Example use of concurrent.futures

concurrent_futures_example.py

#!/usr/bin/env python

"""
Example of how to use futures with ProcessPoolExecutor or ThreadPoolExecutor.
"""

from concurrent import futures

def long_running_function():
    """
    Runs for 10 seconds and returns the current time when complete.
    """
    import time
    time.sleep(10)
    return "current time.time(): %s" % time.time()

def all_done(future):
    """
    Prints `future.result()` (what was returned by the future).
    """
    print("All done!  Result: '%s'" % future.result())

if __name__ == "__main__":
    print("Creating a ProcessPoolExecutor...")
    executor = futures.ProcessPoolExecutor() # max_workers == number of cores by default
    #executor = futures.ThreadPoolExecutor(max_workers=4) # Threaded way
    print("Submitting our long-running function to the executor...")
    future = executor.submit(long_running_function)
    print("Adding a callback that will be called when that function completes...")
    future.add_done_callback(all_done)
    # You could proceed with more code at this point but because this is the
    # last thing in our little script here it will automatically block until
    # the last executor submission is complete.
    # If you want to wait for multiple futures to complete you could use:
    #   futures.wait(list_of_futures, timeout=30)