Python如何写一个多线程下可以使用的单例模式？

Question

Python如何写一个多线程下可以使用的单例模式？

Answer 1

import threading

class Singleton(object):

    INSTANCE = None

    lock = threading.RLock()

    def __new__(cls):
        cls.lock.acquire()
        if cls.INSTANCE is None:
            cls.INSTANCE = super(Singleton, cls).__new__(cls)
        cls.lock.release()
        return cls.INSTANCE


if __name__ == '__main__':
    a = Singleton()
    b = Singleton()
    print id(a)
    assert id(a) == id(b)

Answer 2

https://gist.github.com/werediver/4396488