【python】 多进程和单例模式

import threading
import time


class SingleTon(object):
    instance = None

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

    def __new__(cls, *args, **kwargs):
        if cls.instance:
            return cls.instance
        time.sleep(0.1)
        cls.instance = object.__new__(cls)
        return cls.instance


def task():
    obj = SingleTon('Arno')
    print(obj)


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

上述代码为单例模式和多进程的一个复合应用

但是 在执行时会出现异常情况

<__main__.SingleTon object at 0x0000018E3CEE13A0><__main__.SingleTon object at 0x0000018E3CEE1BE0>
<__main__.SingleTon object at 0x0000018E3D168490>
<__main__.SingleTon object at 0x0000018E3D168BE0><__main__.SingleTon object at 0x0000018E3D168490><__main__.SingleTon object at 0x0000018E3D168AF0>
<__main__.SingleTon object at 0x0000018E3D168970>

<__main__.SingleTon object at 0x0000018E3CEE1BE0>

<__main__.SingleTon object at 0x0000018E3D1689A0>
<__main__.SingleTon object at 0x0000018E3CEE13A0>

 我们没有得到想要的相同的内存地址的实例

因为 在10个线程同时走到time.sleep()时 会同时卡住 然后同时执行 

所以 我们加上一个锁就可以了

import threading
import time


class SingleTon(object):
    instance = None
    lock = threading.RLock()

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

    def __new__(cls, *args, **kwargs):
        with cls.lock:
            if cls.instance:
                return cls.instance
            time.sleep(0.1)
            cls.instance = object.__new__(cls)
            return cls.instance


def task():
    obj = SingleTon('Arno')
    print(obj)


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

 此时运行的结果为

<__main__.SingleTon object at 0x000001548D0E03A0>
<__main__.SingleTon object at 0x000001548D0E03A0>
<__main__.SingleTon object at 0x000001548D0E03A0>
<__main__.SingleTon object at 0x000001548D0E03A0>
<__main__.SingleTon object at 0x000001548D0E03A0>
<__main__.SingleTon object at 0x000001548D0E03A0>
<__main__.SingleTon object at 0x000001548D0E03A0>
<__main__.SingleTon object at 0x000001548D0E03A0>
<__main__.SingleTon object at 0x000001548D0E03A0>
<__main__.SingleTon object at 0x000001548D0E03A0>

均为同一内存地址