How can I implement "real time" messaging on Google AppEngine?

Posted by Freed on Stack Overflow See other posts from Stack Overflow or by Freed
Published on 2010-04-17T22:31:39Z Indexed on 2010/04/17 22:33 UTC
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I'm creating a web application on Google AppEngine where I want the user to be notified a quickly as possible after certain events occour. The problem is similar to say a chat server in that I need something happening on one connection (someone is writing a message in a chat room) to propagate to a number of other connections (other people in that chat room gets the message). To get speedy updates from the server to the client I'm planning on using long polling with XmlHttpRequest, hoping that AppEngine won't interfere other than possibly restriing the timeout. The real problem however is efficient notification between connections on AppEngine.

Is there any support for this type of cross connection notification on AppEngine that does not involve busy-waiting? The only tools I can think of to do this at all is either using the data storage (slow) or memcache (unreliable), and none of them would let me avoid busy-waiting.

Note: I know about XMPP support on AppEngine. It's related, but I want a browser based solution, sending messages to the users by XMPP is not an option.

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