Re: how to let my program sleep a while

[booth@xxxxxxxxxxxx]

How could such a simple procedure teach me so much?  Well it is.  Thank 
you folks. 

Next question: Simon and others have spoken of passing in the SleepFor 
value as a 5 digit value.  Why isn't it passed as *HMS?  the procedure 
itself can add the *HMS to the current time, or whatever.  The added 
benefit is that then there is no issues as to how many seconds in 42 
minutes.
 
_______________________
Booth Martin
Booth@MartinVT.com
http://www.MartinVT.com
_______________________




"Simon Coulter" <shc@flybynight.com.au>
Sent by: owner-rpg400-l@midrange.com
09/20/2000 12:40 AM
Please respond to RPG400-L

 
        To:     RPG400-L@midrange.com
        cc: 
        Subject:        Re: how to let my program sleep a while

?
Hello Booth,

You wrote:
>As usual your suggestion is best.  Much better.  Two procedures it shall 
>be.  Now, (every body skips over the easy stuff!) why do I want to use 

>"CallP   Sleepfor('00:30:00')" 

>instead of 

>"Call   'SleepFor'"
>"Parm   '00:30:00'    Parm8       8"

Because CALLP requires a prototype which the compiler uses to verify that 
the data type 
specified on the prototype is compatible with the the type of data 
actually used on the 
call.

With CALLB (and indeed with CALL) the invoker can pass any old crap to the 
procedure. 
Prototypes help make robust software by catching stupid programmer 
errors** during 
compilation rather than run-time.  It's not perfect but it a bloody sight 
better than 
the alternative.

Barbara's comment on the choice of names is correct (and in fact the 
choice of name is 
the single most important aspect of a procedure).  In this case you have 
two similar but 
different procedures.  They need different data types.  sleepFor() needs a 
duration but 
sleepUntil() needs an absolute time.  You should define the prototypes 
accordingly e.g.,

D sleepUntil             PR
D  time                                                           T  VALUE 
TIMFMT(*HMS)

such a prototype will stop the caller from passing character or numeric 
data unless it 
can be converted by the compiler into the correct type.  Since RPG doesn't 
have a 
duration data type we need to content ourselves with a numeric value of 
some sort e.g.,

D sleepFor               PR
D   duration                                             5I 0 VALUE

but at least that limits the possible sources of crap data.  The onus is 
still on the 
programmer to pass the correct stuff but with prototypes you can restrict 
the truly 
creative.  (You may decide to design sleepFor() to accept a time data type 
and then 
convert it to a duration -- you might choose to interpret the time as an 
offset from 
midnight and the procedure will sleep for that many hours, minutes, and 
seconds.)  In my 
example from a few days ago I defined the parameter as a 6,0 packed field 
because the 
range of allowable values on DLYJOB is 1 to 999999.

Now see if you agree that the two procedures described above are better 
than one like 
the following:

D sleep                          PR
D   delay                                                5I 0  CONST 
OPTIONS(*OMIT)
D   resumeTime                                            T    CONST 
OPTIONS(*OMIT:*NOPASS)

I know a lot of this appears to be simply style but think about it for a 
bit -- and read 
some stuff on Object Oriented (not Orientated!!) Design.  Two good books 
on the subject 
are:
                 Designing Object Oriented Software by Rebecca Wirfs-Brock
                 Design Patterns by Erich Gamma et al.

These books should be on all programmer's bookshelves alongside the 
well-thumbed 
3-volume (unfinished) set by Donald Knuth.

Note that you may choose to create just such a sleep() procedure to do the 
real work and 
then wrap it in a facade using the first two prototypes.  It depends on 
how important 
abstraction and encapsulation is to you.  In this case sleep() would be 
private while 
sleepFor() and sleepUntil() would be part of the public interface.

>I understand that for most of you this is pretty basic, but hey, I just 
>don't know the answer.

And now you do :)

** (i.e., those errors that are human mistakes rather than errors made by 
stupid 
programmers -- nothing shields you from those)

Regards,
Simon Coulter.

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