Re: FW: java to RPG problem

["Blair Wyman" <blairw@xxxxxxxxxx>]

> The question is: how can the [RPG] program know which is the correct JVM
to
> attach
> to? For example, there may be a requirement always to attach to a given
WAS
> JVM instance. I suppose an alternative would be to customize the WAS
> instance, on start up, to call out to RPG in order to insure that the WAS
> instance is known to RPG.

Alexei is right.  You can only "attach" your thread of execution to a JVM
that is in the same process (i.e. *JOB) with you.

IIRC, the RPG->Java runtime creates the JVM only if it needs to, and will
use an existing JVM if one is found.  (That's what the
JNI_GetCreatedJavaVMs stuff is doing).

So, yup, you could call an RPG native method in a class running in WAS, and
theoretically that RPG native method can use the nifty RPG->Java codings to
get back into Java.  BUT, it becomes YOUR responsibility to understand the
*extra* synchronization required by RPG in this context.

Java is inherently threaded, often very widely in a webserver, so the
*MODULE-level mutual exclusion in RPG could definitely "surprise" your
webserver if it presumed a certain inter-task "independence" at runtime.
(I'm not saying it does...  Just speculating.)

I mean, suppose a webserver decided that some "request handling" task was
sufficiently isolated that it could "hand out" the task to many parallel
threads.  The webserver would expect a nearly linear speedup, up to and
depending on the number of physical processors on the machine, but could be
stymied if there was a "thread join" going on "under the covers."

And, as has already been noted, leaving out the H THREAD(*SERIALIZE) is
perilous behavior, indeed.

HTH.

-blair

Blair Wyman -- iSeries JVM -- (507) 253-2891
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
"It is a sobering thought that when Mozart was my age,
he had been dead for two years." -- Tom Lehrer