Potential fix: Running configurations not saved on shutdown

[Tom McQueeney <to...@mcqueeney.com>]

For GERONIMO-657, Running configurations not saved on shutdown 
(http://issues.apache.org/jira/browse/GERONIMO-657), I have a potential 
solution I'd like to run by those interested.

The shutdown hook for FileConfigurationList doesn't run because it gets 
unregistered during the kernel shutdown process. The 
ConfigurationManagerImpl shutdown hook gets run first, knocking the feet 
out from under any other shutdown hook registered by another GBean. This 
hook tells all loaded configurations to stop. Thus, when the 
FileConfigurationList gets the doStop(), it dutifully unregisters it 
shutdown hook to save the active configurations. The 
FileConfigurationList hook never runs.

One way to solve this problem is to ensure the ConfigurationManagerImpl 
shutdown hook runs last. To do this, we could define a shutdown hook 
ordering, such as adding a "priority" parameter to the Kernel's 
registerShutdownHook method. Something like:

     /**
      * Registers a runnable to execute when the kernel is shutdown
      * @param hook a runnable to execute when the kernel is shutdown
      */
     void registerShutdownHook(Runnable hook, int priority);

Using an int would be a quick way, and we could define two priorities, 
LOW and HIGH and ensure the ConfigurationManagerImpl uses LOW. Or we 
could use an enumerated priority object type. Either way isn't terribly 
clean because a GBean registering a shutdown hook has to have a good 
idea of what order its hook should run, and really we only need to 
assure that stopping all configurations is performed last rather than 
needing the other shutdown hooks to run first.

Perhaps a better solution would be to add a boolean "runLast" parameter 
instead of a priority parameter. A true param would mean add the hook to 
the end of the shutdown hook list, while those with false would be added 
to the front.

I'd be happy to implement a solution like this if folks think it's a 
good idea.

-Tom