jcrinstall and OSGi start levels

[Bertrand Delacretaz <bd...@apache.org>]

Hi,

In my quest to make the installation/update/removal of bundles by
jcrinstall less asynchronous (see also SLING-733), I had a chat with
Felix and we talked about using OSGi start levels more systematically
in Sling, and especially in jcrinstall.

Here's a set of proposed changes to jcrinstall, comments are welcome.

1. The jcrinstall bundle is installed with a low start level (say 20),
lower than that of "application bundles"

2. Bundles installed by jcrinstall are set to a higher start level
(say 50), configurable in the jcrinstall service.

3. All initial bundle install/remove/update calls made by jcrinstall
happen in its activate() method

The goal is to make sure all bundle operations made by jcrinstall
happen before any of the bundles that it installs actually start -
that should help make the startup sequence more predictable.

Furthermore:

4. If the repository service goes away, jcrinstall brings the OSGi
framework's current start level down to its own start level (20 in our
example), and if possible (how?) makes sure all services that were
started at higher levels are stopped.

5. When the repository service comes back, the 1/2/3 rules above
apply, to make sure all bundle operations happen before bundles
installed by jcrinstall are started.

6. Once this is done, jcrinstall tells the OSGi framework to return to
the start level that was current before 4.

I'll hopefully start working on this next week.

-Bertrand