aabc213040
Currently tox ignores D401 (401: First line should be in imperative mood). This change removes it and make keystoneauth docstring compliantwith it. Change-Id: I136cf810f47c4c19f29216907a63f226930b5082 Partial-Bug: 1570049
231 lines
7.5 KiB
Python
231 lines
7.5 KiB
Python
# Copyright 2012 OpenStack Foundation
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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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"""This module provides support for dependency injection.
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Providers are registered via the ``@provider()`` decorator, and dependencies on
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them are registered with ``@requires()``. Providers are available to their
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consumers via an attribute. See the documentation for the individual functions
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for more detail.
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See also:
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https://en.wikipedia.org/wiki/Dependency_injection
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"""
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import traceback
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from keystone.i18n import _
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_REGISTRY = {}
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_future_dependencies = {}
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_factories = {}
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def _set_provider(name, provider):
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_original_provider, where_registered = _REGISTRY.get(name, (None, None))
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if where_registered:
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raise Exception('%s already has a registered provider, at\n%s' %
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(name, ''.join(where_registered)))
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_REGISTRY[name] = (provider, traceback.format_stack())
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GET_REQUIRED = object()
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GET_OPTIONAL = object()
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def get_provider(name, optional=GET_REQUIRED):
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if optional is GET_REQUIRED:
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return _REGISTRY[name][0]
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return _REGISTRY.get(name, (None, None))[0]
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class UnresolvableDependencyException(Exception):
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"""Raised when a required dependency is not resolvable.
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See ``resolve_future_dependencies()`` for more details.
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"""
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def __init__(self, name, targets):
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msg = _('Unregistered dependency: %(name)s for %(targets)s') % {
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'name': name, 'targets': targets}
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super(UnresolvableDependencyException, self).__init__(msg)
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def provider(name):
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"""A class decorator used to register providers.
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When ``@provider()`` is used to decorate a class, members of that class
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will register themselves as providers for the named dependency. As an
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example, In the code fragment::
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@dependency.provider('foo_api')
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class Foo:
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def __init__(self):
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...
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...
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foo = Foo()
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The object ``foo`` will be registered as a provider for ``foo_api``. No
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more than one such instance should be created; additional instances will
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replace the previous ones, possibly resulting in different instances being
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used by different consumers.
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"""
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def wrapper(cls):
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def wrapped(init):
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def __wrapped_init__(self, *args, **kwargs):
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"""Initialize the wrapped object and add it to the registry."""
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init(self, *args, **kwargs)
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_set_provider(name, self)
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resolve_future_dependencies(__provider_name=name)
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return __wrapped_init__
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cls.__init__ = wrapped(cls.__init__)
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_factories[name] = cls
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return cls
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return wrapper
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def _process_dependencies(obj):
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# Any dependencies that can be resolved immediately are resolved.
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# Dependencies that cannot be resolved immediately are stored for
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# resolution in resolve_future_dependencies.
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def process(obj, attr_name, unresolved_in_out):
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for dependency in getattr(obj, attr_name, []):
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if dependency not in _REGISTRY:
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# We don't know about this dependency, so save it for later.
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unresolved_in_out.setdefault(dependency, []).append(obj)
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continue
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setattr(obj, dependency, get_provider(dependency))
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process(obj, '_dependencies', _future_dependencies)
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def requires(*dependencies):
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"""A class decorator used to inject providers into consumers.
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The required providers will be made available to instances of the decorated
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class via an attribute with the same name as the provider. For example, in
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the code fragment::
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@dependency.requires('foo_api', 'bar_api')
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class FooBarClient:
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def __init__(self):
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...
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...
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client = FooBarClient()
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The object ``client`` will have attributes named ``foo_api`` and
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``bar_api``, which are instances of the named providers.
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Objects must not rely on the existence of these attributes until after
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``resolve_future_dependencies()`` has been called; they may not exist
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beforehand.
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Dependencies registered via ``@required()`` must have providers; if not,
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an ``UnresolvableDependencyException`` will be raised when
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``resolve_future_dependencies()`` is called.
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"""
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def wrapper(self, *args, **kwargs):
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"""Inject each dependency from the registry."""
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self.__wrapped_init__(*args, **kwargs)
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_process_dependencies(self)
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def wrapped(cls):
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"""Note the required dependencies on the object for later injection.
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The dependencies of the parent class are combined with that of the
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child class to create a new set of dependencies.
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"""
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existing_dependencies = getattr(cls, '_dependencies', set())
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cls._dependencies = existing_dependencies.union(dependencies)
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if not hasattr(cls, '__wrapped_init__'):
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cls.__wrapped_init__ = cls.__init__
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cls.__init__ = wrapper
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return cls
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return wrapped
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def resolve_future_dependencies(__provider_name=None):
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"""Force injection of all dependencies.
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Before this function is called, circular dependencies may not have been
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injected. This function should be called only once, after all global
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providers are registered. If an object needs to be created after this
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call, it must not have circular dependencies.
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If any required dependencies are unresolvable, this function will raise an
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``UnresolvableDependencyException``.
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Outside of this module, this function should be called with no arguments;
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the optional argument, ``__provider_name`` is used internally, and should
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be treated as an implementation detail.
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"""
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new_providers = dict()
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if __provider_name:
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# A provider was registered, so take care of any objects depending on
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# it.
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targets = _future_dependencies.pop(__provider_name, [])
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for target in targets:
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setattr(target, __provider_name, get_provider(__provider_name))
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return
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# Resolve future dependencies, raises UnresolvableDependencyException if
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# there's no provider registered.
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try:
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for dependency, targets in _future_dependencies.copy().items():
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if dependency not in _REGISTRY:
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# a Class was registered that could fulfill the dependency, but
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# it has not yet been initialized.
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factory = _factories.get(dependency)
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if factory:
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provider = factory()
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new_providers[dependency] = provider
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else:
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raise UnresolvableDependencyException(dependency, targets)
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for target in targets:
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setattr(target, dependency, get_provider(dependency))
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finally:
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_future_dependencies.clear()
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return new_providers
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def reset():
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"""Reset the registry of providers.
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This is useful for unit testing to ensure that tests don't use providers
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from previous tests.
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"""
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_REGISTRY.clear()
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_future_dependencies.clear()
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