143 lines
4.6 KiB
Python
143 lines
4.6 KiB
Python
# 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::
|
|
|
|
| class MyHook(object):
|
|
| def pre(self, *args, **kwargs):
|
|
| # do stuff before wrapped callable runs
|
|
|
|
|
| def post(self, rv, *args, **kwargs):
|
|
| # do stuff after wrapped callable runs
|
|
|
|
Example Hook object with function parameters::
|
|
|
|
| class MyHookWithFunction(object):
|
|
| def pre(self, f, *args, **kwargs):
|
|
| # do stuff with wrapped function info
|
|
| def post(self, f, *args, **kwargs):
|
|
| # do stuff with wrapped function info
|
|
|
|
"""
|
|
|
|
import functools
|
|
|
|
import stevedore
|
|
|
|
from nova.i18n import _LE
|
|
from nova.openstack.common import log as logging
|
|
|
|
LOG = logging.getLogger(__name__)
|
|
NS = 'nova.hooks'
|
|
|
|
_HOOKS = {} # hook name => hook manager
|
|
|
|
|
|
class FatalHookException(Exception):
|
|
"""Exception which should be raised by hooks to indicate that normal
|
|
execution of the hooked function should be terminated. Raised exception
|
|
will be logged and reraised.
|
|
"""
|
|
pass
|
|
|
|
|
|
class HookManager(stevedore.hook.HookManager):
|
|
def __init__(self, name):
|
|
# invoke_on_load creates an instance of the Hook class
|
|
super(HookManager, self).__init__(NS, name, invoke_on_load=True)
|
|
|
|
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})
|
|
try:
|
|
if f:
|
|
pre(f, *args, **kwargs)
|
|
else:
|
|
pre(*args, **kwargs)
|
|
except FatalHookException:
|
|
msg = _LE("Fatal Exception running %(name)s "
|
|
"pre-hook: %(obj)s")
|
|
LOG.exception(msg, {'name': name, 'obj': obj})
|
|
raise
|
|
except Exception:
|
|
msg = _LE("Exception running %(name)s pre-hook: %(obj)s")
|
|
LOG.exception(msg, {'name': name, 'obj': obj})
|
|
|
|
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})
|
|
try:
|
|
if f:
|
|
post(f, rv, *args, **kwargs)
|
|
else:
|
|
post(rv, *args, **kwargs)
|
|
except FatalHookException:
|
|
msg = _LE("Fatal Exception running %(name)s "
|
|
"post-hook: %(obj)s")
|
|
LOG.exception(msg, {'name': name, 'obj': obj})
|
|
raise
|
|
except Exception:
|
|
msg = _LE("Exception running %(name)s post-hook: %(obj)s")
|
|
LOG.exception(msg, {'name': name, 'obj': obj})
|
|
|
|
|
|
def add_hook(name, pass_function=False):
|
|
"""Execute optional pre and post methods around the decorated
|
|
function. This is useful for customization around callables.
|
|
"""
|
|
|
|
def outer(f):
|
|
f.__hook_name__ = name
|
|
|
|
@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()
|