一. 单例模式四种方式
用于mysql连接时,防止每次操作都去创建一个数据库连接,使用单例模式仅在第一次创建连接,以后均使用该连接即可。
1. 文件导入
2. 基于类
无法支持多线程
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import threading class Singleton(object): def __init__(self): pass @classmethod def instance(cls, *args, **kwargs): if not hasattr(Singleton, "_instance"): Singleton._instance = Singleton(*args, **kwargs) return Singleton._instance obj = Singleton.instance()
支持多线程
![](https://images.cnblogs.com/OutliningIndicators/ContractedBlock.gif)
import time import threading class Singleton(object): _instance_lock = threading.Lock() def __init__(self): time.sleep(1) @classmethod def instance(cls, *args, **kwargs): if not hasattr(Singleton, "_instance"): with Singleton._instance_lock: if not hasattr(Singleton, "_instance"): Singleton._instance = Singleton(*args, **kwargs) return Singleton._instance # 第一次调用 def task(arg): obj = Singleton.instance() print(obj) for i in range(10): t = threading.Thread(target=task,args=[i,]) t.start() # 第二次调用 time.sleep(20) obj = Singleton.instance()
3. 使用__new__
无法支持多线程
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class Singleton(object): def __init__(self,name): self.name = name def __new__(cls, *args, **kwargs): if not hasattr(Singleton, "instance"): Singleton.instance = object.__new__(cls) return Singleton.instance obj = Singleton("alex") obj1 = Singleton("alex") obj2 = Singleton("alex")
支持多线程
![](https://images.cnblogs.com/OutliningIndicators/ContractedBlock.gif)
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) return Singleton.instance return Singleton.instance def task(): obj = Singleton() print(obj) for i in range(5): t = threading.Thread(target=task) t.start()
4. 基于metaclass
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-------------------------------(一)------------------------------- # 创建对象 class SingletonType(type): def __call__(cls, *args, **kwargs): obj = super(SingletonType,cls).__call__(*args, **kwargs) #type类帮创建__new__和__init__并返回 return obj class Foo(metaclass=SingletonType): def __init__(self,name): self.name = name obj = Foo("alex") -------------------------------(二)------------------------------- import threading class SingletonType(type): _instance_lock = threading.Lock() def __call__(cls, *args, **kwargs): if not hasattr(cls, "_instance"): with SingletonType._instance_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)