RE: threading in rpg. was RPG and Web.. (was Using OO conceptsinRPG)

["Steve Richter" <srichter@xxxxxxxxxxxxx>]

-----Original Message-----
From: rpg400-l-bounces@xxxxxxxxxxxx
[mailto:rpg400-l-bounces@xxxxxxxxxxxx]On Behalf Of Hans Boldt
Sent: Wednesday, May 21, 2003 8:10 AM
To: rpg400-l@xxxxxxxxxxxx
Subject: Re: threading in rpg. was RPG and Web.. (was Using OO
conceptsinRPG)


Steve Richter wrote:
> As of V5R2, with IO direct into a data struct, procs dont have to use any
> global variables.  And if files are opened and accessed using some sort of
a
> handle, then file I/O could be thread safe.
>
> Interestingly, a lot of the changes that would make an rpg proc
threadsafe,
> like no global mapping of fields thru a data struct, file opens that are
> local to a proc and passed with a handle from proc to proc, would make the
> code more modular and less error prone.

Hans replied:
>Steve: I think you're still missing something here. If the only
>issue were user defined variables, there would be no problem with
>threading. At least there wouldn't be a problem for the compiler -
>all the synchronization issues would fall squarely on the back of
>the RPG programmer.

>No, the problem is with the compiler-generated
>internal data structures.

>Things like file control blocks and
>feedback areas,

If the programmer serializes file i/o, no problem?

>and also data structures involved with the RPG
>exception model.

and the compiler serializes exception handling.

But I guess there is also the matter of the program which created the 2nd
thread ending and its storage for io and exception handling being removed
from the stack.  while the 2nd thread is still running.  that would be
nasty.

This has me thinking about RPG ILE modules containing static variables
compared to C modules that dont have to have statics.  Does that mean that a
static (global) variable free module is quicker to startup and call into
than an RPG module?

>If you really think you have to do a threaded application, and you
>want part of it RPG, go right ahead. The way to do it now would be
>to write some of your code in C, which calls RPG procedures in
>modules compiled with THREAD(*SERIALIZE).

If I understand the limitation that Barbara described yesterday, when a proc
in a THREAD(*SERIALIZE) rpg module is called, the call will wait for any
other threads that are in any proc in that module to exit first.  If I have
that correct, that is a bit clunky and would actually degrade performance.

>If you can understand all
>the issues involved with threading, you can certainly handle a bit
>of C programming. ;-)

If a programmer can handle RPG they can handle any language!

-Steve