Four-in-one singleton mode in Python

1 #Singleton mode: Unable to support multithreaded scenarios2 """3 class Singleton (object):4 def __init__ (self):5 Import Time6 time.sleep (1)7 @classmethod8 def instance (CLS, *args, **kwargs):9 if not hasattr (Singleton, "_instance"):Ten singleton._instance = Singleton (*args, **kwargs) One return singleton._instance A Import Threading -  - def task (ARG): the obj = singleton.instance () - print (obj) -  - For I in Range (Ten): + t = Threading. Thread (Target=task,args=[i,]) - T.start ()

First Kind

1 Import Time2 ImportThreading3 classSingleton (object):4_instance_lock =Threading. Lock ()5     def __init__(self):6Time.sleep (4)7 @classmethod8     defInstance (CLS, *args, * *Kwargs):9         if  notHasattr (Singleton,"_instance"):Ten With Singleton._instance_lock: One                 if  notHasattr (Singleton,"_instance"): ASingleton._instance = Singleton (*args, * *Kwargs) -         returnsingleton._instance - defTask (ARG): theobj =singleton.instance () -     Print(obj) -  forIinchRange (10): -t = Threading. Thread (target=task,args=[I,]) + T.start () -obj =singleton.instance () + Print(obj)

The second Kind

1 Import Time2 ImportThreading3 classSingleton (object):4_instance_lock =Threading. Lock ()5     def __init__(self):6         Pass7     def __new__(CLS, *args, * *Kwargs):8         if  notHasattr (Singleton,"_instance"):9 With Singleton._instance_lock:Ten                 if  notHasattr (Singleton,"_instance"): OneSingleton._instance = object.__new__(CLS, *args, * *Kwargs) A         returnsingleton._instance -Obj1 =Singleton () -Obj2 =Singleton () the Print(OBJ1,OBJ2)

Third Kind

1 ImportThreading2 classSingletontype (type):3_instance_lock =Threading. Lock ()4     def __call__(CLS, *args, * *Kwargs):5         if  notHasattr (CLS,"_instance"):6 With Singletontype._instance_lock:7                 if  notHasattr (CLS,"_instance"):8Cls._instance = Super (SINGLETONTYPE,CLS).__call__(*args, * *Kwargs)9         returncls._instanceTen classFoo (metaclass=singletontype): One     def __init__(self,name): ASelf.name =name -Obj1 = Foo ('name') -Obj2 = Foo ('name') the Print(OBJ1,OBJ2)

Fourth Type

Four-in-one singleton mode in Python