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单例模式在类中实现装饰器批量装饰实现单例模式 #xff0c;且不丢失类型提示限制实例个数 1.重写__new__方法实现多线程情况下的单例模式
用new方法实现单例模式
import time, threadingclass Singleton:单例模式————最多只允许创…目录
单例模式在类中实现装饰器批量装饰实现单例模式 且不丢失类型提示限制实例个数 1.重写__new__方法实现多线程情况下的单例模式
用new方法实现单例模式
import time, threadingclass Singleton:单例模式————最多只允许创建一个该类实例_lock threading.Lock()_instance Nonedef __new__(cls, a, b, *args, **kwargs):time.sleep(1) # 模拟高并发情况with cls._lock:# print(进入lock区域)if not cls._instance:cls._instance object.__new__(cls)# cls._instance super().__new__(cls) # 与上一条作用相同# cls._instance.a areturn cls._instance# S Singleton(1, 2)
# print(S)def task(a, b):s Singleton(a, b)print(s)for i in range(5):t threading.Thread(targettask, args(2, 3))t.start()运行始终为单一实例
__main__.Singleton object at 0x0000029E71D3B070__main__.Singleton object at 0x0000029E71D3B070
__main__.Singleton object at 0x0000029E71D3B070__main__.Singleton object at 0x0000029E71D3B070__main__.Singleton object at 0x0000029E71D3B0702.使用装饰器实现多线程情况下的单例模式
想要批量给多个类实现单例模式自然少不了装饰类的装饰器 先介绍第一种方法线程锁的方式和前面的稍有不一样没有使用类的内部属性记录实例对象而是使用了字典键唯一的特性将类对象Example作为键实例化后的对象作为值
2.1 第一种实现方式不推荐使用 错误示例
import time
from functools import wraps
import threadingdef singleton_dec(class_):map_ {} # 定义一个字典类本身作为键实例化后的对象作为其相应的值wraps(class_) # 顺便复习一下装饰器将被装饰的函数改回原来的属性和名字def singleton(*args):# print(class_.__name__)# print(class_.foo.__name__)if class_ not in map_: # 如果类没有在字典就实例化time.sleep(1) # 没有加锁的情况下模拟多线程的情况map_[class_] class_(*args) # 实例化类方法并存到字典中return map_[class_] # 字典中有这个类就不实例化return singletonsingleton_dec
class EXAMPLE:def __init__(self, paramabc):self.param paramdef foo(self):pass# E1 EXAMPLE(123)
# print(E1.param)
# print(E1)
# E2 EXAMPLE(456) # 由于EXAMPLE已经实例化了在map_中这一步并没有对EXAMPLE做出任何改变
# print(E2.param) # 输出的依然是123
# print(E2)def task():e EXAMPLE()print(e)for i in range(5):t threading.Thread(targettask)t.start()加上sleep模拟多线程的执行结果
__main__.EXAMPLE object at 0x000001BD894A7128
__main__.EXAMPLE object at 0x000001BD8949E710
__main__.EXAMPLE object at 0x000001BD894A1DD8
__main__.EXAMPLE object at 0x000001BD8949EB00
__main__.EXAMPLE object at 0x000001BD8949E710可以看到在并发情况很高的时候并没有实现单例化
因为方法二没有像方法一一样设置线程锁所以这里会出现创建多个实例的情况
想要实现单例也需要像方法一中一样加上线程锁
不过是给字典方法加上一个线程锁 示例
# -*- coding: utf-8 -*-
import threading, time
from functools import wrapsclass DictWithLock(dict):lock threading.Lock()def __init__(self, *args, **kwargs):super().__init__(*args, **kwargs)def singleton_decorator(callable_obj):dl DictWithLock()wraps(callable_obj)def inner(*args, **kwargs):# print(测试, *args, **kwargs)time.sleep(1)with dl.lock: # 一次只能有一个线程使用DictWithLock的lock属性# print(进入lock区域)if not dl.get(_instance):dl[_instance] callable_obj(*args, **kwargs)return dl[_instance]return innersingleton_decorator
class Test:def __init__(self, a0, b1):print(Test.test, a, b)def task(a, b):t Test(a, b)print(t) # t.a时不会有提示# t0 Test(2, 3)
# print(t0)for i in range(5):tsk threading.Thread(targettask, args(2, 3))tsk.start()输出结果
Test.test 2 3
__main__.Test object at 0x00000292250AB070
__main__.Test object at 0x00000292250AB070__main__.Test object at 0x00000292250AB070__main__.Test object at 0x00000292250AB070__main__.Test object at 0x00000292250AB070已结束退出代码 0
线程各自异步执行但始终只会创建一个Example的实例
这种方式是按照一般实现装饰器的方式实现不过这种装饰器有明显的缺点被装饰过的类不会有类型提示 于是祭出第二种类的装饰器写法 2.2 第二种实现方式 被装饰过的类不会丢失类型提示
# -*- coding: utf-8 -*-
import threadingdef Singleton(cls):# print(log singleton)cls._instance Nonecls._lock threading.Lock()def __new__(*args, **kwargs): # print(flog new, args, kwargs) # 实际上args中也包含cls和相关的参数with cls._lock:if not cls._instance:cls._instance object.__new__(cls)return cls._instancecls.__new__ __new__return clsSingleton
class T:def __init__(self, a):self.a adef t1():t T(1)tt T(2)print(t, t.a) # t.a时有提示print(tt, t.a)def t11():def task(a):s T(a)print(s)for i in range(5):t threading.Thread(targettask, args(2, ))t.start()if __name__ __main__:# t1()t11()
输出
__main__.T object at 0x000001EFE5977850
__main__.T object at 0x000001EFE5977850
__main__.T object at 0x000001EFE5977850
__main__.T object at 0x000001EFE5977850
__main__.T object at 0x000001EFE5977850限制实例个数的模式————limit实例模式
__new__()方法实现最多创建3个实例的模式
class LimitedInstances:限制实例个数的模式————limit实例模式_instances []limit 3def __new__(cls, *args, **kwargs):if not len(cls._instances) cls.limit: # 若个数达到limit说明已满raise Exception(fCan not create instance more than {cls.limit}.)instance super().__new__(cls)cls._instances.append(instance)return instancedef __delete__(self):self._instances.remove(self)LI1 LimitedInstances(1, 2)
LI2 LimitedInstances(2, 2)LI3 LimitedInstances(3, 2)
LI3.__delete__()
LI4 LimitedInstances(4, 2)
print(f删除一个又加进来一个还是3个\n, LimitedInstances._instances)
# LI5 LimitedInstances(5, 2) # 超过3个会报错运行结果限制最多3个实例
删除一个又加进来一个还是3个实例[__main__.LimitedInstances object at 0x00000278A03BDE20, __main__.LimitedInstances object at 0x00000278A03BDDC0, __main__.LimitedInstances object at 0x00000278A03BD520]模拟高并发情况下还是可能会出现超过3个实例的情况
import time, threadingclass LimitedInstances:限制实例个数的模式————limit实例模式_instances []limit 3def __new__(cls, *args, **kwargs):if not len(cls._instances) cls.limit: # 若个数达到limit说明已满raise Exception(fCan not create instance more than {cls.limit}.)instance super().__new__(cls)time.sleep(1) # 模拟高并发情况cls._instances.append(instance)return instancedef __delete__(self):self._instances.remove(self)def task():LI LimitedInstances()print(LI)def task():LI LimitedInstances()print(LI)for i in range(6):t threading.Thread(targettask, args())t.start()
time.sleep(2)
print(len(LimitedInstances._instances), LimitedInstances._instances)运行结果出现了6个不同的实例的情况
__main__.LimitedInstances object at 0x0000027066EC8DF0__main__.LimitedInstances object at 0x0000027066EED370__main__.LimitedInstances object at 0x0000027066EC8BB0
__main__.LimitedInstances object at 0x0000027066EED0D0
__main__.LimitedInstances object at 0x0000027066EC8610
__main__.LimitedInstances object at 0x0000027066EED610
6 [__main__.LimitedInstances object at 0x0000027066EC8DF0, __main__.LimitedInstances object at 0x0000027066EED370, __main__.LimitedInstances object at 0x0000027066EC8BB0, __main__.LimitedInstances object at 0x0000027066EED0D0, __main__.LimitedInstances object at 0x0000027066EC8610, __main__.LimitedInstances object at 0x0000027066EED610]解决方式同之前加上线程锁
import time, threadingclass LimitedInstances:限制实例个数的模式————limit实例模式_instances []limit 3_lock threading.Lock()def __new__(cls, *args, **kwargs):with cls._lock: # 一次只能一个线程执行实例个数判断和实例存入if not len(cls._instances) cls.limit: # 若个数达到limit说明已满raise Exception(fCan not create instance more than {cls.limit}.)instance super().__new__(cls)time.sleep(1) # 模拟高并发情况cls._instances.append(instance)return instancedef __delete__(self):self._instances.remove(self)def task():LI LimitedInstances()print(LI)for i in range(6):t threading.Thread(targettask, args())t.start()
# time.sleep(2)
# print(len(LimitedInstances._instances), LimitedInstances._instances)
运行时创建超过了3个实例会报错
