multiprocessing for class method

Question

I want to use multiprocessing for a class method. I found out from this answer that Pool in multiprocessing cannot pickle class methods directly but there is a workaround for that by defining a function outside the class, and adds an additional argument(s) to that function (Similar suggestion is also on this blog). Hence, I tried to achieve that by the following simple program which has MyClass where I want to parallel fun. However, I am not getting any results (there is no bug). It seems I am missing something but I feel I am almost there! Any fix is really appreciated.

import multiprocessing
class MyClass:
 def __init__(self):
 pass
 def fun(self, myList):
 print myList
def unwrap_fun(obj, myList):
 return obj.fun(myList)
obj = MyClass()
mlp = multiprocessing.Pool(processes=multiprocessing.cpu_count())
mlp.imap_unordered(unwrap_fun, (obj, range(1, 10)))

Answer 1

You should call close() and join() from your main process. Try this:

import multiprocessing
class MyClass:
 def fun(self, myList):
 print myList
def unwrap_fun(myList):
 obj = MyClass()
 return obj.fun(myList)
if __name__ == '__main__':
 mlp = multiprocessing.Pool(processes=multiprocessing.cpu_count())
 mlp.imap_unordered(unwrap_fun, range(1, 10))
 mlp.close()
 mlp.join()