795aad12aa
This patch introduces a new backend system in oslo.service, enabling the dynamic loading of backends based on a configurable constant (`DEFAULT_BACKEND`). Key updates include: - A `get_backend()` method in `backend/__init__.py` to dynamically load backends based on the `DEFAULT_BACKEND` constant, which can be overridden at import time. - Validation of backends against an enumeration type to ensure correctness - Improved caching mechanism for loaded backends, reducing overhead during repeated calls to `get_backend()`. - Robust error handling for invalid or non-existent backend modules. - Unit tests covering: - Default backend behavior. - Cache functionality and invalidation. - Error handling for missing backend modules. - Retrieval of components from loaded backends. - Simplifies backend configuration by relying on a single constant that can be overridden at import time. - Ensures modularity and flexibility to support multiple backends like Eventlet and Threading. - Enhances testability through isolation and comprehensive mocks. - Maintains backward compatibility with the existing implementation while providing a clear migration path. This patch introduces the backend system without altering the current behavior of oslo.service, ensuring a seamless integration. Change-Id: I57a6371aea42d2dfc1ad06a0bbf60000e6682be3
82 lines
2.9 KiB
Python
82 lines
2.9 KiB
Python
# Copyright (C) 2024 Red Hat, Inc.
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#
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# Licensed under the Apache License, Version 2.0 (the "License");
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# you may not use this file except in compliance with the License.
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# You may obtain 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,
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# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or
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# implied.
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# See the License for the specific language governing permissions and
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# limitations under the License.
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from __future__ import annotations
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from abc import ABC
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from abc import abstractmethod
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from typing import Any
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from oslo_service.backend.exceptions import BackendComponentNotAvailable
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class BaseBackend(ABC):
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"""Base class for all backend implementations."""
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@abstractmethod
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def get_service_components(self) -> dict[str, Any]:
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"""Return the backend components.
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This method should return a dictionary containing all the components
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required for the backend to function. For example:
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{
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"ServiceLauncher": Class or function,
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"ProcessLauncher": Class or function,
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"Service": Class or function,
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"LoopingCall": Class or function,
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...
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}
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"""
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pass
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class ComponentRegistry:
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"""A registry to manage access to backend components.
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This class ensures that attempting to access a missing component
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raises an explicit error, improving clarity and debugging. It acts
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as a centralized registry for backend components.
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"""
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def __init__(self, components):
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"""Initialize the registry with a dictionary of components.
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:param components: A dictionary containing backend components, where
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the keys are component names and the values are
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the respective implementations.
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"""
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self._components = components
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def __getitem__(self, key):
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"""Retrieve a component by its key from the registry.
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:param key: The name of the component to retrieve.
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:raises NotImplementedError: If the component is
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not registered or available.
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:return: The requested component instance.
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"""
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if key not in self._components or self._components[key] is None:
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raise BackendComponentNotAvailable(
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f"Component '{key}' is not available in this backend.")
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return self._components[key]
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def __contains__(self, key):
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"""Check if a component is registered and available.
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:param key: The name of the component to check.
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:return: True if the component is registered
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and available, False otherwise.
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"""
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return key in self._components and self._components[key] is not None
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