Re: [osgi-dev] Bundles importing and exporting the same package

Sat, 02 Aug 2008 13:25:42 -0700 

Alan Cabrera wrote:


On Aug 2, 2008, at 10:27 AM, BJ Hargrave wrote:



So we have:

foo:
Export-Package: a,b;uses=a
Import-Package: a

bar:
Import-Package: a, b

car:
Export-Package: a



Thus we have 2 exporters for a and one for b. Who ever imports should 
use the same a that foo uses.


So we can have


1) car exports a. foo exports a and b. bar import a and b from foo. 
 (No one uses a from car.)



2) car exports a. foo imports a from car and exports b. bar imports a 
from car and imports b from foo.



> bar can wire to foo's "b" and car's "a" package.  Won't that cause 
a problem?



This should not happen because of the uses constraint. This is the 
whole point of the uses constraint on the resolver. 



Let's say that foo and car are installed.  Foo gets resolved and uses 
its "a" export to satisfy its "a" import; car does not get used.



And so we're back to what 3.7 means by discarding the import.  If the 
import is discarded then there's no wire.  If there's no wire then 
there's no information to support the "uses" directive.  If there's no 
"uses" directive then there's no "uses" constraint.



Now bar gets wired.  There's no constraint to tell it to use foo and 
not car to wire "a".



You seem to think that "uses" only applies to a wire, but that is not 
the case. When a "uses" constraint is attached to an export, it is 
saying "if you import me and also import this package that I use, then 
we must both get the used package from the same provider." So, the 
provider could be another import or an export from the bundle itself, 
that doesn't matter, it just has to be the same provider.


-> richard




Regards,
Alan





--

*BJ Hargrave*
Senior Technical Staff Member, IBM
OSGi Fellow and CTO of the _OSGi Alliance_ <http://www.osgi.org/>_
[EMAIL PROTECTED] <mailto:[EMAIL PROTECTED]>      

office: +1 386 848 1781
mobile: +1 386 848 3788






From:   Alan Cabrera <[EMAIL PROTECTED] <mailto:[EMAIL PROTECTED]>>

To: 	OSGi Developer Mail List <[email protected] 
<mailto:[email protected]>>

Date:   2008/08/02 01:02 PM

Subject: 	Re: [osgi-dev] Bundles importing and exporting the same 
package



------------------------------------------------------------------------




On Aug 2, 2008, at 9:30 AM, BJ Hargrave wrote:



A bundle can either export OR import a given package name. A bundle's 
import is never resolved to its own export. There is mutual exclusion 
here.


So in your example one of 2 cases will occur:


1) the bundle will export a and b. Any classes within the bundle 
which want to use classes from a or b will use a and b from inside 
the bundle.


Let's call the previous bundle foo.  So, I have bundle bar:

Import-Package: a, b

and bundle car:

Export-Package: a


bar can wire to foo's "b" and car's "a" package.  Won't that cause a 
problem?



Regards,
Alan





2) the bundle will export b and import a. Any classes within the 
bundle which want to use classes from a will use the imported a. Any 
classes within the bundle which want to use classes from b will use b 
from inside the bundle.



The uses class for b (b; uses:=a) means that any bundle which import 
b (which does include the example bundle since it does not import b) 
should use the same a that the bundle from which b was imported uses. 
This should be quite easily met in your example.

--

*BJ Hargrave*
Senior Technical Staff Member, IBM
OSGi Fellow and CTO of the _OSGi Alliance_ <http://www.osgi.org/>_
[EMAIL PROTECTED] <mailto:[EMAIL PROTECTED]>      

office: +1 386 848 1781
mobile: +1 386 848 3788






From:   Alan Cabrera <[EMAIL PROTECTED] <mailto:[EMAIL PROTECTED]>>

To: 	OSGi Mail List Developer <[EMAIL PROTECTED] 
<mailto:[email protected]>>

Date:   2008/08/02 10:49 AM
Subject:        [osgi-dev] Bundles importing and exporting the same package



------------------------------------------------------------------------




If I read section 3.7. correctly, when an import gets resolved  
internally to its own export that overlapping import is discarded.  I  
take that to mean that the wire does not get created.  If I am correct  
then it seems that in certain cases, package constraints are not  
properly adhered to.


If we have a bundle:

Export-Package: a,b;uses=a
Import-Package: a


When the import of "a" gets resolved internally to its own export of  
"a", that overlapping import is discarded.  There's no wire to  
constrain users of package "b".


I may misunderstand something here.


Regards,
Alan

_______________________________________________
OSGi Developer Mail List_
[EMAIL PROTECTED] <mailto:[email protected]>_
__https://mail.osgi.org/mailman/listinfo/osgi-dev_

_______________________________________________
OSGi Developer Mail List_
[EMAIL PROTECTED] <mailto:[email protected]>_
__https://mail.osgi.org/mailman/listinfo/osgi-dev_
_______________________________________________
OSGi Developer Mail List
[email protected] <mailto:[email protected]>
https://mail.osgi.org/mailman/listinfo/osgi-dev
_______________________________________________
OSGi Developer Mail List
[email protected] <mailto:[email protected]>
https://mail.osgi.org/mailman/listinfo/osgi-dev


------------------------------------------------------------------------

_______________________________________________
OSGi Developer Mail List
[email protected]
https://mail.osgi.org/mailman/listinfo/osgi-dev

_______________________________________________
OSGi Developer Mail List
[email protected]
https://mail.osgi.org/mailman/listinfo/osgi-dev






















					Reply via email to