Python Multiprocessing Locks

Question

This multiprocessing code works as expected. It creates 4 Python processes, and uses them to print the numbers 0 through 39, with a delay after each print.

impor         


        

Answer 1

I think the reason is that the multiprocessing pool uses pickle to transfer objects between the processes. However, a Lock cannot be pickled:

>>> import multiprocessing
>>> import pickle
>>> lock = multiprocessing.Lock()
>>> lp = pickle.dumps(lock)
Traceback (most recent call last):
  File "", line 1, in 
    lp = pickle.dumps(lock)
...
RuntimeError: Lock objects should only be shared between processes through inheritance
>>> 

See the "Picklability" and "Better to inherit than pickle/unpickle" sections of https://docs.python.org/2/library/multiprocessing.html#all-platforms