Extents of extensibility ("is this thing on?")

[David M. Lloyd]

Jigsaw still has one glaring hole in it which is a critical flaw: lack 
of extensibility.

There is no abstraction layer which would allow users to define their 
own module loading and definition scheme.  This is directly related to 
the way the module class loader, module, and module system APIs fit 
together.

Note that this is tied directly to the flawed notion of having a 
language-level construct for modules, which is ONLY done this way 
because of the murky "requirement" that modules be "part of the 
language".  As is often the case, this "feature" translates directly 
into a major constraint: it is impossible to achieve the above.

This requirement is senseless; I don't think more needs to be said, as 
the burden of justification lies with the requirement author.  By 
opening up module loading schemes to the user, the user can leverage the 
module system's (presumably) fast and powerful linking layer for their 
own plugin systems and containers - and this also "holds the door" open 
for a modular progression for Java EE, which is something, I might add, 
that we have already executed on with great success.

We have a ModuleLoader API [1] which provides for one-way delegation 
(think EE deployments delegating to the static boot module system), 
module unloading (but only for *your* module loader), and run-time 
module relinking, as well as being a touchstone for statistics and other 
run-time class loading management information.  We provide a default 
"boot" implementation which loads static module definitions off of the 
file system.

This API works *really well* for our uses and also allows users to 
create their own plugin schemes while still defining dependencies and 
filters in all the same ways that they would for static modules - which 
really stands to revolutionize how people write plugins.

Please consider abstracting module loading out into a separate API 
concept.  It is a good, solid approach.

[1] 
http://docs.jboss.org/jbossmodules/1.1.2.GA/api/index.html?org/jboss/modules/ModuleLoader.html
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- DML