30 lines
1.0 KiB
Python
30 lines
1.0 KiB
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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# FIXME: object identity/singleton-ness does not appear to survive pickle roundtrip (eg, copy.copy, copy.deepcopy), implement __reduce_ex__ and __copy__?
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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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