Modeling a shared sense of time

[nigelkerr]

I would like to model a business model we are considering getting into with P. An important concept to the model is the current date: the dates items were published in the past, when a given actor's subscriptions start or end, what is in subscriptions on a given date, whether something is true on a specific date.

Do folks have ways that they have modeled this kind of time in P?

Some ideas I've had:

• Model the Calendar in the universe, and somehow make sure all message exchanges for a given date all finish before the calendar increments the day forward. We've made all the progress on this day that we need to, so go ahead and roll over to the next day. A lot of detailed work and stored state to get this to happen, it seems.
• Model the Calendar in the universe, but all it is doing is broadcasting a date-switch periodically, we don't try to manage all the progress. Transacting business takes as long as it has to take, but if the dates increment while something is still rattling through, that work is just "delayed" into the next day. That "periodically" accomplished by some dumb contrivance of the Calendar sending itself a bunch of countdown messages. Straightforward if unreliable, since any machine can pick up events whenever, the Calendar could burn through its countdown.

It is entirely possible that I should be modeling somewhere other than P for this kind of case, and that's cool, too. Any ideas appreciated. Thank you.