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OpenStack Study: dependency.py**** CubicPower OpenStack Study ****
# Copyright 2012 OpenStack Foundation # # 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. """This module provides support for dependency injection. Providers are registered via the 'provider' decorator, and dependencies on them are registered with 'requires' or 'optional'. Providers are available to their consumers via an attribute. See the documentation for the individual functions for more detail. See also: https://en.wikipedia.org/wiki/Dependency_injection """ import six from keystone import notifications from keystone.openstack.common.gettextutils import _ # flake8: noqa REGISTRY = {} _future_dependencies = {} _future_optionals = {} _factories = {}
**** CubicPower OpenStack Study **** class UnresolvableDependencyException(Exception): """An UnresolvableDependencyException is raised when a required dependency is not resolvable; see 'resolve_future_dependencies'. """
**** CubicPower OpenStack Study **** def __init__(self, name): msg = 'Unregistered dependency: %s' % name super(UnresolvableDependencyException, self).__init__(msg) def provider(name): """'provider' is a class decorator used to register providers. When 'provider' is used to decorate a class, members of that class will register themselves as providers for the named dependency. As an example, In the code fragment:: @dependency.provider('foo_api') class Foo: def __init__(self): ... ... foo = Foo() The object 'foo' will be registered as a provider for 'foo_api'. No more than one such instance should be created; additional instances will replace the previous ones, possibly resulting in different instances being used by different consumers. """
**** CubicPower OpenStack Study **** def provider(name): """'provider' is a class decorator used to register providers. When 'provider' is used to decorate a class, members of that class will register themselves as providers for the named dependency. As an example, In the code fragment:: @dependency.provider('foo_api') class Foo: def __init__(self): ... ... foo = Foo() The object 'foo' will be registered as a provider for 'foo_api'. No more than one such instance should be created; additional instances will replace the previous ones, possibly resulting in different instances being used by different consumers. """
**** CubicPower OpenStack Study **** def wrapper(cls): def wrapped(init): def register_event_callbacks(self): # NOTE(morganfainberg): A provider who has an implicit # dependency on other providers may utilize the event callback # mechanism to react to any changes in those providers. This is # performed at the .provider() mechanism so that we can ensure # that the callback is only ever called once and guaranteed # to be on the properly configured and instantiated backend. if not hasattr(self, 'event_callbacks'): return if not isinstance(self.event_callbacks, dict): msg = _('event_callbacks must be a dict') raise ValueError(msg) for event in self.event_callbacks: if not isinstance(self.event_callbacks[event], dict): msg = _('event_callbacks[%s] must be a dict') % event raise ValueError(msg) for resource_type in self.event_callbacks[event]: # Make sure we register the provider for each event it # cares to call back. callbacks = self.event_callbacks[event][resource_type] if not callbacks: continue if not hasattr(callbacks, '__iter__'): # ensure the callback information is a list # allowing multiple callbacks to exist callbacks = [callbacks] notifications.register_event_callback(event, resource_type, callbacks) def __wrapped_init__(self, *args, **kwargs): """Initialize the wrapped object and add it to the registry.""" init(self, *args, **kwargs) REGISTRY[name] = self register_event_callbacks(self) resolve_future_dependencies(name) return __wrapped_init__ cls.__init__ = wrapped(cls.__init__) _factories[name] = cls return cls return wrapper def _process_dependencies(obj): # Any dependencies that can be resolved immediately are resolved. # Dependencies that cannot be resolved immediately are stored for # resolution in resolve_future_dependencies.
**** CubicPower OpenStack Study **** def wrapped(init): def register_event_callbacks(self): # NOTE(morganfainberg): A provider who has an implicit # dependency on other providers may utilize the event callback # mechanism to react to any changes in those providers. This is # performed at the .provider() mechanism so that we can ensure # that the callback is only ever called once and guaranteed # to be on the properly configured and instantiated backend. if not hasattr(self, 'event_callbacks'): return if not isinstance(self.event_callbacks, dict): msg = _('event_callbacks must be a dict') raise ValueError(msg) for event in self.event_callbacks: if not isinstance(self.event_callbacks[event], dict): msg = _('event_callbacks[%s] must be a dict') % event raise ValueError(msg) for resource_type in self.event_callbacks[event]: # Make sure we register the provider for each event it # cares to call back. callbacks = self.event_callbacks[event][resource_type] if not callbacks: continue if not hasattr(callbacks, '__iter__'): # ensure the callback information is a list # allowing multiple callbacks to exist callbacks = [callbacks] notifications.register_event_callback(event, resource_type, callbacks) def __wrapped_init__(self, *args, **kwargs): """Initialize the wrapped object and add it to the registry.""" init(self, *args, **kwargs) REGISTRY[name] = self register_event_callbacks(self) resolve_future_dependencies(name) return __wrapped_init__ cls.__init__ = wrapped(cls.__init__) _factories[name] = cls return cls return wrapper def _process_dependencies(obj): # Any dependencies that can be resolved immediately are resolved. # Dependencies that cannot be resolved immediately are stored for # resolution in resolve_future_dependencies.
**** CubicPower OpenStack Study **** def process(obj, attr_name, unresolved_in_out): for dependency in getattr(obj, attr_name, []): if dependency not in REGISTRY: # We don't know about this dependency, so save it for later. unresolved_in_out.setdefault(dependency, []).append(obj) continue setattr(obj, dependency, REGISTRY[dependency]) process(obj, '_dependencies', _future_dependencies) process(obj, '_optionals', _future_optionals) def requires(*dependencies): """'requires' is a class decorator used to inject providers into consumers. The required providers will be made available to instances of the decorated class via an attribute with the same name as the provider. For example, in the code fragment:: @dependency.requires('foo_api', 'bar_api') class FooBarClient: def __init__(self): ... ... client = FooBarClient() The object 'client' will have attributes named 'foo_api' and 'bar_api', which are instances of the named providers. Objects must not rely on the existence of these attributes until after 'resolve_future_dependencies' has been called; they may not exist beforehand. Dependencies registered via 'required' must have providers - if not, an exception will be raised when 'resolve_future_dependencies' is called. """
**** CubicPower OpenStack Study **** def requires(*dependencies): """'requires' is a class decorator used to inject providers into consumers. The required providers will be made available to instances of the decorated class via an attribute with the same name as the provider. For example, in the code fragment:: @dependency.requires('foo_api', 'bar_api') class FooBarClient: def __init__(self): ... ... client = FooBarClient() The object 'client' will have attributes named 'foo_api' and 'bar_api', which are instances of the named providers. Objects must not rely on the existence of these attributes until after 'resolve_future_dependencies' has been called; they may not exist beforehand. Dependencies registered via 'required' must have providers - if not, an exception will be raised when 'resolve_future_dependencies' is called. """
**** CubicPower OpenStack Study **** def wrapper(self, *args, **kwargs): """Inject each dependency from the registry.""" self.__wrapped_init__(*args, **kwargs) _process_dependencies(self)
**** CubicPower OpenStack Study **** def wrapped(cls): """Note the required dependencies on the object for later injection. The dependencies of the parent class are combined with that of the child class to create a new set of dependencies. """ existing_dependencies = getattr(cls, '_dependencies', set()) cls._dependencies = existing_dependencies.union(dependencies) if not hasattr(cls, '__wrapped_init__'): cls.__wrapped_init__ = cls.__init__ cls.__init__ = wrapper return cls return wrapped def optional(*dependencies): """'optional' is the same as 'requires', except that the dependencies are optional - if no provider is available, the attributes will be set to None. """
**** CubicPower OpenStack Study **** def optional(*dependencies): """'optional' is the same as 'requires', except that the dependencies are optional - if no provider is available, the attributes will be set to None. """
**** CubicPower OpenStack Study **** def wrapper(self, *args, **kwargs): """Inject each dependency from the registry.""" self.__wrapped_init__(*args, **kwargs) _process_dependencies(self)
**** CubicPower OpenStack Study **** def wrapped(cls): """Note the optional dependencies on the object for later injection. The dependencies of the parent class are combined with that of the child class to create a new set of dependencies. """ existing_optionals = getattr(cls, '_optionals', set()) cls._optionals = existing_optionals.union(dependencies) if not hasattr(cls, '__wrapped_init__'): cls.__wrapped_init__ = cls.__init__ cls.__init__ = wrapper return cls return wrapped def resolve_future_dependencies(provider_name=None): """'resolve_future_dependencies' forces injection of all dependencies. Before this function is called, circular dependencies may not have been injected. This function should be called only once, after all global providers are registered. If an object needs to be created after this call, it must not have circular dependencies. If any required dependencies are unresolvable, this function will raise an UnresolvableDependencyException. Outside of this module, this function should be called with no arguments; the optional argument is used internally, and should be treated as an implementation detail. """ new_providers = dict() if provider_name: # A provider was registered, so take care of any objects depending on # it. targets = _future_dependencies.pop(provider_name, []) targets.extend(_future_optionals.pop(provider_name, [])) for target in targets: setattr(target, provider_name, REGISTRY[provider_name]) return # Resolve optional dependencies, sets the attribute to None if there's no # provider registered. for dependency, targets in six.iteritems(_future_optionals.copy()): provider = REGISTRY.get(dependency) if provider is None: factory = _factories.get(dependency) if factory: provider = factory() REGISTRY[dependency] = provider new_providers[dependency] = provider for target in targets: setattr(target, dependency, provider) # Resolve future dependencies, raises UnresolvableDependencyException if # there's no provider registered. try: for dependency, targets in six.iteritems(_future_dependencies.copy()): if dependency not in REGISTRY: # a Class was registered that could fulfill the dependency, but # it has not yet been initialized. factory = _factories.get(dependency) if factory: provider = factory() REGISTRY[dependency] = provider new_providers[dependency] = provider else: raise UnresolvableDependencyException(dependency) for target in targets: setattr(target, dependency, REGISTRY[dependency]) finally: _future_dependencies.clear() return new_providers def reset(): """Reset the registry of providers. This is useful for unit testing to ensure that tests don't use providers from previous tests. """ REGISTRY.clear() _future_dependencies.clear() _future_optionals.clear()
**** CubicPower OpenStack Study **** def resolve_future_dependencies(provider_name=None): """'resolve_future_dependencies' forces injection of all dependencies. Before this function is called, circular dependencies may not have been injected. This function should be called only once, after all global providers are registered. If an object needs to be created after this call, it must not have circular dependencies. If any required dependencies are unresolvable, this function will raise an UnresolvableDependencyException. Outside of this module, this function should be called with no arguments; the optional argument is used internally, and should be treated as an implementation detail. """ new_providers = dict() if provider_name: # A provider was registered, so take care of any objects depending on # it. targets = _future_dependencies.pop(provider_name, []) targets.extend(_future_optionals.pop(provider_name, [])) for target in targets: setattr(target, provider_name, REGISTRY[provider_name]) return # Resolve optional dependencies, sets the attribute to None if there's no # provider registered. for dependency, targets in six.iteritems(_future_optionals.copy()): provider = REGISTRY.get(dependency) if provider is None: factory = _factories.get(dependency) if factory: provider = factory() REGISTRY[dependency] = provider new_providers[dependency] = provider for target in targets: setattr(target, dependency, provider) # Resolve future dependencies, raises UnresolvableDependencyException if # there's no provider registered. try: for dependency, targets in six.iteritems(_future_dependencies.copy()): if dependency not in REGISTRY: # a Class was registered that could fulfill the dependency, but # it has not yet been initialized. factory = _factories.get(dependency) if factory: provider = factory() REGISTRY[dependency] = provider new_providers[dependency] = provider else: raise UnresolvableDependencyException(dependency) for target in targets: setattr(target, dependency, REGISTRY[dependency]) finally: _future_dependencies.clear() return new_providers
**** CubicPower OpenStack Study **** def reset(): """Reset the registry of providers. This is useful for unit testing to ensure that tests don't use providers from previous tests. """ REGISTRY.clear() _future_dependencies.clear() _future_optionals.clear()
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