What if a timer does not run, if you set schedule through its runtime property?

Olivier Carneiro

Question

Cenario:
-A timer has no schedule assigned
-The «next run» of the timer is dynamically assigned at runtime, throught its schedule runtime property

In this cenario, the timer may stop waking up. How?
Supose you want the timer to run every 5 minutes. Each time the timer wakes up, you can assign its schedule, for example «Timers.MyTimer.Schedule» as «Substr( AddMinutes(CurrTime() , 5 ),11,5)».

But what if a SQL connection problem occurs (timeout, network problem, whatever) and the execution is aborted? The schedule will not be updated, causing that your timer will only start running from within 24hours. Why? Because the Schedule has a time value lower than the last run.

Let's instanciate:
-schedule has set to 13:00
-Timer waked up at 13:00:10
-The timer action assigned the timer schedule to 13:05, but a SQL problem occurred and the transaction was aborted, so the schedule wasn't set.

In this situation, the timer will only wake tomorrow at 13:00.

What is the solution?
The solution is to create a schedule that is a «time window» over the timer timeout. That is, for the above example the schedule shall be assigned with «13:05 13:10 13:15 13:20 13:25 13:30», assuming the default timer timeout of 20 minutes. This way, whether your timer fails or not, it will always wake up again.

Good work,
Olivier Carneiro

03 Mar 2006

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