Craig,
The short answer is. No threads may not be spawned. Use the datastore
to update/change status for the users. Only use memcache for reference
information or information which a invalid current status may be
acceptable. If the current status of a user must be valid, then the
datastore is the only way to persist the information.
Short reason for GAE thinking. The datastore handles replication
between all the servers automatically. The application servers are
load balanced and constantly in a state of flux. For example, server A
may answer the initial request by one user and Server B may answer the
request by the second user. Server A & B may actually be located in
separate data centers around the world.
Tim
On Nov 21, 2009, at 10:35 PM, Craig wrote:
> Hi,
>
> I have some questions regarding the limits of server code in GAE. Can
> I write server code that isn't tied to an http request - i.e. a thread
> that would always be running on the server and which servlets could
> communicate with? From what I've read it isn't possible but I just
> wanted to confirm.
>
> The application I'm writing is analogous to a chat system where 10
> users would log in and indicate their status (busy, idle, etc). I
> would prefer to be able to write a single server thread which would
> maintain this information and could give it to the individual servlets
> as needed. I.e. if I could write a persistent thread to manage this
> data I wouldn't need to deal with the data store, memcache, etc. I
> understand that this isn't possible - but please let me know if it is
> and what term I need to search for.
>
> Next, please let me know if the following architecture for my app
> makes sense. Since I cannot write a central thread to manage the
> information and respond to requests, I'll accomplish that using the
> memcache & data store. As users update their status the servlets will
> update the data. Then when the other clients refresh themselves, the
> servlets that they spawn will retrieve everyone's status from the data
> store and return it to the client. Does this structure make sense or
> am I missing something?
>
> (Eventually I'll use ServerPush to accomplish the refresh but I don't
> think that is relevant to the question).
>
> Thanks for your response and advice,
>
> Craig
>
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