[SS] 16Dec2004:

A Tcl user had a problem in the Tclers chat with timers and syncronization.
The problem is to execute some code every 30 minutes, but syncronized with
the real clock of the comuter. So at 01:00, 01:30, 02:00, and so on.


The following procedure should do just it, but it's possible to change the
timer period modifing the 'every' variable that's hardcoded to 1800
in this example.


I didn't tested the code a lot... so if you need to use it in a critical application
please do some test. 

 proc cron {{opt {}}} {
     set every 1800
     if {$opt eq {}} {
        # Do the work you need every $every seconds
        puts [clock format [clock seconds]]
     }
     after [expr {($every-([clock seconds] % $every))*1000}] cron
 }

 cron -init
 vwait forever