Device Access service

[David Lindelöf <da...@adhoco.com>]

Dear all,

Can someone help me shed light on the Device Access service? There are a
couple of things I do not understand:

1) P. 50-51 of the OSGi Service Compendium R4 gives a example of a
driver for a "WidgetDevice" device service. The code of the
SerialWidgetDriver class seems to imply that before this class is
instantiated, someone else has already registered a WidgetDevice
service. Who is this someone else?

2) How does the implementation of the WidgetDevice service "know" which
driver to use? The SerialWidgetDriver.attach() method takes a
ServiceReference as an argument, so there is no way for the driver to
tell (say) WidgetServiceImpl "hi, you can use me to access the serial
port now". All I see is that the SerialWidget class provides a serial
access service to any bundle in the framework, not just to
WidgetServiceImpl.

This is odd because it seems to imply that even though
SerialWidgetDriver.attach() has been succesfully called,
WidgetServiceImpl must still on his own discover a serial access service
that it can use.

3) On p. 50, will the addingService() method be called upon
instantiation, even though the WidgetDevice service is already
registered (usually) when SerialWidget is instantiated?

I mean, this is the normal chain of events as I understand it:

- The Force registers a WidgetDevice service with its implementation
WidgetServiceImpl.

- The DriverLocator finds the SerialWidgetDriver, installs it, matches
it against WidgetDevice, and calls the attach() method with a service
reference to WidgetDevice as argument.

- SerialWidget is instantiated, passing a service reference to
WidgetDevice to its parent's (ServiceTracker) constructor.

- Since WidgetDevice is already registered, nothing else happens and
addingService() is not called. And no serial access service is
registered by SerialWidget. WidgetDeviceImpl is left hanging in memory
space.


I'd really appreciate any help some kind soul could offer me on this
topic.

--
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David Lindelöf
Product Developer
Adhoco AG
Technopark
Jagerstrasse 2
8406 Winterhur
tel +41-52-203.2903
mob +41-79-415.6641
fax +41-52-203.2904
e-mail david.lindelof@adhoco.com
url http://www.adhoco.com
weblog http://visnet.ch/smartbuildings/
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