python单例模式处理多线程问题

# 单例模式处理多线程的问题
import threading
import time


class Single:
    instance = None

    def __init__(self, name):
        self.name = name

    def __new__(cls, *args, **kwargs):
        if not cls.instance:
            time.sleep(0.1)
            cls.instance = object.__new__(cls)
        return cls.instance


def dotask():
    obj = Single("test")
    print(obj)


for i in range(10):
    t = threading.Thread(target=dotask)
    t.start()
# 在使用多线程的情况下。输出id不同,说明此单例模式是存在问题的：
'''

<__main__.Single object at 0x000002C16CEA67C0><__main__.Single object at 0x000002C16CEA6850>
<__main__.Single object at 0x000002C16CEA1DC0>
<__main__.Single object at 0x000002C16CEA1640><__main__.Single object at 0x000002C16CEA1F10>
<__main__.Single object at 0x000002C16CEA18B0>
<__main__.Single object at 0x000002C16CEA1400>
<__main__.Single object at 0x000002C16CEA1670>

<__main__.Single object at 0x000002C16CEA1640>

<__main__.Single object at 0x000002C16CE9CF10>
'''
# 要解决多线程的单例模式，需要添加锁来处理
import threading
import time



class Single2:
    instance = None
    lock = threading.RLock()

    def __init__(self, name):
        self.name = name

    def __new__(cls, *args, **kwargs):
        with cls.lock:
            if not cls.instance:
                time.sleep(0.1)
                cls.instance = object.__new__(cls)
            return cls.instance


def dotask():
    obj = Single2("test")
    print(obj)


for i in range(10):
    t = threading.Thread(target=dotask)
    t.start()

# 此时输出就完全一致了：
'''
<__main__.Single2 object at 0x00000204B9A30C70><__main__.Single2 object at 0x00000204B9A30C70>

<__main__.Single2 object at 0x00000204B9A30C70>
<__main__.Single2 object at 0x00000204B9A30C70>
<__main__.Single2 object at 0x00000204B9A30C70>
<__main__.Single2 object at 0x00000204B9A30C70>
<__main__.Single2 object at 0x00000204B9A30C70>
<__main__.Single2 object at 0x00000204B9A30C70><__main__.Single2 object at 0x00000204B9A30C70><__main__.Single2 object at 0x00000204B9A30C70>

'''