Re: [orbit-dev] Status of "uses" directive in Equinox and Orbit bundles

[Christian Damus <cdamus@xxxxxxxxxx>]

Hi, Tom,

I'll find a way to get my set-up to you.  Thanks!

On the subject of re-exports:  I thought Eclipse's recommendation was
always to re-export dependencies whose types comprise part of a bundle's
API (as in "uses").  Say I have:

   Bundle A
       - package a
         - class X extends b.T
            - public b.U getU()
       - MANIFEST.MF
          - Export-Package: a
          - Require-Bundle: B

   Bundle B
       - package b
         - class T
         - interface U
       - MANIFEST.MF
          - Export-Package: b

I thought the general recommendation was that A should re-export B to
ensure that users of the "a" package A don't have to specify a version
tolerance on A if they only use the "a" package via "b."  Otherwise, if
they independently specify a dependency on A (or "a"), then they have to
keep the version tolerance in sync with B's dependency on A (or "a").
Moreover, when B later adds a dependency to bundle C with package "c" and
exposes types from "c" in its API, then users of B will have to add their
own dependencies on C (or "c") even if they don't know that they are using
B's APIs that use "c" (perhaps via reflection?).

Maybe much of this thinking is pre-OSGi/Equinox and needs to be updated?  I
know that on the project I work on, the rule that a bundle whose API is
surfaced in a dependent's API must be re-exported by that dependent is
applied absolutely.

Cheers,

Christian




Christian W. Damus
Component Lead, Eclipse OCL and EMF MQ/MT/VF
IBM Rational Sofware


                                                                           
             Thomas Watson                                                 
             <tjwatson@xxxxxx.                                             
             com>                                                       To 
             Sent by:                  Orbit Developer discussion          
             orbit-dev-bounces         <orbit-dev@xxxxxxxxxxx>             
             @eclipse.org                                               cc 
                                                                           
                                                                   Subject 
             01/04/2008 05:18          Re: [orbit-dev] Status of "uses"    
             PM                        directive in Equinox      and       
                                       Orbit   bundles                     
                                                                           
             Please respond to                                             
              Orbit Developer                                              
                discussion                                                 
             <orbit-dev@eclips                                             
                  e.org>                                                   
                                                                           
                                                                           




> Thanks, Tom,
>
> The product in which this problem came up is reasonably large (> 1000
> bundles).  Moreover, there are more than a dozen bundles within Batik
that
> all "use" each other.  It's a tangled web.  :-)   Perhaps, then, I shall
> try to re-introduce the "uses" in my bundles and beg you for help if I
run
> into difficulties.

OK, Please let me know if I can get access to your setup once you have
something available.  I would like to have a look to make sure the
situation
has a relatively large and complex number of solution sets which for which
the resolver must select an answer from.  Unfortunately we are dealing
with an NP-Complete problem for which some situations will be solved very
quickly while others can take an exponential amount of time to solve.

>
> I have another question, not quite related.  I have discovered, I think,
> that whereas I can re-export API of a bundle dependency using the
> "visibility=reexport" directive in a Require-Bundle header, it is not
> possible to Export-Package a package that was Import-Packaged in order to
> re-export it (PDE flags it as an erroneous attempt to export a package
not
> defined in the bundle).  Is there a way to re-export packages obtained
via
> Import-Package?

No, you cannot reexport packages you get from Import-Package and I really
do
not like the visibility=reexport approach either.  To me this is just a way

to make our clients very lazy in their constraint definitions.  Just
because
someone requires you does not always mean that they will need access to
some
bundle you require.  The visibility=reexport option only makes the
transitive closure of your dependency graph that much more complex.  It
becomes much more difficult to look at a bundle's manifest and see where it

gets its external classes from.

OSGi does allow you to "reexport" a package from one of your required
bundles
though.  For example, suppose bundle A required bundle B and bundle B
exports
the b.foo.bar package along with a whole bunch of other b.* packages.  In
A would like reexport the b.foo.bar package to other bundles that require
bundle A but not all the other b.* packages.  In this case you would use
the
following in bundle A

Bundle-Symbolic-Name: A
Require-Bundle: B
Export-Package: b.foo.bar

This is perfectly ok in OSGi, but I expect PDE will flag a warning/error
that
you are exporting a package not included in your bundle.  You can safely
ignore this error/warning.  Personally I do not really mind the error
though
because I really do not think reexporting packages or required bundles is a

good thing :)  To me all clients should clearly define their requirements
and
additional requirements should not be induced on a client through a
constraint
on a bundle (i.e. Require-Bundle).

>
> Thanks for your help!
>
> Christian
>
>
>
>
> Christian W. Damus
> Component Lead, Eclipse OCL and EMF MQ/MT/VF
> IBM Rational Sofware
>
> _______________________________________________
orbit-dev mailing list
orbit-dev@xxxxxxxxxxx
https://dev.eclipse.org/mailman/listinfo/orbit-dev