On Fri, 2009-01-16 at 13:46 -0600, Tim Nelson wrote:

Greetings list-

I'm on the hunt for a cron scheduler that supports definitions to the second. Obviously, every cron daemon supports minute/hour/etc but I have a special application that requires finer granularity.

I know I know... someone will say "The load will be horrendous on your system" or "Why don't you simply schedule your cron every minute and make up the higher precision in your application?". Unfortunately, this will not work. I really need a cron daemon that can schedule to the second.

All ideas/thoughts/suggestions/etc welcome. Thank you!

If the other suggestion doesn't meet your needs, consider the following.

Even a cron scheduler with 1 second resolution _may_ not give you what you need. This is because initializations may cause the application to start running too late. This possibility seems probable based on the need for 1 second resolution.

Of course, you could set the cron to kick off some average number of seconds earlier, but variability of system load, cache contents, disk I/O status, etc. could cause it to start sooner or later on any given invocation.

IMO, any application designed to need 1 second resolution (if that is the case here) should run as a daemon and handle the timing needs itself or accept signals (such as SIGUSR1 or whatever) from an external "supervisor" that tells the daemon "do it now". That way everything is already in memory (presuming swap is disallowed) and only system controlled resources, such as cache, buffers and disk I/O status could cause high variability. Those issues can be handled by ensuring load versus capacity is adequate during critical times. Of course, that might also then allow a cron-like dispatching process to be adequate for the task. It just depends on the host configuration for resources and load.

Tim Nelson

<snip sig stuff>

If this is for a process control application with tight timing constraints, I suggest a system dedicated to the task. Long ago and far away, I designed and implemented a custom hardware and software system to capture many items of data from a large number of textile looms. This was before such was available "off the shelf". It ran on a true UNIX system on 486DX/2 and 586 hardware. From that background I can strongly suggest dedicated hardware if your application is similar.

I'm on the hunt for a cron scheduler that supports definitions to the second. Obviously, every cron daemon supports minute/hour/etc but I have a special application that requires finer granularity.

I know I know... someone will say "The load will be horrendous on your system" or "Why don't you simply schedule your cron every minute and make up the higher precision in your application?". Unfortunately, this will not work. I really need a cron daemon that can schedule to the second.

Why wouldn't a wrapper script run at the minute and sleeping xx seconds before running the application work out?

JD