How to take an action after certain time (different from user to user)?

Question

I'm developing a web game (js php mysql) in which one clicks a button to start an action that takes time to complete (let's say 10 hours) and when it finishes some points are added to that player's total.. The problem is that I need those points to be added even if the player is not online at the time the action finishes.. for example I need to have the rankings updated, or an email sent to the player..

I thought about a cron job checking constantly for ending actions, but I think that would kill the resources (contantly checking against actions of thousands of players..).

Is there a better solution to this problem?

Thanks for your attention!!

Answer 1

You can just write into your database when it's finished and when the user logs in you add the earned points to his account. You can also check with a cronjob. Even if you have millions of user this will not kill your server.

Answer 2

Cron is perfect for this. You could write your tasks in stored procedures, then have cron run an SQL script to call the stored procedure that would update the records of your players.

Databases are designed to work with thousands and millions of pieces of information efficiently, so I don't think the idea that it will kill system resources is a valid one unless you hosting system is really constrained already.

Answer 3

If you want to be safe against cheating you need to do the checking on the server anyway. If the "waiting" will happen within a Javascript on the client, one could easily decrease the remaing time.

So you need to send the job to the server (which is assumed to be safe against clock modifications) and the server will determine the end timestamp. You could store your jobs in a queue.

If you only need this information for the user himself you can just look at the queue when the user logs in. Otherwise run a cron job every minute (or so). This job will mark all jobs finished when their timestamp is in the past (and remove them from the database).

If you need more precise checking you will need to come up with an alternative server side solution that is doing this more often (eg a simple program polling the database every few seconds).