28 lines
865 B
Python
28 lines
865 B
Python
# Copyright (c) 2017 Ansible Project
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# GNU General Public License v3.0+ (see COPYING or https://www.gnu.org/licenses/gpl-3.0.txt)
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from __future__ import annotations
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from threading import RLock
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class Singleton(type):
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"""Metaclass for classes that wish to implement Singleton
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functionality. If an instance of the class exists, it's returned,
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otherwise a single instance is instantiated and returned.
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"""
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def __init__(cls, name, bases, dct):
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super(Singleton, cls).__init__(name, bases, dct)
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cls.__instance = None
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cls.__rlock = RLock()
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def __call__(cls, *args, **kw):
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if cls.__instance is not None:
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return cls.__instance
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with cls.__rlock:
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if cls.__instance is None:
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cls.__instance = super(Singleton, cls).__call__(*args, **kw)
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return cls.__instance
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