单例模式(Single Pattern)
Ensure a class has only one instancem, and provides a global point to access to it.



In [8]:

    
import threading
import time
class Singleton(object):
    def __new__(cls,*args,**kw):
        if not hasattr(cls,'_instance'):
            orig=super(Singleton,cls)
            cls._instance=orig.__new__(cls,*args,**kw)
        return cls._instance



In [6]:

    
class Bus(Singleton):
    lock=threading.RLock()
    def sendData(self,data):
        self.lock.acquire()
        time.sleep(3)
        print('Sending single data...',data)
        self.lock.release()

class VisitEntity(threading.Thread):
    my_bus=''
    name=''
    def getName(self):
        return name
    def setName(self,name):
        self.name=name
    def run(self):
        self.my_bus=Bus()
        self.my_bus.sendData(self.name)
for i in range(3):
    print('Entity %d begin to run...'%i)
    my_entity=VisitEntity()
    my_entity.setName('Entity_'+str(i))
    my_entity.start()









    



Entity 0 begin to run...
4533282352
Entity 1 begin to run...
4533282800
Entity 2 begin to run...
4533282632
Sending single data... Entity_0
Sending single data... Entity_1
Sending single data... Entity_2

advantage

Because of only one instance in global environment, it can save memory.
Because of the only one access point, it can be used to concurrent.
The only one Instace can store in memory, avoiding creating instance.

Disadvantage

Difficulty for expansion
revolt the Single Responsibilyt Principle
Unfriendly unit test



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