# pp-web / pp_examples / callback.py

 ``` 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99``` ```#!/usr/bin/env python # File: callback.py # Author: Vitalii Vanovschi # Desc: This program demonstrates parallel computations with pp module # using callbacks (available since pp 1.3). # Program calculates the partial sum 1-1/2+1/3-1/4+1/5-1/6+... # (in the limit it is ln(2)) # Parallel Python Software: http://www.parallelpython.com import math import time import thread import sys import pp class Sum(object): """Class for callbacks """ def __init__(self): self.value = 0.0 self.lock = thread.allocate_lock() self.count = 0 def add(self, value): """ the callback function """ # we must use lock here because += is not atomic self.count += 1 self.lock.acquire() self.value += value self.lock.release() def part_sum(start, end): """Calculates partial sum""" sum = 0 for x in xrange(start, end): if x % 2 == 0: sum -= 1.0 / x else: sum += 1.0 / x return sum print """Usage: python callback.py [ncpus] [ncpus] - the number of workers to run in parallel, if omitted it will be set to the number of processors in the system """ start = 1 end = 20000000 # Divide the task into 128 subtasks parts = 128 step = (end - start) / parts + 1 # tuple of all parallel python servers to connect with #ppservers = ("*",) # auto-discover #ppservers = ("10.0.0.1","10.0.0.2") # list of static IPs ppservers = () if len(sys.argv) > 1: ncpus = int(sys.argv[1]) # Creates jobserver with ncpus workers job_server = pp.Server(ncpus, ppservers=ppservers) else: # Creates jobserver with automatically detected number of workers job_server = pp.Server(ppservers=ppservers) print "Starting pp with", job_server.get_ncpus(), "workers" # Create anm instance of callback class sum = Sum() # Execute the same task with different number # of active workers and measure the time start_time = time.time() for index in xrange(parts): starti = start+index*step endi = min(start+(index+1)*step, end) # Submit a job which will calculate partial sum # part_sum - the function # (starti, endi) - tuple with arguments for part_sum # callback=sum.add - callback function job_server.submit(part_sum, (starti, endi), callback=sum.add) #wait for jobs in all groups to finish job_server.wait() # Print the partial sum print "Partial sum is", sum.value, "| diff =", math.log(2) - sum.value job_server.print_stats() # Parallel Python Software: http://www.parallelpython.com ```