How can processes share list between each other in

Question

Please be so kind to point me on how can a list or an array be shared between processes so they can access/append/delete data from it? Do i need to use Manager for it? For example i have code that pings several hosts using multiprocessing:

#!/usr/bin/env python

from multiprocessing import Pool
import os

def ping(ip):
  report = ("No response","Partial Response","Alive")
  pingaling = os.popen("ping -q -c2 "+str(ip),"r")
  while 1:
    line = pingaling.readline()
    try:
      result = line[line.find(','):].split()[1]
      output = report[int(result[0])]
    except:
      pass
    if not line: break
  print "Testing %s : %s!" % (ip, output)

if __name__ == '__main__':
  pool = Pool(processes=3)
  host = ['81.24.212.'+str(x) for x in range(10)]
  pool.map(ping, host, 1)
  pool.close()
  pool.join() 

But the output is unsorted, however i want to add output to an array and sort it:

Testing 81.24.212.1 : Alive!
Testing 81.24.212.2 : Alive!
Testing 81.24.212.6 : Alive!
Testing 81.24.212.0 : No response!
Testing 81.24.212.5 : No response!
Testing 81.24.212.3 : No response!
Testing 81.24.212.4 : No response!
Testing 81.24.212.9 : No response!
Testing 81.24.212.7 : No response!
Testing 81.24.212.8 : No response!

Answer 1

note that pool.map acts a lot like the buildin map function and like it returns a list of the results of the application of the given function to elements in the given list.

so you need only have ping() return what it found and then do:

list_of_values = pool.map(ping, host, 1)

after which you can use the list_of_values any way you like

Answer 2

The data structure you're looking for is multiprocessing.Queue. You can pop values out of the queue into a list until you've got as many values as there were processes, then sort and print them. With your particular application, however, Dan D's pool.map answer has a better approach.

Answer 3

I strongly recommend that you use something like redis ( http://redis.io ), which is a datastructures server - it exists to facilitate the sharing of datastructures in a robust manner.