sigint handler

siginthandler.py

def graceful_cleanup(signum, frame):
    """
    signal handler function should perform all clean up tasks and optionall exit.
    I here it is just shutting down an executor which will exit the main loop, 
    i have also used it to set a flag so that processing in other threads will exit on the next test of that flag.
    The code below is unlikely to work as i was just using it in a test harness, but the signal module does work well for this 
    use case.
    """
    try:
        futurelist_lock.release()
    except RuntimeError as rte:
        print("Lock on futurelist is not set")
    print("Executing graceful shutdown")
    e.shutdown(wait=False)
    print("Have shutdown executor")
    for f in futurelist.keys():
        #if f.running():
        print(f"Cancelling thread {futurelist[f]}")
        print(f"{futurelist[f]} cancel operation returned:  {f.cancel()}")
        print(f"Cancelled status of {futurelist[f]} is {f.cancelled()}")

#
## main
# signal handler must be defined in main()
signal.signal(signal.SIGINT, graceful_cleanup)