多线程下,使用new实现单例

import threading

class Test(object):
    from threading import Lock

    lock = Lock()
    flag = None

    def __new__(cls, *args, **kwargs):
        with cls.lock:
            if cls.flag is None:
                cls.flag = super().__new__(cls)
        return cls.flag

def func():
    res = Test()
    print(res)

t = threading.Thread(target=func).start()
t2 = threading.Thread(target=func).start()

#<__main__.Msg object at 0x00000193A9C3A198>
#<__main__.Msg object at 0x00000193A9C3A198>