python 单例模式 线程安全

import threading

_lock = threading.Lock()


class Single(object):
    def __new__(cls, *args, **kwargs):
        if not hasattr(Single, "_instance"):
            with _lock:
                if not hasattr(Single, "_instance"):
                    self = super(Single, cls).__new__(cls, *args, **kwargs)
                    setattr(Single, "_instance", self)
        return getattr(Single, "_instance")


def func():
    print(Single())


if __name__ == '__main__':
    thread_list = list()
    for _ in range(1, 10):
        _ = threading.Thread(target=func)
        _.start()
        thread_list.append(_)

    for _ in thread_list:
        _.join()