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On Mon, 16 Jan 2006, Scott Klement wrote:
Somewhere in the guts of the operating system (or maybe this part is in hardware, not sure) there's a big loop that loops through all of the active jobs. As each job comes up in the loop, it gives that job a certain amount of time to execute code (a "timeslice") before moving on to the next job.
In the linux world this loop is called the scheduler. There is quite a bit of interesting reading regarding different ways of implementing the scheduler. lwn.net is a good source for reading up on it. Obviously the linux scheduler and the iSeries equivalent won't be the same, but for the curious it is quite interesting.
There's one option that I haven't seen discussed... setitimer(). You could use that with a signal handler to have a subprocedure that's run at a given interval. This might be an interesting option if you need to run things on a given interval, such as 2 minutes. Using sleep() won't do that. If you sleep for 120 seconds, then run a porgram, then sleep for 120 seconds, does the program run every 2 minutes? No, because the program takes time to execute. For example, if the program takes 30 seconds to run, then it's being run every 2:30. Two minutes for the sleep, and 30 seconds for the program itself to run. If you used setitimer() it would actually run every 2 minutes instead of 2:30 because the signal handler gets called every 2 minutes without regard to what it does in between. (Unless, of course, it's runtime actually exceeds the interval time... for example, if you called a program that took longer than 2 minutes...)
Actually I coded up an example that uses setitimer() and also avoids the problem discussed in the paragraph above. My example also uses signals to terminate the program gracefully. My example is in C but you could call RPG subprocedures from the C code to do what you want. My example is here:
http://archive.midrange.com/c400-l/200511/msg00007.html James Rich It's not the software that's free; it's you. - billyskank on Groklaw
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