lesson06_callback.py

# SuperFastPython.com
# example of callback function for a one-off async task
from random import random
from time import sleep
from multiprocessing.pool import Pool

# custom function to be executed in a child process
def result_callback(return_value):
 # report a message
 print(f'Callback got: {return_value}', flush=True)

# task executed in a worker process
def task(identifier):
 # generate a value
 value = random()
 # report a message
 print(f'Task {identifier} executing with {value}',
 flush=True)
 # block for a moment
 sleep(value)
 # return the generated value
 return value

# protect the entry point
if __name__ == '__main__':
 # create and configure the multiprocessing pool
 with Pool() as pool:
 # issue tasks to the multiprocessing pool
 result = pool.apply_async(task, args=(0,),
 callback=result_callback)
 # close the multiprocessing pool
 pool.close()
 # wait for all tasks to complete
 pool.join()