RunScheduledTask didn't execute itself the first time, why?

Question

I have a problem with RunScheduledTask (new in Mathematica 8).

A task that I usually need to do is to set a cron to start at a specific time and repeat itself at the same time every day (or the same minute every hour, and so on...)!

Let's make an example: suppose I have to run Pippo[] at 5:00 AM every day starting from tomorrow. These are the "logic" steps in my mind to do so:

• calculate the absolute time of tomorrow at 5:00 and save it to ABSTIME
• execute RunScheduledTask[Pippo[], 60*60*24, ABSTIME]

Unfortunately I have discovered that if I make it this way IT WON'T EXECUTE tomorrow at 5:00, but it will start the day after. I tried to set as ABSTIME the absolute time of today at 5:00 but it doesn't work either ('cause the ABSTIME is in the past). The only work-around I found is:

• calculate the absolute time of tomorrow at 5:00 and save it to ABSTIME
• calculate amount of seconds from now to tomorrow at 5:00 and save it as SECSREMAINING
• execute RunScheduledTask[Pippo[], {SECSREMAINING}] for the execution of tomorrow
• execute RunScheduledTask[Pippo[], 60*60*24, ABSTIME] for all other executions

I think this a very "an-elegant" way, do you have any other solution? Or should we mass-warn Wolfram about this and make it change? ;)

Answer 1

Can't you do something like

RunScheduledTask[Pippo[]; RunScheduledTask[Pippo[], 60*60*24], {0}, ABSTIME]

Answer 2

I have tried this on both a mac and a pc using MMa 8.0.4 and it works as advertised. If the time is in the past the task will execute instantly. I have tried the following and got the expected result:

RunScheduledTask[MessageDialog["text"], {1}, AbsoluteTime[] + 5]
RunScheduledTask[MessageDialog["text"], 5, AbsoluteTime[] + 5]

If I execute the code below with a time in the past I get the dialog straight away.

RunScheduledTask[MessageDialog["text"], {1}, AbsoluteTime[] - 5]

Are you running 8.0.1 or 8.0.4?

Edit

I think I do understand now what you are after and have the following code snippet

repetitionTime = 10;
scheduledStartTime = 5;

printMessage[] := Print["Task executes. Time: ", DateString[]]

RunScheduledTask[
 Block[{}, ResetScheduledTask[$ScheduledTask, {repetitionTime}]; 
  printMessage[]; 
  StartScheduledTask[$ScheduledTask]], {scheduledStartTime}]; \
Print["Start time: ", DateString[]]

This task will start after scheduledStartTime seconds and will execute every repetitionTime seconds. It is not adding the repetition time to the start time. In this case the first printMessage is executed after 5 seconds and is then repeated every 10 seconds.

Hope this helps.