class _PluginDirectory(object):"""A directory of activated plugins in a Neutron Deployment.The directory is bootstrapped by a Neutron Manager running inthe context of a Neutron Server process."""def __init__(self):self._plugins = {}                         # 构造函数只是对_plugins属性进行了初始化。def add_plugin(self, alias, plugin):"""Add a plugin of type 'alias'."""self._plugins[alias] = plugindef get_plugin(self, alias):"""Get a plugin for a given alias or None if not present."""p = self._plugins.get(alias)return weakref.proxy(p) if p else None     # 如果没有名为alias的plugin，返回None。否则返回对应plugin的弱引用。
@propertydef plugins(self):                             # _PluginDirectory的plugins属性是一个函数，返回各个plugin的弱引用。"""The mapping alias -> weak reference to the plugin."""return dict((x, weakref.proxy(y))for x, y in self._plugins.items())@propertydef unique_plugins(self):"""A sequence of the unique plugins activated in the environments."""return tuple(weakref.proxy(x) for x in set(self._plugins.values()))@propertydef is_loaded(self):"""True if the directory is non empty."""return len(self._plugins) > 0

@six.add_metaclass(profiler.TracedMeta)
class NeutronManager(object):"""Neutron's Manager class.Neutron's Manager class is responsible for parsing a config file andinstantiating the correct plugin that concretely implementsneutron_plugin_base class."""@classmethod@utils.synchronized("manager")def _create_instance(cls):if not cls.has_instance():cls._instance = cls()@classmethoddef has_instance(cls):return cls._instance is not None@classmethoddef get_instance(cls):# double checked lockingif not cls.has_instance():cls._create_instance()return cls._instance

@six.add_metaclass(profiler.TracedMeta)
class NeutronManager(object):_instance = Nonedef __init__(self, options=None, config_file=None):# If no options have been provided, create an empty dictif not options:options = {}""" 检查配置文件中是否配置了core_plugin,否则抛出异常 """msg = validate_pre_plugin_load()if msg:LOG.critical(msg)raise Exception(msg)# NOTE(jkoelker) Testing for the subclass with the __subclasshook__#                breaks tach monitoring. It has been removed#                intentionally to allow v2 plugins to be monitored#                for performance metrics.plugin_provider = cfg.CONF.core_plugin                      # 从配置文件中获取core_plugin，一般为ml2LOG.info(_LI("Loading core plugin: %s"), plugin_provider)   # server.log中打印 INFO neutron.manager [-] Loading core plugin: ml2# NOTE(armax): keep hold of the actual plugin objectplugin = self._get_plugin_instance(CORE_PLUGINS_NAMESPACE,  # 通过namespace和plugin_provider获取plugin。
                                           plugin_provider)directory.add_plugin(lib_const.CORE, plugin)                # 添加core_plugin（Ml2Plugin的实例）到_PLUGIN_DIRECTORY._plugins中。""" 检查配置文件中的dhcp_agents_per_network,否则抛出异常 """msg = validate_post_plugin_load()if msg:LOG.critical(msg)raise Exception(msg)# load services from the core plugin first
        self._load_services_from_core_plugin(plugin)self._load_service_plugins()                                # 加载service_plugins，包括配置文件中指定的和默认的。# Used by pecan WSGIself.resource_plugin_mappings = {}self.resource_controller_mappings = {}self.path_prefix_resource_mappings = defaultdict(list)

class NeutronManager(object):def _get_plugin_instance(self, namespace, plugin_provider):                 # 通过不同的namespace中的plugin_provider获取相应的plugin。plugin_class = self.load_class_for_provider(namespace, plugin_provider) # 调用load_class_for_provider函数来返回Plugin类。return plugin_class()                                                   # 实例化Plugin类，在此处完成各个plugin的__init__方法的调用。