# Copyright (c) 2017 Ansible Project # GNU General Public License v3.0+ (see COPYING or https://www.gnu.org/licenses/gpl-3.0.txt) # Make coding more python3-ish from __future__ import (absolute_import, division, print_function) __metaclass__ = type from threading import RLock class Singleton(type): """Metaclass for classes that wish to implement Singleton functionality. If an instance of the class exists, it's returned, otherwise a single instance is instantiated and returned. """ def __init__(cls, name, bases, dct): super(Singleton, cls).__init__(name, bases, dct) cls.__instance = None cls.__rlock = RLock() def __call__(cls, *args, **kw): if cls.__instance is not None: return cls.__instance with cls.__rlock: if cls.__instance is None: cls.__instance = super(Singleton, cls).__call__(*args, **kw) return cls.__instance