#!/usr/bin/env python

"""

A simple example of parallel computation using message exchanges and the create

function.

NOTE: We could use the with statement in the innermost loop to package the

NOTE: try...finally functionality.

"""

import pprocess

import time

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

N = 10

limit = 10

delay = 1

# Monitoring class.

class MyExchange(pprocess.Exchange):

    "Parallel convenience class containing the array assignment operation."

    def store_data(self, ch):

        i, j, result = ch.receive()

        self.D[i*N+j] = result

# Main program.

if __name__ == "__main__":

    t = time.time()

    # Initialise the communications exchange with a limit on the number of

    # channels/processes.

    exchange = MyExchange(limit=limit)

    # Initialise an array - it is stored in the exchange to permit automatic

    # assignment of values as the data arrives.

    results = exchange.D = [0] * N * N

    # Perform the work.

    print "Calculating..."

    for i in range(0, N):

        for j in range(0, N):

            ch = exchange.create()

            if ch:

                try: # Calculation work.

                    time.sleep(delay)

                    ch.send((i, j, i * N + j))

                finally: # Important finalisation.

                    pprocess.exit(ch)

    # Wait for the results.

    print "Finishing..."

    exchange.finish()

    # 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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