#!/usr/bin/env python

"""
A simple example of parallel computation using a queue and the start method.
"""

import pprocess
import time
#import random

# Array size and a limit on the number of processes.

N = 10
limit = 10
delay = 1

# Work function.

def calculate(i, j):

    "A supposedly time-consuming calculation on 'i' and 'j'."

    #time.sleep(delay * random.random())
    time.sleep(delay)
    return (i, j, i * N + j)

# Main program.

if __name__ == "__main__":

    t = time.time()

    # Initialise the communications queue with a limit on the number of
    # channels/processes.

    queue = pprocess.Queue(limit=limit)

    # Initialise an array.

    results = [0] * N * N

    # Wrap the calculate function.

    calc = pprocess.MakeParallel(calculate)

    # Perform the work.

    for i in range(0, N):
        for j in range(0, N):
            queue.start(calc, *(i, j))

    # Store the results as they arrive.

    print "Finishing..."
    for i, j, result in queue:
        results[i*N+j] = result

    # Show the results.

    for i in range(0, N):
        for result in results[i*N:i*N+N]:
            print result,
        print

    print "Time taken:", time.time() - t

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