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Re: Confidence indicators for procedures.


From: Ben Pfaff
Subject: Re: Confidence indicators for procedures.
Date: Mon, 02 Jul 2007 08:24:07 -0700
User-agent: Gnus/5.11 (Gnus v5.11) Emacs/22.0.99 (gnu/linux)

John Darrington <address@hidden> writes:

> Executing procedures involving very large data sets obviously takes a
> finite time.  If people are going to have confidence in the GUI, they
> need to have some sort of indication that the procedure is running,
> and an idea of how far it is away from completion.

It is going to be pretty easy to produce an indication that a
procedure is running, I think.  

> It is possible to add some sort of callback in procedure.c and/or
> casreader-*.c ?  (There are a number of while loops --- I'm not sure
> which will need attention)  

It depends on what you want to measure.  If you want to measure
how much of the active file has been read, then you could put a
callback at the beginning of proc_casereader_read, outside the
loop.  Then you'll get a call every time a case is read from the
active file.  (If the procedure makes multiple passes you'll only
get a call the first time a given case is read.)

How far a procedure is from completion is more difficult, of
course, because there's no way to tell how much processing is
going to happen, how many passes the procedure will make, etc.

> The trick is, not to allow the confidence indicators themselves
> to significantly increase execution time.  So instead of
> reporting at each iteration, it would be best to report at
> pre-determined intervals of real time.

One possibility:

signal(SIGALRM, sigalrm_handler);
setitimer(ITIMER_REAL, ...);

sigalrm_handler()
{
   alarm_triggered = 1;
}

In the callback:
   if (alarm_triggered) {
     alarm_triggered = 0;
     ...update indicator...
   }

There's a race between test and reset in the callback but we
really don't care in this case.
-- 
"The sound of peacocks being shredded can't possibly be
 any worse than the sound of peacocks not being shredded."
Tanuki the Raccoon-dog in the Monastery




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