Re: Bug Found causing slowdown and errors... And a question onscope ofobjects

["David Morris" <David.Morris@xxxxxxxxxxxxx>]

Brad,

In addition to the JVM, there a boundary (a lot like an activation
group)
may be set by using a different class loader.  You can see objects
created by class loaders higher up the tree from a class, but you
cannot see objects on different branches.

Here is a reference that explains this a lot better than I can:

http://jakarta.apache.org/tomcat/tomcat-4.0-doc/class-loader-howto.html

David Morris

>>> lwloen@us.ibm.com 01/10/02 04:57PM >>>

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