Re: [equinox-dev] .qualifier for export package?

[John Arthorne <John_Arthorne@xxxxxxxxxx>]

Good to know. I guess it was a bit too
dogmatic to suggest import-package is only useful for spec-level dependencies
that avoid any implementation-level dependency. I suspect this case of
standard non-interchangeable packages that roam between different bundles
is not very common though.

John

Thomas Watson <tjwatson@xxxxxxxxxx>
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09/09/2008 09:16 AM

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Subject	Re: [equinox-dev] .qualifier for export package?

The ServiceTracker is a class provided by OSGi and is
common. It does not have to be packages with the Framework (like we do
in Equinox) it can be packages and exported from any bundle.

Tom

John
Arthorne ---09/08/2008 11:53:37 PM---Wouldn't importing a micro version
cause the client to be stuck with one particular implementation of ServiceTracker
and preven

From:	John Arthorne <John_Arthorne@xxxxxxxxxx>
To:	Equinox development mailing list <equinox-dev@xxxxxxxxxxx>
Date:	09/08/2008 11:53 PM
Subject:	Re: [equinox-dev] .qualifier for export package?

---

Wouldn't importing a micro version cause the client to be stuck with one
particular implementation of ServiceTracker and prevent replacing with
another implementation (which might not have the same bug or have a different
micro version)? Or is this particular class an implementation that is provided
by the OSGi alliance and is common across frameworks?

Thomas Watson <tjwatson@xxxxxxxxxx>
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09/05/2008 01:13 PM

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Subject	Re: [equinox-dev] .qualifier for export package?

For the most part I agree. But I do think there is value in versioning
API packages that contain not only pure specification but also implementation.
One real example is the OSGi package org.osgi.util.tracker package. This
package contains the ServiceTracker API, but the ServiceTracker class also
provides a significant amount of code behind the implementation of the
API. Any bug fixes to the implementation contained in this package should
be reflected by increasing the micro version of the package. Clients that
only care about the pure specification would use the major.minor version
to import, but if a bundle cannot work without some fix contained in a
micro version of the package then the bundle should be able to import down
to the micro version of the package.

Tom

John
Arthorne ---09/05/2008 11:00:08 AM---We have qualifiers on bundles to support
the notion of provisioning "line-ups" (aka features) that list
precise groups of IUs (

From:	John Arthorne <John_Arthorne@xxxxxxxxxx>
To:	Equinox development mailing list <equinox-dev@xxxxxxxxxxx>
Date:	09/05/2008 11:00 AM
Subject:	Re: [equinox-dev] .qualifier for export package?

---

We have qualifiers on bundles to support the notion of provisioning "line-ups"
(aka features) that list precise groups of IUs (one precise build of a
particular bundle). We *don't* have qualifiers on bundles so that require-bundle
statements can precisely choose a particular build of a bundle to depend
on, since this kind of coupling is too restrictive. We don't have any mechanism
today for defining line-ups of packages as we do today with bundles, so
qualifiers on packages currently have no value. 

I think the use case you have in mind is picking a single bundle as a starting
point, and then expanding from that bundle based on its dependencies (picking
a thread in the ball of yarn and pulling on it to see what comes out).
In this scenario, if the bundle has an import-package statement, and there
are multiple builds of a bundle providing that package in the repository,
which one do you choose? The problem here as BJ points out, is we would
never want to couple our require-bundle/import-package statements down
to the qualifier level. This tight coupling completely defeats the purpose
of the component architecture where dependencies are expressed at the level
of specification. So, I don't think this ball-of-yarn scenario can work
in a development scenario where I want to provision and test a particular
build from a development repository containing several builds. I think
this scenario is only interesting when run against repositories of officially
released content such as the release train repository, in which case any
package that satisfies the import is acceptable and qualifiers on either
imports or exports are not needed. 

More fundamentally, I may be alone here but I question the premise that
packages are simply finer-grained versions of bundles, and so everything
we do with bundle versions is still applicable at the package level. My
thinking is that a bundle is a container that holds specifications, implementations,
and other non-code artifacts. As such its version number must have the
flexibility to capture the fact that it contains not only API, but other
non-API artifacts that people may rely on (implementation characteristics,
extension points, documentation, source code, etc). When someone has a
require-bundle statement, they may want to express their dependency on
any one of the things that bundle contains. Thus it's reasonable for someone
to have a dependency range of, say, [1.0.2,2.0.0) on a bundle, because
they may rely on some non-code attribute of the bundle that was introduced
in version 1.0.2. 

An API package, on the other hand, is pure specification. Version numbers
on packages can thus be expressed purely as a function of the API in the
package. If the API changes, the version changes, if the API doesn't change,
the version doesn't change. I don't even see a need for the service segment
on a package: major.minor should be enough to express compatible and incompatible
API changes. In my view the only value of the push towards import-package
is it moves dependencies from the container (bundle), to the specification
(package). It is not simply a push towards dependency on finer-grained
containers (which can be acheived simply by making our bundles smaller).
The great power of this shift is that it allows for the flexibility of
interchangeable implementations of that specification. Moving to this world
means you can no longer rely on non-API characteristics of a package, so
having an import-package define more than a major.minor dependency defeats
the purpose. 

I think we need to make sure we agree on *why* moving from require-bundle
to import-package is valuable. That will held guide our thinking on the
semantics of package version numbers, where to use them, and the related
use cases around them. I would argue that today only a very small number
of Eclipse API packages are truly pure specification that one could reasonably
swap out the implementation of transparently. In my view these are the
only packages that are worth versioning at the package level. I certainly
think the *goal* should be moving towards this world of specification-level
dependencies (and thus use of import-package), but that's not where we
are today. 

John

Jeff McAffer <jeff@xxxxxxxxx>
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09/05/2008 01:33 AM

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Subject	Re: [equinox-dev] .qualifier for export package?

I'm certainly sympathetic to you thinking here. Having qualifiers in import
statements is ugly at best. The challenge is that in the dev cycle the
API of something may change many many times. This would lead to quite visible
changes in unreasonable ways. For example, say we introduce some API and
then "break" it several times as we refine in the dev cycle.
Then the first release of the API might have version 42.23.27 or some such.
Trying to manage API semantics during the dev/release cycle seems like
overkill. Clearly that is an over done example but you get the point I
hope.

Lets step back for a second. Some goals in decreasing order of priority/importance.

Goal #1: ensure that at least all API packages have version numbers on
the exports.
Goal #2: be able to eat our own dog food wrt provisioning and version management
during the dev cycle.

Good news is that #1 is likely agreed to and *all* we have to do is put
the initial version numbers on the current packages and then have the tooling
help people manage them according to the current versioning model.

The proposal for using .qualifier was actually one possible implementation
of goal #2. #2 is interesting because eating our own dog food seems to
greatly increase the likelihood of our technology being good/useful. Without
some sort of increasing version number on the packages, p2 for example,
will have a hard time figuring out what to give you cause everything will
look the same to it.
Can anyone think of another way of enabling #2? Of the top of my head I'm
thinking that something like the odd/even version pattern might help...

Jeff
BJ Hargrave wrote: 

If you change API during dev cycle, that is the proper time to also change
the major or minor version. That is the whole point. I would assume that
API tooling will complain until you do so. Just changing the qualifier
is insufficient to capture an API change. Also, I think that last thing
we want to see are bundles using qualifiers in import package statements!
So if you use qualifier to denote API change during dev, then other bundles
will need to import using qualifiers to ensure they wire to the desire
API if they use it. UGLY! 

Qualifiers are useful to capture implementation changes. But API is a specified
thing that changes deliberately and (hopefully) slowly and its version
is not subject to implementation. 
--

BJ Hargrave Senior Technical Staff Member, IBM OSGi Fellow and CTO of the OSGi Alliance hargrave@xxxxxxxxxx

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

From:	Jeff McAffer <jeff@xxxxxxxxx>
To:	Equinox development mailing list <equinox-dev@xxxxxxxxxxx>
Date:	2008/09/03 06:16 AM
Subject:	Re: [equinox-dev] .qualifier for export package?

---

I understand your hestiation and actually agree with you from the "released
code" point of view. However, we spend a lot of time dealing with
code and API that is in development. If we are to have any hope of provisioning
and managing that, we need to know the difference between the various iterations
of the packages. For example, when someone adds an API during the dev cycle
and you want use it, you need to import the right version of the package
to ensure you get it. Changing the first three segments version number
of the package for every change done in the dev cycle feels too disruptive.

To a certain extent this could be handled in the provisioning system but
that would force the situation of bundles in a particular context (e.g.,
a build "lineup"). That is, bundles would no longer be completely/accurately
self-describing.

Jeff

BJ Hargrave wrote: 

I would be extremely cautious about using qualifier on package versions.
I must say that I have never seen it done. 

It seems an over specification. I think that having build tools to advise
you to increment the micro is more than sufficient.
--

BJ Hargrave Senior Technical Staff Member, IBM OSGi Fellow and CTO of the OSGi Alliance hargrave@xxxxxxxxxx

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

From:	Thomas Watson/Austin/IBM@IBMUS
To:	Equinox development mailing list <equinox-dev@xxxxxxxxxxx>
Date:	2008/09/02 10:45 AM
Subject:	Re: [equinox-dev] .qualifier for export package?

---

Before recommending every package uses a qualifier I have the following
concerns:

1) In Eclipse we have loads of packages. We better make sure all identical
qualifier Strings are shared (interned etc.) for performance reasons. Today
when loading from a cached state we share identical Version objects. Because
package versions are managed independently we will end up with lots of
different versions that have the same qualifier exported by a bundle. We
also will limit the ability to share Version objects across bundles because
each will use a different qualifier (unless we happen to use the same CVS
tag).

2) The qualifier will change even in cases where no code was touched in
the package. I'm not sure this is a valid concern. The code got recompiled
so perhaps changing the version qualifier is warranted. But we need to
think about the consequences. For example, I can see API tooling start
to complain that the micro version of a package should be increased to
indicate a bug "fix" when comparing the package versions with
a base line. It will notice that the qualifier changed from a previous
release but the micro version was not increased.

3) What about versions of packages which we do not maintain the API for
at Eclipse. Things like org.osgi.* and orbit bundles. Shouldn't we use
the version the producers of the API have defined? Adding a qualifier here
does not seem right, especially if a qualifier is already defined by the
producers.

On the surface this sounds like a fine idea, and I am not completely against
it. But I would like to take the first step of versioning the Eclipse API
packages first to see what all the issues are with independent package
versioning. I'm sure we will run into other hurdles along the way. For
example, how does a developer maintain the version of a split package across
all the bundles the package is split?

Tom

"Chris
Aniszczyk" ---08/31/2008 02:46:34 PM---On Sun, Aug 31, 2008 at 5:53
AM, Jeff McAffer < jeff@xxxxxxxxx

From:	"Chris Aniszczyk" <caniszczyk@xxxxxxxxx>
To:	"Equinox development mailing list" <equinox-dev@xxxxxxxxxxx>
Date:	08/31/2008 02:46 PM
Subject:	Re: [equinox-dev] .qualifier for export package?

---

On Sun, Aug 31, 2008 at 5:53 AM, Jeff McAffer <jeff@xxxxxxxxx>
wrote: 
As version numbers on packages become more prevalent does it start making
sense to use .qualifier on them in addition to bundle version numbers?
The logic here is the same as for bundles. we rev the version number of
the bundle to match the most extreme change for that release. in between
if hte provisioning system is going to do its job, it needs to have different
version numbers. Teh .qualifier allows for the auto-qualification of bundle
version numbers. The same is true for folks using import/export package.

+1

In PDE, I plan on releasing some builder logic to flag exported packages
without versions with a warning in M2. API Tooling also has items in plan
that deal with package versioning, but that will be post M2

Thoughts for how/if this should be introduced? 

I say before M2, we formulate a plan across the Eclipse proper projects
to deal with versions on package exports. We can than look at pushing that
plan to other Eclipse.org projects as a best practice once we get the hang
of it.

-- 
Cheers,

~ Chris Aniszczyk_______________________________________________
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