Need a server-side timer (independent of browser)

I'm putting together a website that will track user-defined events with time limits. Every user would be free to create events, and when the time limit expired, the server would need to take some action based on the outcome of the event. The specific component I'm struggling with is the time-keeping: think like eBay's auction clock -- it's set to expire at a certain time, clearly runs server-side, and takes some action when the time runs out. Searches for a "server side timer," unfortunately, just bring back results for a timer that gets the time from the server instead of the client. :(

The most obvious solution is to run a script on the server, some program that would watch all the clocks and take action when any of them expired. Tragically, I'll be using free web hosting, and sincerely doubt that I'll be able to find someone who'll let me run arbitrary stuff on their servers.

The solutions that I've looked into:

Major concept option 1: persuade each user's browser to run the necessary timers (trivial javascript), and when the timers expire, take necessary action. The problem with this approach is obvious: there could be hundreds, if not thousands, of simultaneous expiring timers (they'll tend to expire in clusters), and the worst case is that every possible user cou开发者_开发问答ld be viewing their timer expire. That's a server overload waiting to happen at the worst possible instant.

Major concept option 2: have one really trusted browser, say, a user logged in to the website as "cron" which could run all of the timers at once. The action would all happen in that browser's javascript, and would work great, as long as that browser never crashed, that machine never failed, and that internet connection never went down.

As you can see, I feel like I'm barking up the wrong forest on this problem. Some other ideas that have presented themselves:

I'm wide open for ideas -- I've started playing with concepts in JS and PHP, but I'm not tied to any language, particularly. The only constraint, really, is that I won't own the server that I'm running the site on, so I can't just run a neat little local process that does what I need it to do. :(

Any thoughts? Thanks in advance,

ASP.NET has multi-threading. You can have a static variable to collect the event data, and use a thread to do whatever needed when the time comes. After you can empty the static variable so it's ready for future use.

http://leedale.wordpress.com/2007/07/22/multithreading-with-aspnet-20/

You might want to take a look at the Quartz scheduler for Java which also has a .NET version. With a friendly open source license (Apache 2.0) this is probably a very good starting point.

If you can control cron jobs, which at least I could on HostPapa's shared hosting, you could run a php file every second which checks the timers and takes action based on them.

I would suggest AJAX anyway, what we did on a game server was emulation of "server connects to client" via AJAX request to server without any time-out (asynchronous connection). Basically you create one extra connection for each client that hangs on the server and waits for the server to take self-invoked action. After the action is done you start a new hanging connection immediately so you have one hanging all the time (so the server can talk to your client any time it wants). You can send javascript code from the server that will decide what will happen next. You can check clients to have these hanging connections on the server side to count as valid and of course run your timers on the server.