Review request on the optional modules support

[Sean Mullan]

Hi Mandy,

I was just reviewing the design note (not the webrev) and I had a couple of
minor comments -

Optional Module

first sentence, suggest:

s/referred as optional module/referred to as the optional module

2. ModuleNotPresentException

"if it's absent, a ModuleNotPresentException as in the "foo" module example
given above."

I could not find the "foo" module example above. Do you mean the one at the end
of the document?

JDK Optional Dependenceies
1. APIs that throw ModuleNotPresentException

Are those really the only APIs that require optional modules? Aren't there also
internal APIs that have optional dependencies? Don't they need to be updated as
well?

General Question

I'm not sure if this question makes sense, but what happens in the future if
JAXP is required by the base module? Would it still make sense to annotate APIs
in the module that require it as an optional module?

--Sean


On 8/4/11 3:35 PM, Mandy Chung wrote:
> An update on the optional module support [1].
> 
> Webrev: 
> http://cr.openjdk.java.net/~mchung/jigsaw/webrevs/optional-modules.00/
> 
> The note has been updated to include the open questions raised in the
> discussion. http://openjdk.java.net/projects/jigsaw/doc/topics/optional.html
> 
> There is an open question whether the isModulePresent method should take a
> version-range argument or other alternative for an application to support
> different versions of modules with incompatible change (see [2]).
> 
> I propose to get this prototype in the jigsaw repository first and address
> the open question next as we would need to get the use cases to determine
> what the right API for it.
> 
> Summary of Changes: 1. A new @RequireOptionalModule annotation is defined to 
> indicate that the annotated type requires the optional module to be present
> when it's referenced; otherwise, ModuleNotPresentException would be thrown.
> 
> See java.util.Properties.loadFromXML and other examples in the JDK.
> 
> 2. Two new methods are added in the java.lang.reflect.Module class to test if
> a module has been resolved and linked with this module's context.
> 
> The requireModulePresent(String mn) method checks if the given module is
> present; if not, it throws ModuleNotPresentException.
> 
> isModulePresent(String mn) simply returns true/false and it can be used for
> the fall-back cases if an optioanl module is not present.
> 
> 3. Class.getModule() is modified to lazily set the Module for a system class
> loaded by the VM bootstrap null loader.
> 
> The VM loads the primordial classes directly in the VM and also other system
> classes when the caller is loaded by null class loader without calling the
> library. The Class's module field is null in that case.  The Loader class is
> refactored to support the lazily initialization of the Class's module.
> 
> 4. An optional module that doesn't any local class but just reexports another
> module is not currently stored in the configuration.  Thus the loader can't
> find it even if it's present. jdk.jaxp is an example that reexports sun.jaxp 
> as sun.jaxp exports its internal APIs and permits only specific module to use
> (jaxws) while jdk.jaxp only reexports the public APIs.
> 
> I simply added the remote contexts list in the configuration as the fast
> configuration work will further change the layout. With another change I made
> in the SimpleLibrary.StoredConfiguration class to add indirection for the
> context name that reduces the config file size [3], the remote contexts list
> should have minimal impact to the config size.
> 
> Please also note that I added a "Guideline of Using Optional module" section
> in [2] which is intended to illustrate the class loading issue with optional
> module but not as a recommendation for the coding practice. This would be
> another topic to discuss.
> 
> Thanks Mandy
> 
> [1] http://mail.openjdk.java.net/pipermail/jigsaw-dev/2011-May/001298.html 
> [2] http://openjdk.java.net/projects/jigsaw/doc/topics/optional.html [3]
> http://mail.openjdk.java.net/pipermail/jigsaw-dev/2011-June/001349.html