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# Copyright (C) 2024 Red Hat, Inc.
#
# 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.
from __future__ import annotations
import abc
from typing import Any
from oslo_service.backend.exceptions import BackendComponentNotAvailable
class BaseBackend(abc.ABC):
"""Base class for all backend implementations."""
@abc.abstractmethod
def get_service_components(self) -> dict[str, Any]:
"""Return the backend components.
This method should return a dictionary containing all the components
required for the backend to function. For example:
{
"ServiceLauncher": Class or function,
"ProcessLauncher": Class or function,
"Service": Class or function,
"LoopingCall": Class or function,
...
}
"""
pass
class ServiceBase(metaclass=abc.ABCMeta):
"""Base class for all services."""
@abc.abstractmethod
def start(self):
"""Start service."""
@abc.abstractmethod
def stop(self):
"""Stop service."""
@abc.abstractmethod
def wait(self):
"""Wait for service to complete."""
@abc.abstractmethod
def reset(self):
"""Reset service.
Called in case a service running in daemon mode receives SIGHUP.
"""
class ComponentRegistry:
"""A registry to manage access to backend components.
This class ensures that attempting to access a missing component
raises an explicit error, improving clarity and debugging. It acts
as a centralized registry for backend components.
"""
def __init__(self, components):
"""Initialize the registry with a dictionary of components.
:param components: A dictionary containing backend components,
where the keys are component names and the values are the
respective implementations.
"""
self._components = components
def __getitem__(self, key):
"""Retrieve a component by its key from the registry.
:param key: The name of the component to retrieve.
:raises NotImplementedError: If the component is not registered
or available.
:return: The requested component instance.
"""
if key not in self._components or self._components[key] is None:
raise BackendComponentNotAvailable(
f"Component '{key}' is not available in this backend.")
return self._components[key]
def __contains__(self, key):
"""Check if a component is registered and available.
:param key: The name of the component to check.
:return: True if the component is registered and available,
False otherwise.
"""
return key in self._components and self._components[key] is not None
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