uses is useless ?

[forax at univ-mlv.fr]

----- Mail original -----
> De: "Alan Bateman" <Alan.Bateman at oracle.com>
> À: forax at univ-mlv.fr
> Cc: "jigsaw-dev" <jigsaw-dev at openjdk.java.net>
> Envoyé: Mercredi 16 Novembre 2016 11:44:21
> Objet: Re: uses is useless ?

> On 16/11/2016 10:25, forax at univ-mlv.fr wrote:
> 
>> :
>> The whole point of uses is to enable a kind of static analysis on the service
>> dependencies,
>> if 'uses' is not required, if you can easily bypass it or it doesn't provide
>> useful information,
>> then it should be removed from the spec.
> `uses` is used to link the consumers of services to the providers of
> services. If nobody `uses S` then the modules that `provides S with ...`
> will not be resolved (assuming nobody directly depends on these service
> provider modules).

My point is that in teory, that's cool but in reality the module-info of java.base (or java.sql) declares a lot of 'uses' making the whole idea moot.
To avoid java.base to use 'uses', we need a way to be able to have a way to delegate the power of the ServiceLoader to another code, so the other code will have to use 'uses'.

> 
> The scenario where a framework uses ServiceLoader on behalf of a
> consumer really needs the consumer to declare that it uses the service
> type, otherwise there is no guarantee that the modules that provide
> implementation of the service will be resolved.

yes !
if a class calls DriverManager.drivers(), 'uses' should be defined on the module of the class and not on the module of DriverManager, as this is currently the case.

Rémi

> 
>> :
>> Yes, jlink doesn't do that, but my tool on top of jlink does it :)
>> But as i said above, if the information given by 'uses' do not allow to do
>> static analysis like finding the root modules (services included), it perhaps
>> means that 'uses' doesn't worth its own weight.
> jlink could do service binding
> (s/resolveRequires/resolveRequiresAndUses) but all the initial feedback
> was that people wanted the minimum number of modules in the image. It's
> not hard to have jlink make some suggestions, it just hasn't been
> implemented (this is what the open issue in JEP 282 is about).
> 
> -Alan