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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