how to create php scheduled process?

Question

Hi,

I was asked to create an web apps that will send updates to user for certain time.

for example

1. user1 asking for updates every 5 minutes from June - August 2009
2. user2 asking for updates every 10 minutes for today only
3. user3 asking for updates every 1 day from june - august 2009

I have no idea how to automatic the background process ... should I add to cron ? can cron works on windows server (apache on windows) ?

Answer 1

windows doesn't use cron, but I think it does have some sort of scheduling. The answer, in general, is yes, cron jobs are the way to run those in the background.

Answer 2

Define updates.

Do you mean an updated page? (I guess not, since you could simply refresh the page when the time was up, using Meta Refresh or Javascript...)

Do you mean e-mails?

Answer 3

On a Windows Server you can write scheduled tasks. In a scheduled task you can set it to run the update to the frequency you want.

From the Microsoft Knowledge Base:

With Scheduled Tasks, you can schedule any script, program, or document to run at a time that is most convenient for you.

A more programmatic approach would be to save the settings from your users and the last update time. Then you can have a script that checks that and runs the update as required.

You can have a scheduled task to run that script every minute or so which will do the updates based on your users' settings.

Answer 4

If you are on a dedicated server, you can use the System Tools > Scheduled Tasks on windows server. If you really can't change anything on the server, you can try to run cron on an Linux server, sending a request to your windows server... hehe

Answer 5

I have just written a project that uses Apache, PHP and scheduled tasks under Windows XP and 2003. It's pretty easy, and works similar to cron.

One thing to note - the GUI controls for scheduled tasks are not as granular as the command line. I wasn't able to schedule any more frequently than once a day. Fortunately, you can use the command line to do this.

schtasks /create /sc minute /mo 10 /st 00:00:00 /tn "Task Name Here" /ru "System" /tr "C:\wamp\bin\php\php5.3.0\php.exe \"C:\Program Files\script.php\""

This creates a scheduled tasks that runs every 10 minutes (starting at midnight), called 'Task Name Here', under the 'System' userid. Do you see the escaped quotes around the path? You will need to put escaped quotes around paths that have spaces in them.

Answer 6

As suggested by Marcel, I'd create a single cron job (*nix) / scheduled task (Windows), and have it run once a minute or so.

This job would then look through all the users' update subscriptions, determine which require a new update to be sent, and send them. Obviously, you'll want this job to complete in less than a minute (if the job runs every minute), which may be a problem if you try to process many users in one go.

I would not recommend trying to create and manage cron jobs / scheduled tasks from within PHP. It's much easier to set a single job up once, then handle the rest in PHP code.

If cron jobs / scheduled tasks don't work out for you, you can also consider piggy-backing on ordinary requests to your website. This is e.g. how Wikipedia's MediaWiki software handles background tasks – they're pulled off a job queue and processed as part of unrelated page requests.

Answer 7

Add a Cron or Scheduled task that executes at your lowest common interval (5 minutes? 1 minute?).

The scheduled task should query a database table that holds info on the frequency of the user's task. I would express frequency in seconds, then use a UNIX timestamp to determine eligibility for execution. The computation is then somewhat easy:

• Find the current time, rounded down to nearest common interval (assuming a 60-second interval): NOW = TIMESTAMP - (TIMESTAMP % 60)
• Find users whose interval is an even divisor of the current time period

The table could look like this:

CREATE TABLE `scheduled_tasks` (
  `id` int(7) unsigned NOT NULL auto_increment,
  `user_id` int(7) unsigned NOT NULL,
  `task` varchar(32) NOT NULL,
  `interval` int(10) NOT NULL,
  `date_start` date NOT NULL default '0000-00-00',
  `date_end` date NOT NULL default '2030-12-31', -- Hopefully you won't be still maintaining this app 
  PRIMARY KEY  (`id`)
) ;
INSERT INTO `scheduled_tasks` (user_id, task, interval, date_start, date_end )
VALUES
  (1, 'standard_job', 5*60,  '2009-06-01', '2009-08-01'),
  (2, 'standard_job', 10*60, CURDATE(),  CURDATE() ),
  (3, 'standard_job', 24*60*60, '2009-06-01', '2009-08-01')

To find jobs to run, this query could work:

SELECT `user_id`, `task`
FROM `scheduled_tasks` 
WHERE (UNIX_TIMESTAMP() - (UNIX_TIMESTAMP() % 60 ) ) % `interval` = 0
  AND CURDATE() BETWEEN `date_start` AND `date_end`

That comes back with a list of users/tasks to run. You can add multiple entries per user if necessary.