Add timeout to composite calcs

[Randle Taylor]

It is currently possible for a composite calculation to run forever and effectively cause a denial of service attack type situation.

While this is unlikely to happen in practice it would be a good idea to add a timeout to composite calcs either using a separate thread or signals.

[Randle Taylor]

Example timeout using multiprocessing

[Randle Taylor]

This is not quite as straightforward as I hoped. Going to put this on hold for now.