Just in case you didn't know: Did you have a look at the Quartz Scheduler? http://www.part.net/quartz.html http://www.part.net/quartz_features.html Perhaps it already does what you need. It's licensed under a BSD and Apache-Style license.
Here's another one: http://jcrontab.sourceforge.net/
I found the links on this page: http://wiki.cocoondev.org/Wiki.jsp?page=WyonaScheduler
Bye,
AndreasGiacomo Pati wrote:
On Sun, 31 Aug 2003, Bruno Dumon wrote:
On Sun, 2003-08-31 at 20:38, Giacomo Pati wrote:
First, if you look at the Cornerstone Scheduler you'll see that the ability to define repeated tasks are somehow limited. Business apps can easily request administration tasks to be run twice a day on work days. To define this with the Cornerstone Scheduler you'll need to add 10 'cron' entries to it. This is why I'd like to extend it using the unix cron direction to define ranges and list of timing aspects. But then you're faced with the problem of defining sleep time for efficient use (which you need to be able to cooperate in the Cornerstone Scheduler machinery).
The unix cron daemon runs every minute to check if there are any jobs to run. It checks initially creating bitsets for the minute, hour, day, month, and weekday definition for each task. This makes it easy to check whether a task has to be launched. I still haven't found an algorithm (and I think there isn't an easy one available) to determine the sleep time until the next task is due.
Ah, didn't think that far.
Thus, a check every minute isn't much but still 1440 times a day.
But a lot less then the 864000 times a day in case of a check every 100 ms :-)
Sure.
The other thing to respect if you'd like to go as efficent as possible is the determination of Threads you'll need to run each cron task at the time specified. But this needs knowledge about how much elapsed time a task need to run to decide if you need one or two thread to complete to task defined neat in time to each other. If you have an algorithm for this you'll be able to define the maximum numbers of Thread you'll need. Otherwise you allocate a separate Thread per defined task.
The consequences are that probably the easiest solution to a (more or less) complete Cron like Scheduler is an own heart beat of one minute to check for task to launch and a pool of Threads as big as you have task to process. As it seems Doug Leas concurrency tools could be configured to be as resource sparing as possible (have a look at http://gee.cs.oswego.edu/dl/classes/EDU/oswego/cs/dl/util/concurrent/PooledExecutor.html)
Yep, I think that will be fine too.
Ok, so I'll gona build up a Scheduler based on its own heart beat (own Thread) with Crond expressions for timing specifications that uses a PooledExecutor for the Triggers in the size of the numbers of Task defined in the configuration but with lazy construction of Thread objects. This will not need any additional jars and the ones introduced by the Cornerstone Sccheduler can be eliminated again. Is everybody happy with that?
-- Giacomo Pati Otego AG, Switzerland - http://www.otego.com Orixo, the XML business alliance - http://www.orixo.com
