import threading

import time

class Singleton(object):

_instance_lock = threading.Lock()

def __init__(self, cls):

self._cls = cls

self._instance = {}

# def __call__(self, *args, **kwargs):

# if self._cls not in self._instance:

# time.sleep(1)

# self._instance_lock.acquire()

# try:

# if self._cls not in self._instance:

# self._instance[self._cls] = self._cls(*args, **kwargs)

# finally:

# self._instance_lock.release()

# return self._instance[self._cls]

def __call__(self, *args, **kwargs):

if self._cls not in self._instance:

time.sleep(1)

with self._instance_lock:

time.sleep(1)

if self._cls not in self._instance:

time.sleep(1)

self._instance[self._cls] = self._cls(*args, **kwargs)

return self._instance[self._cls]

@Singleton

class A(object):

a = 1

def __init__(self, x=0):

self.x = x

def task(arg):

obj = A(arg)

print(id(obj))

for i in range(10):

t = threading.Thread(target=task,args=[i,])

t.start()