| # Copyright (c) 2020, NVIDIA CORPORATION. All rights reserved. | |
| # | |
| # 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. | |
| import threading | |
| class Singleton(type): | |
| """ Implementation of a generic, tread-safe singleton meta-class. | |
| Can be used as meta-class, i.e. will create | |
| """ | |
| # List of instances - one per class. | |
| __instances = {} | |
| # Lock used for accessing the instance. | |
| __lock = threading.Lock() | |
| def __call__(cls, *args, **kwargs): | |
| """ Returns singleton instance. A thread safe implementation. """ | |
| if cls not in cls.__instances: | |
| # Enter critical section. | |
| with cls.__lock: | |
| # Check once again. | |
| if cls not in cls.__instances: | |
| # Create a new object instance - one per class. | |
| cls.__instances[cls] = super(Singleton, cls).__call__(*args, **kwargs) | |
| # Return the instance. | |
| return cls.__instances[cls] | |