Re[2]: RPG on other platforms...

[Buck Calabro <mcalabro@xxxxxxxxxxxx>]

>Jim Welsh wrote:
>
> I've been asked by my employer to do some research on the effects of
> running an RPG III
> program on platforms other than the AS400.
>
>As far as your information on reentrant goes: All programs on the AS/400 are
>reentrant by nature.  There is no special coding required.  The compiler 
>creates
>an object which contains the instruction set and base memory offset to the 
>data.
>Each user upon calling the program will be assigned a base memory address for
>their data and control information to track the current instruction being
>executed.  So A + B = C turns into OffsetForA + OffsetForB = OffsetForC and is
>executed as (UserBaseAddress+OffsetForA) + (UserBaseAddress+OffsetForB) =
>(UserBaseAddress+OffsetForC).

Kind of an interesting way to look at the PAG, but it gets the idea across!

>Special coding was required for the S/36 MRT programs which were a crude 
>attempt
>at reentrant concept: one copy of instructions, many copies of data.

All too true!  
But is Jim asking about re-entrancy or recursiveness?

Re-entry means that no matter how many people are using a program,
only one copy is active in memory at once.  Recursiveness means that
RPG program A can call RPG program B who can call RPG program A
again.  That's not allowed in OPM RPG (sadly, I haven't checked for
ILE.)

Once Program A is in the job's call stack, it can't be CALLed again
or you'll get:
Message ID . . . . . . :   RPG8888       Severity . . . . . . . :   99        
Message type . . . . . :   Inquiry                                            
Date sent  . . . . . . :   02/24/98      Time sent  . . . . . . :   15:36:19  
                                                                              
Message . . . . :   CMD called itself recursively (C S).                      
Cause . . . . . :   The RPG program CMD called itself or another program which
  then called program CMD.                                                    
Recovery  . . . :   Enter C to cancel, or S to obtain a system dump.          
Possible choices for replying to message . . . . . . . . . . . . . . . :      
  C -- Cancel                                                                 
  S -- Obtain system dump                                                     

Buck Calabro
Commsoft, Albany, NY

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