There is a snag with this approach. Imagine your bundle and the
CM implementation has a start-level of 4 and that the framework
is launched with a beginning start-level of 3. At launch the
system bundle will be in the STARTING state until the start-
level 3 has been reached. At that point the FrameworkEvent
STARTED will have been fired and the system bundle will be
ACTIVE. Later if someone raises the start-level to 10 your
bundle will be allowed to activate along with the CM
implementation but the order may be such that your bundle is
activated before the CM implementation.
During your bundle's activation the system bundle will be ACTIVE
but there will be no CM service available yet. You could try to
listen for the STARTLEVEL_CHANGED event, but you have no idea if
your bundle is being activated because of a start-level change
or simply because someone called start on your bundle. The other
issue with this approach is that there is no guarantee that the
CM implementation bundle will synchronously register its service
during its activation. Even after the FrameworkEvent (STARTED or
STARTLEVEL_CHANGED) event has been fired there may be some
asynchronous operation going on that will eventually cause the
CM service implementation to be registered.
The only safe way I can see to do this is to always register
your ManagedService, if your ManagedService was not called with
a configuration (or null for no configuration) during the
registration of the ManagedService then you must apply your
defaults. This may introduce some quick churn between your
defaults and an actual configuration if the CM implementation is
registered after you have registered your ManagedService but I
see no safe/elegant way around that.
Tom
Inactive hide details for BJ Hargrave---11/13/2009 09:56:20 AM---
If you optionally import the cm package and don't "get it" wheBJ
Hargrave---11/13/2009 09:56:20 AM---If you optionally import the
cm package and don't "get it" when you resolve, then you will
never see CA, so just use the defaul
From: BJ Hargrave/Austin/i...@ibmus
To: OSGi Developer Mail List <[email protected]>
Date: 11/13/2009 09:56 AM
Subject: Re: [osgi-dev] How to reliably detect that
Configuration Admin is *not* present?
------------------------------------------------------------------------
If you optionally import the cm package and don't "get it" when
you resolve, then you will never see CA, so just use the defaults.
If you get the cm package, register your MS. Then look to see of
the CA service is registered. If it is, then just wait for the
call to your MS. If the CA service is not registered, then
immediately use your default. Then later if CA is started, you
will get called at your MS and you can then move to use the
configuration (if any).
If you get started before CA during framework launch, then you
may end up using your defaults for a brief period before you get
called at your MS. You can compensate for this by looking at the
state of the system bundle (during your activator). If the
system bundle state is STARTING, the framework is launching.
Register a FrameworkListener and wait for the STARTED event
which tells you launch is complete. If you haven't been called
at your MS by then, then there is likely no CA service.
--
*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: David Bosschaert <[email protected]>
To: OSGi Developer Mail List <[email protected]>
Date: 2009/11/13 10:29
Subject: Re: [osgi-dev] How to reliably detect that
Configuration Admin is *not* present?
Sent by: [email protected]
------------------------------------------------------------------------
Hi all,
Thanks for the feedback. Sorry that I didn't formulate my question
precise enough.
I got things working with a separate class that implements the
ManagedService which only gets used if the class is there
available
(optional cm import).
The main question I'm still a little struggeling with is: how
long do I
wait. As Per says, if the CA service is present I will get
called with
updated() no matter what. But how long do I wait before deciding
that
the CA service is not present? Especially during startup this
could
depend on the bundle ordering and considering the machine
capabilities
and the number of bundles this could take either a long time or
a fairly
short amount of time. I'm not particularly a fan of arbitrary
timeouts
so I was thinking is there some other mechanism? I also don't
want to
use the defaults if typically in the next second the real values
become
available...
Maybe something like this:
* every second look at all the installed bundles
(BundleContext.getBundles())
* if this information doesn't change (no extra bundles and all the
bundles remain in their previous state) assume that the system has
started up
* now check whether the CA service is there, if not use the
defaults...
Or would using the StartLevel service be an alternative? Or does
that
merely move the problem?
David
Per Gustafson wrote:
> I think the general approach BJ describes is good. But in case
(2) the
> MS will get called with a null dictionary (see 104.5.3 of the
> Compendium spec) so you don't have to bother with a timeout.
>
> /Per
>
> On Nov 13, 2009, at 08:36 AM, BJ Hargrave wrote:
>
>> I think your question is: How long do I wait for my
ManagedService to
>> be called with my configuration before I decide I need to use
some
>> defaults?
>>
>> There are 2 reasons why your MS may not get called. (1) There
is no
>> ConfigAdmin running (yet). (2) Your MS does not have a
configuration.
>>
>> (1) Can be detected because there is no ConfigAdmin service
>> registered. If this is the case, use your defaults but still
register
>> the MS because the ConfigAdmin service may get started shortly.
>>
>> (2) If there is a ConfigAdmin service, then you may want some
timeout
>> before you give up waiting for some configuration and using
your
>> defaults. In this case still leave your MS registered.
>>
>> In all cases, register the MS and respond to update.
>> --
>> BJ Hargrave
>> Senior Technical Staff Member, IBM
>> OSGi Fellow and CTO of the OSGi Alliance
>> [email protected]
>>
>> office: +1 386 848 1781
>> mobile: +1 386 848 3788
>>
>>
>>
>> From:
>> David Bosschaert <[email protected]>
>> To:
>> OSGi Developer Mail List <[email protected]>
>> Date:
>> 2009/11/12 23:22
>> Subject:
>> [osgi-dev] How to reliably detect that Configuration Admin is
>> *not* present?
>> Sent by:
>> [email protected]
>>
>>
>>
>>
>>
>> Hi all,
>>
>> I have a bundle that can be configured through Configuration
Admin.
>> However when CA is *not* present it can still function using
default
>> behaviour.
>>
>> Question 1: What would be the best way to let it check that the
>> Configuration Admin service is not present, so that it can
proceed with
>> its default behaviour?
>>
>> Question 2: I would really like it to have an *optional*
dependency on
>> org.osgi.service.cm. but still my code provides a class that
implements
>> org.osgi.service.cm.ManagedService I guess this should be
possible,
>> right? I was thinking of the following algorithm:
>>
>> If Not Config Admin Present then
>> default behaviour
>> else
>> register MyManagedService // only at this point the
ManagedService
>> class gets loaded
>> ... handle configuration as soon as updated() gets called.
>>
>> Is this a feasible approach?
>>
>> Thanks,
>>
>> David
>>
>>
>> _______________________________________________
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>> OSGi Developer Mail List
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>
> _______________________________________________
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>
>
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