Python multiprocessing example

python-multiprocessing.py

import multiprocessing as mp
import time

result_list_pool = []
result_list_process = []


def foo_pool(x):
    time.sleep(2)
    return x*x


def foo_pool_p(x, conn):
    time.sleep(2)
    conn.send(x*x)
    conn.close


def log_result(result):
    # This is called whenever foo_pool(i) returns a result.
    # result_list is modified only by the main process, not the pool workers.
    result_list_pool.append(result)


def apply_async_with_callback():
    pool = mp.Pool()
    print("  pool with with {} processes".format(pool._processes))
    for i in range(8):
        pool.apply_async(foo_pool, args=(i, ), callback=log_result)
    pool.close()
    pool.join()
    print(result_list_pool)


def paralell_process():
    # create a list to keep all processes
    processes = []
    # create a list to keep connections
    parent_connections = []

    # create 8 processes
    for i in range(8):
        # create a pipe for communication
        parent_conn, child_conn = mp.Pipe()
        parent_connections.append(parent_conn)

        # create the process, pass arg and connection
        process = mp.Process(target=foo_pool_p, args=(i, child_conn,))
        processes.append(process)

    # start all processes
    for process in processes:
        process.start()

     # make sure that all processes have finished
    for process in processes:
        process.join()

    # collect result from processes
    count = 0
    for parent_connection in parent_connections:
        value = parent_connection.recv()
        result_list_process.append(value)

    print(result_list_process)


if __name__ == '__main__':
    print("running with pool.apply_async")
    start = time.perf_counter()
    apply_async_with_callback()
    end = time.perf_counter()
    print("time: ", round(end-start, 2))

    print("-----------------------------------------------------")

    print("running with Process")
    start = time.perf_counter()
    paralell_process()
    end = time.perf_counter()
    print("time: ", round(end-start, 2))