PHP在动态时运行脚本？ 为cron工作还是不工作？

Question

I need to run scripts at dynamic times (coinciding with a datetime in a database). Any ideas how to accomplish this?

Example:

Database says tomorrow at noon in 1 in a datetime field, then i want to run the script tomorrow at noon.

Answer 1

A very simple approach is to have a cron-job call a PHP script every 1 minute, and have it check the database for things that need done. If something needs done NOW(), then do it and remove from database.

You need to consider things like locking, process stacking, multiple processes, etc... to make this robust. But if your need is simple, this is a simple way to make it work.

Add this to crontab:

* * * * *   /usr/bin/php /path/to/my/script.php

And in /path/to/my/script.php

<?php
$ts = time();

// Run for up to 50 seconds
while($ts + 50 > time())
{
   ... SELECT id, job_stuff FROM JobTable WHERE JobDate <= NOW() ...

   process job

   ... DELETE job_stuff FROM JobTable WHERE id = ...

   sleep(5);       
} 

Note, this is not robust. A robust script would grab a record while locked, update it to a "processing" status, process it, and update it to a "complete" status. This means that multiple processes could work at this same time (even if accidental) and not duplicate jobs. Also, this means that a single failure would not stop the train.