RE: Is RPG 'DEAD"

And to even drive in the point even further, a quote from
http://java.sun.com/j2se/1.5.0/docs/api/java/lang/System.html#gc():

"Calling the gc method suggests that the Java Virtual Machine expend
effort toward recycling unused objects in order to make the memory they
currently occupy available for quick reuse. When control returns from
the method call, the Java Virtual Machine has made a best effort to
reclaim space from all discarded objects."

Note that calling the gc method only suggests that the JVM cleans up,
there is never ever any guarantee. I have read that the JVM is doing a
'best effort', but could not find any hard evidenced for that. It all
boils down to "don't ever think gc has cleaned up after you activated
it", as you have found out the hard way. The gc will receive your
suggestion but it will only do anything if it sees fit. It may defer
your suggestion to a later point because other high priority things need
to be done first or it was planning to do it at a later point, but it
may even completely ignore your request and only perform cleanups
whenever it sees fit (or even do nothing at all).

Cor

-----Original Message-----
From: rpg400-l-bounces@xxxxxxxxxxxx [mailto:rpg400-l-
bounces@xxxxxxxxxxxx] On Behalf Of Aaron Bartell
Sent: donderdag 19 juni 2008 14:13
To: RPG programming on the AS400 / iSeries
Subject: Re: Is RPG 'DEAD"

Just wanted to provide some input on the garbage collection and
OutOfMemoryError stuff you brought up Corr.

I wrote an entire Java application that ran on a Canon
copier/scanner/fax
machine (one of those with the big LCD touch screens) and it most
definitely
had the potential to run out of memory (to the point where I could

make

it
happen almost at will). Here is a section of code for how I trapped
memory
errors and *attempted* to free garbage. You should note that reading
Suns
garbage collection documentation is required to really understand what
is
going on. For example, the below System.gc() didn't always free up as
much
memory as I expected it to based on the document images I was
processing.
Anyways, take it for what it's worth...

try {
if (garbageCollect)
System.gc();
garbageCollect = !garbageCollect;

byte[] newCopy = new byte[oar.data.length];
System.arraycopy(oar.data, 0, newCopy, 0,
oar.data.length);
outStream.write(newCopy);
outStream.flush();

} catch (IOException e) {
Log.out(Log.getStackTrace(e));
} catch (OutOfMemoryError e) {
Log.out("!!!!!!!!!!!!!!!!!!Out Of MEMORY
ERROR!!!!!!!!!!!!!!!!");
Log.out(Log.getStackTrace(e));

ignoreRemainingImages = true;
if (currentJobId > 0)
Device.cancelJob(currentJobId);
readEnd();
UICommand.imageTransferError("ERR002", "Page " +
currentPage
+ " exceeded maximum image size.");

return false;
}

BTW, programming for hardware is pretty fun, but WAY different than
what I
am normally used to, but still quite fun once you figure out the

"flow"

of
setting up and tearing down communications.

Aaron Bartell
http://mowyourlawn.com

On Thu, Jun 19, 2008 at 1:23 AM, Takken, Cor <cor.takken@xxxxxxxxxx>
wrote:

It has been some time since I ever read such an entertaining (and

long)

thread. I will react only once and then lean back again and enjoy

this

thread.

First of all, I agree with all of you who have suggested that this
'consultant' should be asked to either name the IBM-guys and come up
with documents supporting this bold statement or resign his job (and
then climb some high mountains just to repent). RPG is not dead (or
alternatively: as dead as COBOL), and neither is Java or C#. All
languages have their purpose and right application, RPG is not for
high-end graphical applications and Java or C# have their strengths

in

other fields.

Now for some other things:

Java is better because it prevents memory-leaks (or words to that
extent).
Java as a language is not better. The language Java has no thing as

a

garbage collector, and it does not prevent memory-leaks. The virtual
machine which processes the Java code (or the intermediate compiled
bytecode) needs to implements a few interfaces. Implementing

interfaces

means that you need to accept calls to certain functions with

certain

parameters, however nowhere in the documentation of Sun does it say

HOW

you need to implement these calls. I would even put it a bit

stronger:

the Java documentation explicitly states that there is absolutely no
guarantee that calls to the garbage collection will guarantee

anything

to be cleaned up. Cleaning up after badly written programs is the
responsibility of the JVM, but if the JVM decides never to clean

up...

well then nothing is cleaned up, and at some point even the JVM will

run

out of memory and there is no try catch finally in the world that

will

catch this because no program will run. Is java then better? I would
argue that it is not (but I will stand corrected) since there is no

code

that will allow me to explicitly remove objects (it allows me to use
"new " to create objects, but is there a "old" or "cleanup" function

to

kill created objects?).

Classes are comparable to modules or service programs
RPG IV is not an object oriented language, Java is. Classes

represent

runnable code which can only be used once instantiated as an object
(barred static methods), modules and service programs can be

compared

to

static (so class-level) methods. Classes are abstract descriptions

of

objects, objects are instantiations of classes and represent a class

in

a certain state which can behave in a predescribed way (the code in

the

class) as is fit for that state. A module is not a class, a module

is

a

stream of code which can be called from the outside to perform some
functionality and that is it. A module is always a single thing,

there

is no way for an application to instantiate the same module in more

than

one instantiation and use them next to each other or simultaneously.

The

whole concept of RPG does not even allow this and while I appreciate
that there are ways to simulate such behaviour (e.g. copy the same
module to different locations or by renaming the compiled object)

that

would still be a simulation and not have the same flexibility as

object

instantiation. The whole programming concept of RPG is different

from

Object Oriented (or close to Object Oriented) languages as Java,

C++,

C#, etc. You can't compare the two except on the bare line to line

code

basis (comparing if-statements etc.).

And again: this consultant should either produce the hard evidence

of

the demise of RPG or forever hold his peace.

Kind regards,

Cor

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