🚀 go-pugleaf

[Offering to the great line eating god - may it serve you well...]

"I am looking for a way to cause my program to take an exception so that
  it can write out the intermediate results of a long calculation..."

Thanks to everyone who mailed/posted answers to my inquiry about checkpointing
a processing task.  The current scorecard reads as follows:

    1) I can poll for some external signal (CheckAbort() seemes to be best)
        and write out results when the signal arrives. Generate the signal
        with another CLI spawned task.

        [I knew this. This method is not what I want to do, since my "loop"
           executes a quingigillion* times for each problem.]

    2) Determine algorithmically (as in "count the number of iterations") 
        the appropriate time in the loop to put checkpoint code.

        [Again, unsuitable unless absolutely necessary. See answer to #1.]

    3) I cannot use software or hardware interrupts, since I won't be able
        to do anything useful during an interrupt.

        [I agree - whoever wrote this section of the OS must have failed
            or forgotten their intro to OS course.]

    4) I can use an external process to checkpoint the calculation process
        by having the calculation process send the checkpoint process the
        address of the calculation data. Generating an external process,
        however, is cumbersome.

        [A tolerable solution, but messy! Having shared data is very poor
            style, and leads to bugs. May be necessary in this case, though.]

        [This particular problem does not need synchronization between the
            two tasks. In the general case, semaphores (or something) would
            be needed, and solution #1 would probably be faster.]

        [Actually, I would have generated the checkpoint process from the
            CLI and have the two processes communicate via a public message
            port. This seems a lot cleaner than trying to generate one
            process from within another. Or am I missing something?]

    5) I can setup an exception handler for the timer message: when the
        message is delivered, my process will be interrupted and forced
        to call the specofied routine.

        [Just what I was looking for (my thanks go to Bill Kinnersly!).
            Howcome this isn't mentioned in the documentation?]

*Quingigillion: The number of miles from the electric monk to Salt
                   Lake City, Utah.

-- 

Joel Jennings   | Wampeters, foma, and granfaloons.
                |