实现单例模式的方式2

方式一: 能保证线程安全

定义类的时候实现单例模式

import time
import threading
class Singleton(object):
    _instance_lock = threading.Lock()

    def __init__(self):
        time.sleep(1)   # 这里添加耗时操作,是演示不加线程锁的情况下,会出现创建多个实例的情况

    @classmethod
    def instance(cls, *args, **kwargs):
        with Singleton._instance_lock:
            if not hasattr(Singleton, "_instance"):
                Singleton._instance = Singleton(*args, **kwargs)
        return Singleton._instance


def task():
    obj = Singleton.instance()
    print(id(obj))
list1 = list()
for i in range(10):
    t = threading.Thread(target=task)
    t.start()
    list1.append(t)
for i in list1:
    i.join()
obj = Singleton.instance()
print(obj)

方式二: 能保证线程安全

对已定义好的类实现单例模式

# 装饰器的方法实现类的单例模式
from functools import wraps
import threading

global_lock = threading.Lock() # 制定一个全局锁
def sington(cls):
    _instances = {}
    @wraps(cls)
    def wrapper(*args,**kwargs):
        with global_lock:
            if cls not in _instances:
                _instances[cls] = cls(*args,**kwargs)
        return _instances[cls]

    return wrapper


@sington
class Test:
    def __init__(self,*args,**kwargs):
        pass


test1 = Test()
test2 = Test()
print(id(test1) == id(test2))  # True