Here is the first version i found and think is good : LINK
As you will see there is some time and sleep things in it , i put em there to test what happens when some threaded classes use it. And as you may imagine some of the threads got different references of that Class. Here is the Thread i used :
from threading import *
import time
import thread
class ThreadSingleton(Thread):
"""
A simple thread to work on that
"""
def __init__(self,id):
Thread.__init__(self)
self.id = id
def run(self):
"""
Here initialize the singleton
"""
self.s=Singleton()
print "Im thread %d and %d"%(self.id,id(self.s))
time.sleep(2)
def get_singleton(self):
return id(self.s)
Here is the code that tests it :
def singleton(t="threaded"):
for j in range(100):
threads = []
for i in range(10):
if t!="threaded":
threads.append(ThreadSingleton(i))
else:
threads.append(RealThreadedSingleton(i))
for i in threads:
i.start()
for i in threads:
i.join()
print "The final ids are :"
t0 = threads[0]
for i in threads:
assert t0.get_singleton() == i.get_singleton()
t0.s.destroy()
if j%10 == 0:
print "************** %d COMPLETED **********"%j
After those tests i got some Assertion Errors because some of the threads got different references of the object. What we know from here is that our Singleton is not thread-safe and we should fix it. Here is the threaded version of the Singleton LINK :
To test that new verison i nedded some new ThreadClass to call the new created Singleton :
class RealThreadedSingleton(ThreadSingleton):
def run(self):
"""
Here initialize the singleton
"""
self.s=ThSingleton()
print "Im thread %d and %d"%(self.id,id(self.s))
time.sleep(2)
After final changes i run the tests 1000 times and didnt have any problems. Why we should bother to have Singleton threa-safe , because i'm going to use it in some frameworks that uses threads heavily, so icant be sure when that one will be called. To conclude, when write some cool classes always should think the posibility of theraded usages.
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