9773a1f289
* Add a Singleton class, use it with Display * update six import * Move remaining failes to display singleton * Fix rebase issues * Singleton improvements * Add code-smell for 'from __main__ import display'. ci_complete * s/self/cls/g * Add docs for no-main-display * Address linting issues * Add changelog fragment. ci_complete * Implement reentrant lock for class instantiation in Singleton * Add Display singleton porting guide
30 lines
949 B
Python
30 lines
949 B
Python
# 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
|