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# Copyright (c) 2022, Dell Inc. or its subsidiaries. All rights reserved.
# SPDX-License-Identifier: Apache-2.0
# See the LICENSE file for details.
#
# This file is part of NVMe STorage Appliance Services (nvme-stas).
#
# Authors: Martin Belanger <Martin.Belanger@dell.com>
#
'''Implementation of a singleton pattern'''
class Singleton(type):
'''metaclass implementation of a singleton pattern'''
_instances = {}
def __call__(cls, *args, **kwargs):
if cls not in cls._instances:
# This variable declaration is required to force a
# strong reference on the instance.
instance = super(Singleton, cls).__call__(*args, **kwargs)
cls._instances[cls] = instance
return cls._instances[cls]
def destroy(cls):
'''Delete a singleton instance.
This is to be invoked using the derived class Name.
For example:
class Child(Singleton):
pass
child1 = Child() # Instantiate singleton
child2 = Child() # Get a reference to the singleton
print(f'{child1 is child2}') # True
Child.destroy() # Delete the singleton
print(f'{child1 is child2}') # Still True because child1 and child2 still hold reference to the singleton
child1 = Child() # Instantiate a new singleton and assign to child1
print(f'{child1 is child2}') # False
'''
cls._instances.pop(cls, None)
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