David, I would suggest using a Request Repeater pattern rather than
Task Queues. What you want to achieve might be difficult or impossible
with Task Queues.
Rather, You can have a request handler, say /processevent, that grabs
an event record from the data store table that holds them, processes
the event and then uses URLFetch to call itself. That gives you single
threadedness.
You can use the event model's __key__ to find the correct event. If
you select 1 record and order on __key__, you'll get the one with the
lowest key, and by definition, that should be the oldest record in the
entity group.
On Aug 3, 6:05 am, David Given wrote:
> Hi,
>
> I'm trying to write a game using AppEngine. As a result, I need some
> mechanism for running the game AI.
>
> I've considered various architectures and the approach that seems the
> most workable is to have, in the datastore, a priority queue of events
> based on timestamp. I post events to the queue, and then process them in
> order whenever it's necessary to update the state of the game world.
> Most of this isn't hard.
>
> The problem is that I can't find any way of achieving the 'in order'
> part of the problem. It's vitally important that the event processing
> happens serially, or else I'll end up processing events out of order,
> with hilarious consequences --- I would like my unit to pick up cargo
> *before* it departs the current location, thanks very much!
>
> Normally I'd achieve this by having a single thread do all the AI
> processing, so the AI becomes intrinsically serialised. Naturally, this
> isn't possible in AppEngine. The only other approach I can think of is
> to put some kind of big lock around the AI processing routine, to ensure
> that only one thread at a time handles events; but AppEngine doesn't
> have that kind of lock. Transactions aren't suitable because they're not
> blocking.
>
> This must be a situation people have encountered before --- any
> suggestions as to the best way to achieve this sort of thing?
>
> --
> David Given
> d...@cowlark.com
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