How does Python 3 multiprocessing Pool know when to pick another set of values? -

i have own package , want paralelize tasks doing. need open session, execute query , close session in single worker. having example multiprocessing documentation, script looks this:

from multiprocessing import pool owndb import odb  def worker(y):     session = odb('db_name', 'user', 'password')     print(session)     result = session.query("select name table")     session.disconnect()     return [y, result]  if __name__ == '__main__':     test_nums = [1,2,3,4,5,6]     pool(processes=2) p:         print(p.map(worker, test_nums)) 

this code, without openning , closing session works expected. when execute session code, results first set of pool workers (in case 2) , runs till kill it.

my assumption multiprocessing package not know when worker done - why be? how worker indicates finished?