python使用装饰器实现单例模式

直接上代码：

第一种使用函数装饰器实现并且使用锁保证线程安全：

#不使用锁实现
def SingleInstance(cls):
    def new(cls,*args,**kwargs):
        if not  hasattr(cls,'instance'):
            cls.instance= object.__new__(cls)
        return cls.instance
    cls.__new__=new
    return cls

# 使用锁实现，确保线程安全
from multiprocessing import Lock

def SingleInstance(cls):
    cls.__lock__ = Lock()
    def new(cls,*args,**kwargs):
        cls.__lock__.acquire()
        try:
            if not  hasattr(cls,'instance'):
                cls.instance= object.__new__(cls)
            return cls.instance
        finally:
            cls.__lock__.release()
    cls.__new__=new
    return cls

#使用类实现
class SingleInstance:

    def __init__(self,lock=None):
        self.lock=lock or Lock()

    def __call__(self,cls):
        def new(cls, *args, **kwargs):
            self.lock.acquire()
            try:
                if not hasattr(cls, 'instance'):
                    cls.instance = object.__new__(cls)
                return cls.instance
            finally:
                self.lock.release()
        cls.__new__ = new
        return cls

使用方法   @SingleInstance

@SingleInstance
class A:
    pass

第二种使用类实现装饰器：

class SingleInstance:
    def __init__(self,*args,**kwargs):
        self.arg=args
        self.kwargs=kwargs

    def __call__(self, cls):
        def new(cls):
            if not hasattr(cls, 'instance'):
                cls.instance = object.__new__(cls)
            return cls.instance

        cls.__new__ = new
        return cls

使用方法    @SingleInstance(*args,**kwargs)

@SingleInstance(*args,**kwargs)
class A:
    pass

第三种使用元类实现装饰器：

class Meta(type):
    def __call__(self, cls, *args, **kwargs):
        def new(cls, *args, **kwargs):
            if not hasattr(cls, 'instance'):
                cls.instance = object.__new__(cls)
            return cls.instance

        cls.__new__ = new
        return cls

class SingleInstance(metaclass=Meta):
    pass


使用方法    @SingleInstance

@SingleInstance
class A:
    pass