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I have a question about python's multiprocessing module, when I'm trying to find a pin why is 1 process faster than 10 or 15 processes, I thought the more processes you got running the faster you will get your results, but for some reason that's not the case can someone example why the script takes a longer time when the for loop number is greater than 1. # - Code 1 #!/usr/bin/env python # # # from multiprocessing import Process from random import choice from subprocess import * from time import sleep

def PinGuess(pin,nums):
  global Found,Invalid
  while not Found:
    Numbers = xrange(nums)
    current_pin = int(choice(Numbers))
    if current_pin not in Invalid:
     call(['clear'])
     print 'Trying: {}'.format(current_pin)
     if current_pin == pin: Found = True
     else: Invalid.append(current_pin)


  print len(Invalid)

if __name__ == '__main__':
  Found = False
  Invalid = []
  Pin = 123

  for i in range(1):
   Process(target=PinGuess, args=(Pin,300)).start()

# - Output 1
Trying: 123
104
real    0m0.904s
user     0m0.316s
sys     0m0.440s

# - Code 2
#!/usr/bin/env python
#
#
#
from multiprocessing import Process
from random import choice
from subprocess import *
from time import sleep


def PinGuess(pin,nums):
  global Found,Invalid
  while not Found:
    Numbers = xrange(nums)
    current_pin = int(choice(Numbers))
    if current_pin not in Invalid:
     call(['clear'])
     print 'Trying: {}'.format(current_pin)
     if current_pin == pin: Found = True
     else: Invalid.append(current_pin)


  print len(Invalid)

if __name__ == '__main__':
  Found = False
  Invalid = []
  Pin = 123

  for i in range(10):
   Process(target=PinGuess, args=(Pin,300)).start()

# - Output 2
Trying: 123
296
real    0m10.530s
user    0m3.652s
sys     0m8.328s
user5117999
  • 49
  • 5
  • Possible duplicate of [testing python multiprocessing: low speed because of overhead?](http://stackoverflow.com/questions/26630245/testing-python-multiprocessing-low-speed-because-of-overhead) – paisanco Oct 16 '16 at 16:10
  • but you're running 10 processes on a 300 range vs 1 process on a 300 range: you're just wasting CPU power here. – Jean-François Fabre Oct 16 '16 at 16:11

0 Answers0