cf6d43d774
This patch adds exception handling when calling pre and post functions of hooks. Exceptions will be caught and logged, but the hook chain and function call will be allowed to proceed. Partially implements: bp instance-network-info-hook Change-Id: I45e76cd156c244ff57f77db103a9a579f14ad4f1
143 lines
4.6 KiB
Python
143 lines
4.6 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 nova.openstack.common.gettextutils import _LE
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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 FatalHookException(Exception):
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"""Exception which should be raised by hooks to indicate that normal
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execution of the hooked function should be terminated. Raised exception
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will be logged and reraised.
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"""
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pass
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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, f=None):
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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",
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{'name': name, 'obj': obj})
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try:
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if f:
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pre(f, *args, **kwargs)
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else:
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pre(*args, **kwargs)
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except FatalHookException:
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msg = _LE("Fatal Exception running %(name)s "
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"pre-hook: %(obj)s")
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LOG.exception(msg, {'name': name, 'obj': obj})
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raise
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except Exception:
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msg = _LE("Exception running %(name)s pre-hook: %(obj)s")
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LOG.exception(msg, {'name': name, 'obj': obj})
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def run_post(self, name, rv, args, kwargs, f=None):
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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",
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{'name': name, 'obj': obj})
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try:
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if f:
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post(f, rv, *args, **kwargs)
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else:
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post(rv, *args, **kwargs)
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except FatalHookException:
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msg = _LE("Fatal Exception running %(name)s "
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"post-hook: %(obj)s")
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LOG.exception(msg, {'name': name, 'obj': obj})
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raise
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except Exception:
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msg = _LE("Exception running %(name)s post-hook: %(obj)s")
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LOG.exception(msg, {'name': name, 'obj': obj})
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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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f.__hook_name__ = name
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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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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 reset():
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"""Clear loaded hooks."""
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_HOOKS.clear()
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