Flask中的单例模式
1,基于文件的单例模式:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 | import pymysql import threading from DBUtils.PooledDB import PooledDB class SingletonDBPool( object ): _instance_lock = threading.Lock() def __init__( self ): self .pool = PooledDB( creator = pymysql, # 使用链接数据库的模块 maxconnections = 6 , # 连接池允许的最大连接数,0和None表示不限制连接数 mincached = 2 , # 初始化时,链接池中至少创建的空闲的链接,0表示不创建 maxcached = 5 , # 链接池中最多闲置的链接,0和None不限制 maxshared = 3 , # 链接池中最多共享的链接数量,0和None表示全部共享。PS: 无用,因为pymysql和MySQLdb等模块的 threadsafety都为1,所有值无论设置为多少,_maxcached永远为0,所以永远是所有链接都共享。 blocking = True , # 连接池中如果没有可用连接后,是否阻塞等待。True,等待;False,不等待然后报错 maxusage = None , # 一个链接最多被重复使用的次数,None表示无限制 setsession = [], # 开始会话前执行的命令列表。如:["set datestyle to ...", "set time zone ..."] ping = 0 , # ping MySQL服务端,检查是否服务可用。# 如:0 = None = never, 1 = default = whenever it is requested, 2 = when a cursor is created, 4 = when a query is executed, 7 = always host = '127.0.0.1' , port = 3306 , user = 'root' , password = '123456' , database = 'pooldb' , charset = 'utf8' ) def __new__( cls , * args, * * kwargs): if not hasattr (SingletonDBPool, "_instance" ): with SingletonDBPool._instance_lock: if not hasattr (SingletonDBPool, "_instance" ): SingletonDBPool._instance = object .__new__( cls , * args, * * kwargs) return SingletonDBPool._instance def connect( self ): return self .pool.connection() |
1 2 3 4 5 6 7 8 9 10 11 | from pool import SingletonDBPool def run(): pool = SingletonDBPool() con = pool.connect() # xxxxxx con.close() if __name__ = = '__main__' : run() |
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 | # 单例模式:无法支持多线程情况 """ class Singleton(object): def __init__(self): import time time.sleep(1) @classmethod def instance(cls, *args, **kwargs): if not hasattr(Singleton, "_instance"): Singleton._instance = Singleton(*args, **kwargs) return Singleton._instance import threading def task(arg): obj = Singleton.instance() print(obj) for i in range(10): t = threading.Thread(target=task,args=[i,]) t.start() """ # # 单例模式:支持多线程情况 """ 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 def task(arg): obj = Singleton.instance() print(obj) for i in range(10): t = threading.Thread(target=task,args=[i,]) t.start() time.sleep(20) obj = Singleton.instance() print(obj) """ |
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 | 基于__new__方法实现单例模式 # class Singleton(object): # def __init__(self): # print('init',self) # # # def __new__(cls, *args, **kwargs): # o = object.__new__(cls, *args, **kwargs) # print('new',o) # return o # # obj = Singleton() # # print('xxx',obj) 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() |
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 | 基于metaclass """ 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() """ """ class SingletonType(type): def __init__(self,*args,**kwargs): super(SingletonType,self).__init__(*args,**kwargs) def __call__(cls, *args, **kwargs): obj = cls.__new__(cls,*args, **kwargs) cls.__init__(obj,*args, **kwargs) # Foo.__init__(obj) return obj class Foo(metaclass=SingletonType): def __init__(self,name): self.name = name def __new__(cls, *args, **kwargs): return object.__new__(cls, *args, **kwargs) obj = Foo('name') """ 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) |
# ######################## 基于 类方法实现 ######################### """ 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 # 使用先说明,以后用单例模式,obj = Singleton.instance() # 示例: # obj1 = Singleton.instance() # obj2 = Singleton.instance() # print(obj1,obj2) # 错误示例 # obj1 = Singleton() # obj2 = Singleton() # print(obj1,obj2) """ # ######################### 基于__new__方式实现 ######################### """ 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 # 使用先说明,以后用单例模式,obj = Singleton() # 示例 # obj1 = Singleton() # obj2 = Singleton() # print(obj1,obj2) """ # ######################### 基于metaclass方式实现 ################### """ 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) """ # PS: 为了保证线程安全在内部加入锁
# 装饰器实现的单例模式 # def wrapper(cls): instance = {} def inner(*args,**kwargs): if cls not in instance: instance[cls] = cls(*args,**kwargs) return instance[cls] return inner @wrapper class Singleton(object): def __init__(self,name,age): self.name = name self.age = age obj1 = Singleton('haiyan',22) obj2 = Singleton('xx',22) print(obj1) print(obj2)
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