RE: Bug Found causing slowdown and errors... And a question on scope of objects

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Apologies if I'm barking up the wrong tree again Brad,

>From your earlier comments, I assume you are running on a PC accessing a
local Access DB. So I guess you are doing something like:

* Open a dos window, and run the endless loop program by running the "java"
command. This runs forever, so never returns to the command line.
* Open a second dos window, and run the second program, again by invoking
the "java" command.
Correct so far?

If so then your test doesn't seem to work because each time you run the java
command you are invoking a new JVM, with it own set of static variables. For
get the kind of response I think your looking for, both "programs" would
need to be invoked from within the same JVM, perhaps as separate threads.

Chris.

 -----Original Message-----
From:   Brad Stone [mailto:brad@bvstools.com]
Sent:   11 January 2002 04:02
To:     java400-l@midrange.com
Subject:        Re: Bug Found causing slowdown and errors... And a question
on scope of objects

Thanks Larry, makes sense.

But (or course...) I've been doing some tesing on my
Database Connection Manager.

I run a program that creates three connections.  I use
methods to return the number of connections, free
connetions, and clients in use by the DBCM.  If I use this
during the running of the program, things work great and the
data returned is correct (ie it tells me I have 3
connections in use, and 0 in use after I reclaim those 3
connections).

Now, I put an endless loop in this application before the
three connections are reclaimed.  Just so that the three
connections will stay there.

Now I run another application to see if I can get the
instance data from the class created by the currently
running application.  It ends up creating another instance
of the Database Connection Manager instead of using the
already existing one.

Am I missing something here?  This DB Con Mgr class is set
up as a Singleton class, meaning that (I thought) if a
instance already existed, a new one was not created, and the
current existing instance was returned to the application.
So this 2nd application should return that I have 3
connections in use, or so I thought.

This doesn't seem to be the case in this scenario.  But it
is what I expected since both applications are running in
the same JVM.

Sorry if this is off topic or doesn't make sense.  I seem to
have my Java learning spurts from time to time.  Just let me
know (Joe) if this should be moved to Java101.

Brad

On Thu, 10 Jan 2002 17:57:07 -0600
 "Larry Loen" <lwloen@us.ibm.com> wrote:
>
> Forget activiation groups and such.  Java is platform
> independent, so it
> doesn't use such things.
>
> If Joe invokes a JVM, his static variable will be
> different from the JVM
> that Mary invokes separately.
>
> If, on the other hand, Joe and Mary both interact with an
> application
> (perhaps, via the web) that ends up being performed in
> different threads in
> the same JVM, then they will share the static variables
> of each class.
>
> The key is that it is the JVM that is the main boundary.
> Each new JVM is a
> bunch of new static variables.
>
> The benefit from connection pooling is, at minimum, reuse
> of the expense of
> creating the connection even for a JVM that consists
> entirely of one Java
> application and thread.  It can be more savings, though.
> If you want two
> "jobs" to share the costs and benefits, structure your
> application so that
> they end up as Java threads in the same JVM.
>
> Just remember that they aren't jobs in that case, but
> true threads with all
> the potential sharing that implies.
>
>
> Larry W. Loen  -   Senior Linux, Java, and iSeries
> Performance Analyst
>                           Dept HP4, Rochester MN
>
>
> _______________________________________________
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Bradley V. Stone
BVS.Tools
www.bvstools.com
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