Search This Blog

Thursday, December 24, 2009

Can I mix Terracotta with custom classloaders?

Today's challenge is going to be an interesting one.  As I often do, I'm attempting to mix a couple ideas together to see if something really interesting comes out.  Here's the context: I'm looking at Terracotta Distributed Shared Object technology for a project I'm working on.  It is a really slick way for distributing objects between JVMs without having to implement any custom infrastructure classes -- POJOs all the way, baby.  The application will be using Spring to manage object instances as well as supporting Hibernate access.  The part of the project I'm working on is headless so I would like to use a bootstrap classloader to help keep the installation process simple.  I would also like to use the TDSO infrastructure to share a few key objects.  Mixing the two ideas, however,  is proving to be a challenge.  As you may have guessed, part of Terracotta's magic is done via classloading which means you have play by their rules.  In my case, I'm creating a brand new loader for my application and not using any Terracotta classes.  Specifically, I'm creating a new URLClassLoader and populating it with the JARs and directories I need to run my application.  When I use the launcher in conjunction with TDSO, I get the following error:

"java.lang.IllegalStateException: This classloader instance has not been registered (loader"

A bit of Googling turns up a few discussions that suggest either writing a Terracotta Integration Module (TIM) or casting my loader to a NamedClassLoader and calling the __tc_setClassLoaderName method might solve my problem.  Writing a TIM seems like a lot of work but that is what was done for other environments that use custom classloaders, such as Tomcat and Jetty.  I put in some reflection code just to see if the __tc_setClassLoaderName was even available and, as expected, it was not.  I'm guessing because I never told TDSO to share the URLClassLoader so it didn't work any of its byte code manipulation magic.  This is going to be a tough nut to crack but I'm not ready to give up just yet.


  1. Any solution for this, yet. I am running into similar problem with Terracotta.

  2. Sorry, Tu, but I got moved over to another problem and never did discover the solution. The ideas I saw required casting to a Terracotta-specific class and invoking some of their APIs but never tested it out.