What's the best way to coordinate javascript clients to a single backend game?

Question

What's the best method to use to notify javascript client's of changes that occur in a game asynchronously (i.e. moves made by other clients). As an example, assume a turn based board game. Should I just have the client poll the PHP backend every second or so for new moves, or is there a better way to send an asynchronous notification to the other clients in the same game? What is your best idea for how to distribute the notification between the backend instances for each client?

I'm currently planning on putting each move in an SQL database and then having each client poll the database for new moves every second, but this seems kludgy and inefficient...

Answer 1

Polling every second or so is one option, but you may want to consider long polling instead, to reduce the latency.

Quoting Comet Daily: The Long-Polling Technique:

The long-polling Comet technique is a technique that optimizes traditional polling to reduce latency.

Traditional polling sends an XMLHttpRequest to the server in fixed intervals. For example, open a new XMLHttpRequest every 15 seconds, receive an immediate response, and close the connection.

Long-polling sends a request to the server, but a response is not returned to the client until one is available. As soon as the connection is closed, either due to a response being received by the client or if a request times out, a new connection is initiated. The result is a significant reduction in latency because the server usually has a connection established when it is ready to return information to return to the client.

Answer 2

Unfortunately there are only a few options for this. All will involve having some sort of client on the server sending down notifications if you want to use push technology. Or else polling is the way to go.

But just as a tangent here is a solution I played with years ago: http://www.spsolutionscorp.com/blog/2007/03/14/RealTimeUpdatesToWebPageUsingMacromediaFlash.aspx

The gist of it was this: Sql Server with service broker turned on. .Net service on server that is using SqlDependency to listen for changes to query result (http://support.microsoft.com/kb/555893). Once change occurred the .net service looped through all connections that had been made from a flash client that I wrote about in the above blog article. Then the flash app could call out to the javascript on the page.

It was a crazy idea and I never put into productions. But depending on your use it might be worth looking into and it was pretty easy to get going.

But again this was a totally crazy idea and again one I never put into production so use at your own risk. Just thought I would share.

Answer 3

Polling can easily stack up and consume a lot of resources (eg: bandwidth), no matter how lightweight your requests and responses are.

http://ajaxpatterns.org/Periodic_Refresh

You might want to try and use Comet/HTTP Streaming http://ajaxpatterns.org/HTTP_Streaming