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Re: [equinox-dev] BundleContext and getName


yes and no.  Yes, the unique id of a bundle is in the manifest for that bundle.  There may be several bundles with the same unique id but different version numbers.  Each of these would have manifests with the the header
        Bundle-UniqueId: Foo  (or some such)
but
        Bundle-Version:
headers with different values

For some bundle Bar which can "see" a bundle Foo, the system will determine a particular version of Foo to present to Bar.  It is this Foo which Bar.getBundleContext().getBundle("Foo") should return.

So, to implement this using just getHeaders() you have to do something like
        Bundle[] bundles = Bar.getBundles()
        for each b in bundles
                String id= b.getHeaders().get("Bundle-UniqueId")
                if (id.equals("Foo"))
                        return b
        return null

Note that this only works if Bar.getBundles() returns only those bundles which Bar can see (as determined by the system).  Some have argued that this is an unacceptable semantic change.  That is, people expect getBundles() to return all installed bundles.  If it did that, then the list would include several Foo bundles and we would not know which one to pick.  Note that either way you cut it, the code above is slow.

Ultimately what is being discussed is the introduction of a semantically meaningful/powerful symbolic identifier for bundles that is independent of origin (location) and install circumstances (i.e., when it was installed).  This is in support of bundles as modules and other work where one bundle needs to refer to another bundle.  The argument is that this particular header is not "just another header" and it warrants concrete exposure on the API of Bundle/BundleContext.  Doing so allows for a clearer specification as well as easier, more efficient code.

Jeff




Benjamin Reed <breed@xxxxxxxxxxxxxxx>

10/07/2003 02:03 PM

       
        To:        Jeff McAffer/Ottawa/IBM@IBMCA
        cc:        equinox-dev@xxxxxxxxxxx, BJ Hargrave <hargrave@xxxxxxxxxx>, Pascal Rapicault/Ottawa/IBM@IBMCA, pkriens <Peter.Kriens@xxxxxxxx>
        Subject:        Re: [equinox-dev] BundleContext and getName



If the framework reconciles the view of each bundle, you still don't
have a problem searching headers. We have the same thing with
permissions and service registry -- the framework makes sure you only
see services that you are allowed to get.

If I understand correctly, everything you are trying to search on is
contained in the manifest. Right?

ben

Jeff McAffer wrote:

>
> I too am in favour of keeping the interfaces simple but there is a
> subtle point about function in question.  In the context of possible
> multiple version support, there may be several bundles with the same
> uniqueId but different version numbers.  One idea was that the
> framework would reconcile the view point of each bundle such that it
> "sees" at most one version of the bundles with any given unique-id.
>  Header lookup is not equivalent in this case.
>
> Jeff
>
>
>
>
> *Benjamin Reed <breed@xxxxxxxxxxxxxxx>*
> Sent by: equinox-dev-admin@xxxxxxxxxxx
>
> 10/06/2003 06:15 PM
>
>        
>         To:        pkriens <Peter.Kriens@xxxxxxxx>
>         cc:        Pascal Rapicault/Ottawa/IBM@IBMCA,
> equinox-dev@xxxxxxxxxxx, BJ Hargrave <hargrave@xxxxxxxxxx>
>         Subject:        Re: [equinox-dev] BundleContext and getName
>
>
>
>
> Actually Peter, the discussion was about getting a bundle from the
> location, not the name. They slipped another identifier in. Rather than
> proliferating methods I would encourage using Bundle.getHeaders() to get
> information about a specific bundle. If you want to add something to
> BundleContext, it would seem much better to do
> BundleContext.getBundles(Filter filter), where you can search on any of
> the header fields. That way when you find out that you want to look up a
> bundle by another manifest property (potentially Eclipse specific) you
> don't have to add another method.
>
> ben
>
> Peter Kriens wrote:
>
> >I saw the discussion regarding the extra method in BundleContext to
> >get a bundle from its name.

> >
> >We had this discussion in the past year in the OSGi and decided -not- to
> >extend the BundleContext interface to keep it as simple as possible.
> >There was quite a bit discussion about this.
> >
> >One thing that I proposed, which would more or less fit with the
> >existing standard, is to register the bundle objects in the registry
> >with properties for name, id, module, version, etc. This will allow
> >you search for bundles with an OSGi filter. This may be a cleaner
> >method than adding methods to BundleContext
> >
> >Kind regards,
> >
> >     Peter Kriens
> >
> >PR> Hi,
> >
> >PR> Currently BundleContext.getName(String) uses the Bundle-name
> entry to do
> >PR> the lookup.
> >PR> Now that we have Bundle-uniqueId, it seems to me that it would be
> more
> >PR> appropriate to do the lookup on this value.
> >PR> Any comments?
> >
> >PR>         PaScaL
> >
> >
> >  
> >
>
>
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