Re: How to emulate queue for CGI script?

I'd put the logic in the browser. You're already using Ajax, so Javascript is already enabled. It could go something like this.

The user composes a request (webform?) and sends it to your server by Ajax.
Your CGI script check how long it has been since a request has been sent to a particular server. If it's been less than 10 seconds (or there are other people in the queue) give back a negative response to the browser via the Ajax response, together with an estimate of how much time it should wait before retrying.
You might also keep a queue for each server, and pass back the queue position to the user, but you'd have to take into account that some users will not wait, so the queue might actually move faster than the first estimate. I'd have the server wait up to 2 seconds for a retry by the user, before moving on to the next person in the queue.
The browser can then alert the user of the wait time, wait for the indicated time, and try again (with window.setTimeout).
If the person is the first in the queue, service the request and return a positive answer.

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Re^2: How to emulate queue for CGI script? by thargas (Deacon) on Mar 21, 2011 at 15:04 UTC
There is a problem with trying to do the rate-limiting in the browser: if there is more than one client, you'll blow the limit. I think it has to be done in the back-end. You ought to be able to get the effect you want by using CPAN modules. You may be able to simply use HTTP::Cache::Transparent.	[reply]
Re^3: How to emulate queue for CGI script? by Limbic~Region (Chancellor) on Mar 21, 2011 at 17:18 UTC
thargas, Perhaps you missed where the CGI checks how long it has been since a request was made? That will be for all clients. The trouble I see with it is a race condition where two clients check at the same time and both think it is ok. One actually gets delivered and the other gets queued with no notice to the user. I am sure that since we are doing whiz bang AJAX that we could tell the user the approximate wait time even after they are in the queue though. Cheers - L~R	[reply]
Re^2: How to emulate queue for CGI script? by Gangabass (Vicar) on Mar 21, 2011 at 16:33 UTC
Thank you for idea. Here is code i have now: Read more... (6 kB)	[reply] [d/l]