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# 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]
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