.add_hooks('create_instance')
def create_instance(....):
....
The above hook allows Hook objects to be run 'pre' and 'post' the
execution of create_instance()
Hook objects are discovered via the setuptools entry point group
'nova.hooks'.
Change-Id: I3961df12ef415085de7459438967edacc34500c2
97 lines
2.7 KiB
Python
97 lines
2.7 KiB
Python
# vim: tabstop=4 shiftwidth=4 softtabstop=4
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# Copyright (c) 2012 OpenStack, LLC.
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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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"""
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import functools
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import stevedore
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from nova.openstack.common import log as logging
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LOG = logging.getLogger(__name__)
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NS = 'nova.hooks'
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_HOOKS = {} # hook name => hook manager
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class HookManager(stevedore.hook.HookManager):
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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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super(HookManager, self).__init__(NS, name, invoke_on_load=True)
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def run_pre(self, name, args, kwargs):
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for e in self.extensions:
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obj = e.obj
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pre = getattr(obj, 'pre', None)
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if pre:
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LOG.debug(_("Running %(name)s pre-hook: %(obj)s") % locals())
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pre(*args, **kwargs)
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def run_post(self, name, rv, args, kwargs):
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for e in reversed(self.extensions):
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obj = e.obj
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post = getattr(obj, 'post', None)
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if post:
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LOG.debug(_("Running %(name)s post-hook: %(obj)s") % locals())
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post(rv, *args, **kwargs)
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def add_hook(name):
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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 = _HOOKS.setdefault(name, HookManager(name))
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manager.run_pre(name, args, kwargs)
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rv = f(*args, **kwargs)
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manager.run_post(name, rv, args, kwargs)
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return rv
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return inner
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return outer
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def reset():
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"""Clear loaded hooks."""
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_HOOKS.clear()
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