[wp-hackers] WP cron and "multi-threading"

[Owen Winkler]

I've used wp_schedule_event() to register a cron event during the 
activation of my plugin, and I have a couple of issues.

#1: The cron event seems to leave remnants of non-existent args in the 
serialized options array.  Every time it runs it adds an array wrapper 
to the existing zero-length array of arguments.  I don't know if this 
patch (http://trac.wordpress.org/ticket/3169) will fix it.  I'm not sure 
if it's causing any issues with the plugin itself since I'm not using 
the parameters, but I don't think it will be a problem, at least until 
the size of the data exceeds the field length.

#2: I need the cron to run *exactly once* at each interval.  Assuming 
that traffic on the site is buzzing along, the current cron 
implementation could allow events to be processed more than once, 
depending on how long it takes for the hooked function to run.  In my 
case, the computation in the cron hook usually takes 2 seconds or more, 
leaving plenty of room for another incoming hit to trigger the same event.

I've implemented a flock() check in my own code, something I'd rather 
not do.  It might be beneficial to rearrange the cron code so that it 
unschedules the event before it executes it.

Any other clever suggestions as to how to keep the cron from executing 
more than once on a single registered instance would be helpful.

Is anybody else using this functionality in their plugins?

Owen