RE: Java and CPU

["Larry Loen" <lwloen@xxxxxxxxxx>]

Kelly Cookson wrote:

>I'm still new at this, but my understanding is that
>optimization on the AS/400 involves translating
>bytecode files into *FILE objects that contain native
>machine instructions.

Pretty good for being new.  In the architecture of OS/400, we have a notion
of
persistent object.  Ordinary files exist as do data base files.  But, we
have many things
that are not really files (like programs).  On OS/400, you cannot read or
write
a program object under any language.  Moreover, because even "files" (IFS
files
in particular) are "objects" under OS/400, we can do things that regular
files
on other systems can't do.

So, the native machine instructions you mention are indeed attached to
the IFS files containing the .class or .jar information.  And, just as you
expected,
the original information is unaffected.

In fact, you can FTP any .jar or .class file that has an optimized program
attached to it, but it will come across "normally" without the added
machine
instructions at all.  There are also Java classes that can inspect .class
and
.jar files as well and these all run exactly as they do on any other
platform.

Finally, one should recall that while almost everyone does it, one does
not absolutely have to do this "covert attachment" of programs.

Also, in V4R5, one can force all classes to be JITed, which means that
one can do debugging without worrying about the effect of optimization,
because one can, in effect, shut it off for the debug run by instructing
the JVM to JIT everything for the current invocation of the Java command.
I don't have the exact command string memorized, but it should
come clear from the regular JDK documentation.

With only a bit of work and imagination, one should be able to do
most of one's debug on the client machine with an IDE; I do little
formal debug on the '400 myself and yet deploy to the '400 proper.

One key trick:  Encapsulate, with a simple object hierarchy, the
distinction between using the Toolbox driver and the Native driver.
This lets you use the toolbox for remote (PC and IDE access) of
the DB and the faster native access when you deploy for real.



Larry W. Loen  -   Senior Java and AS/400 Performance Analyst
                          Dept HP4, Rochester MN


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