pyhon __new__单例2.py

# class Singleton:
#     _instance = None
#
#     def __init__(self):
#         print("init")
#
#     @classmethod
#     def get_instance(cls):
#         if cls._instance is None:
#             cls._instance =cls()
#         return cls._instance
#
#
# if __name__ == "__main__":
#     a = Singleton.get_instance()
#     b = Singleton.get_instance()
#
#     print(a is b)

"""
运行结果
init
True

 这是一个实现方法，获取当前实例，但是可以正常实例化它，因此它不会成为单例对象。

"""

# 使用__new__ 创建实例，在创建类实例的时候会调用此方法，此方法在__init__之前已经调用过。
#
# class Singleton:
#     _instance =None
#
#     def __init__(self):
#         print("init")
#
#     def __new__(cls, *args, **kwargs):
#         if cls._instance is None:
#             cls._instance = super().__new__(cls)
#         return cls._instance
#
#
# if __name__ == '__main__':
#     a = Singleton()
#     b = Singleton()
#     print(a is b)  # True

# 以上两种方式都不是线程安全 ，淫才十七称为线程安全，让我们LOCK y引入

import threading
import time
class ThreadingSingleton:
    _instance =None
    _lock=threading.Lock()
    def __init__(self,name):
        time.sleep(3)
        self.name= name
        # print("init")
    def __new__(cls, *args, **kwargs):
        with cls._lock:
            if cls._instance is None:
                cls._instance =super().__new__(cls)
            return cls._instance
    def __str__(self):
        return str(self.name)

if __name__ == '__main__':

    for i in range(10):
        # print("i", i)
        my = ThreadingSingleton(i)
        print(my)

# 简单实用也安全实现线程模式，在初始化的时候 停止三秒 线程依然按照顺序执行，。

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