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单例模式

2018-06-18 00:24:12来源：未知阅读 ()

一、单例模式

单例模式分为四种：1.文件，2.类，3.基于__new__方法实现单例模式，4.基于metaclass方式实现

2.类实现如下：

class Sigletion(objects):
    import time
    def __init__(self):
        time.sleep(1)
    @classmethod
    def instance(cls,*args,**kwargs)
        if not hasattr(Sigletion,'_instance'):
            Sigletion._instance=Sigletion(*args,**kwargs)
        return Sigletion._instance

import threading

daf task(arg):
    obj=Sigletion.instance()
    print(obj)

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

类实现的-单例模式无法支持多线程的情况

import time
import threading
class Sigletion(object):
    _instance_lock=threading.Lock()
    def __init__(self):
        time.sleep(1)
    @classmethod
    def instance(cls,*args,**kwargs):
        if not hasattr(Sigletion,'_instance'):
            with Sigletion._instance_lock:
                if not hasattr(Sigletion,"_instace"):
                    Sigletion._instance=Sigletion(*args,**kwargs)
        return Sigletion._instance

def task(arg):
    obj=Sigletion.instance()
    print(obj)

for i in range(10):
    t=threading.Thread(target=task,args=[i,])
    t.start()
time.sleep(20)
obj=Sigletion.instance()
print(obj)

类实现的-单例模式无法支持多线程的情况

3.基于__new__方法实现单例模式

import time
import threading
class Singleton(object):
   _instance_lock=threading.Lock()
   def __init__(self):
       pass
   def __new__(cls, *args, **kwargs):
       if not hasattr(Singleton,"_instance"):
           with Singleton._instance_lock:
               if not hasattr(Singleton,"_instance"):
                   Singleton._instance=object.__new__(cls,*args,**kwargs)
       return Singleton._instance


obj1=Singleton()
obj2=Singleton()
print(obj1,obj2)

def task(arg):
    obj = Singleton()
    print(obj)

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

基于__new__方法实现的单例模式

4.基于metaclass方式实现单例模式

"""
1.对象是类创建，创建对象时候类的__init__方法自动执行，对象()执行类的 __call__ 方法
2.类是type创建，创建类时候type的__init__方法自动执行，类() 执行type的 __call__方法(类的__new__方法,类的__init__方法)

# 第0步: 执行type的 __init__ 方法【类是type的对象】
class Foo:
    def __init__(self):
        pass

    def __call__(self, *args, **kwargs):
        pass

# 第1步: 执行type的 __call__ 方法
#        1.1  调用 Foo类（是type的对象）的 __new__方法，用于创建对象。
#        1.2  调用 Foo类（是type的对象）的 __init__方法，用于对对象初始化。
obj = Foo()
# 第2步：执行Foodef __call__ 方法
obj()
"""

import threading

class SingletonType(type):
    _instace_lock=threading.Lock()
    def __call__(cls, *args, **kwargs):
        if not hasattr(cls, "_instance"):
            with SingletonType._instace_lock:
                if not hasattr(cls, "_instance"):
                    cls._instance = super(SingletonType,cls).__call__(*args, **kwargs)
        return cls._instance
class Foo(metaclass=SingletonType):
    def __init__(self,name):
        self.name=name


obj1 = Foo('name')
obj2 = Foo('name')
print(obj1,obj2)