[jboss-as7-dev] Changed arguments…can we do better ? :P

[Andrew Dinn]

Hi Stuart,

On 02/01/2012 09:17 PM, Stuart Douglas wrote:
> Did you consider having byteman instrument the Class Loaders in the
> target vm, to always delegate to the system class loader if the class
> being loading starts with "org.byteman" ?
>
> I am pretty sure this is how JProfiler gets around the need for this
> setting.

I did consider this but I decided against it for two reasons:

1) the existing mechanism in JBoss modules already does the basic job of 
making Byteman classes available everywhere. So, duplicating it seemed 
inefficient both at devtime and at runtime.

2) doing the job properly will also involve adding exemptions for other, 
non-Byteman classes referenced at the point of injection and I am 
considering a better mechanism to make this work

To explain the latter, imagine that a rule injected into a JBossTS class 
needs access EJB types/methods. However, Byteman currently has to 
type-check and link the rule using the loader of the target class. So, 
you are snookered if the JTS module does not import the EJB classes.

I think I can get round this by adding i) module import statements to 
Byteman rule scripts ii) a plugin to the Byteman agent which resolves 
module imports and hands Byteman a multi-module loader for 
type-check/load, allowing rules to be linked against the union of the 
target module and the imported modules.

Of course the plugin and the import syntax would have to be module 
loader-specific.So, you would need an OSGI plugin, a JBoss Modules 
plugin, a Jigsaw plugin etc. But it should be easy to define a generic 
API for delegation of loader issues. So, watch this space.

regards,


Andrew Dinn
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