Re: [equinox-dev] Creating and Starting a BundleActivator when the frame

[Jeff McAffer <Jeff_McAffer@xxxxxxxxxx>]

Gee, take a day off reading the list
and all sorts of interesting stuff goes on... ;-)

As Neil pointed out, there certainly
are quite a number of people doing quite different things with Equinox
so all these kinds of discussions are good.

A coarser version of the approach Neil
outlines is taken by some products.  They just have a starter bundle
that starts everything.  We have debated adding an agressive start
option to the framework as a whole but to date have not done it.  In
fact, I suspect that the reason you have never had this problem is that
the framework you have been using (SMF) did in fact automatically start
every bundle on installation.  The specification (AFAIK) completely
stays away from this sort of discussion and defers to some sort of external
agent that is managing the system.

Which leads us to BJ's suggestion of
having Update Manager (i.e., some external management agent) know/be told
to start bundles as it installs them.  This too is a fine idea and
should be looked at for 3.3.  The interesting thing about this approach
(and I think Neil or BJ pointed it out) is the point of view.  History
has shown us that producers of bundles have considerably different views
of the importance of their function than that of consumers.  Many
producers believe it is absolutely critical that their function be agressively
installed and started and active and loaded and initialized and...  Of
course, consumers are composing many of these bundles and quite often don't
want any of that.  So the update manager (and similar) approach puts
the power in the hands of the consumer as they can design features to meet
their needs and those of their users.  

A tweak on this that combines the approaches
is to allow for overriding bundle metadata.  The idea here is to allow
say features to include new bundle manifest data for the bundles it lists
(potentially indirectly).  This way the consumer can consume features
(what they are really interested in) without modification but somewhere
above define some overrides that cause various bundles to be started.

The solution proposed below provides
an "out" if a producer adds the "ImmediateActivation"
header and the consumer doesn't want it.  By not installing the starter
bundle (X in the example) this action can be ignored.  However, if
you want some but not all started or the bundle producer did not include
the ImmediateActivation header, you are not as happy.

BTW, at some point in the discussion
you (Simon) mentioned the disparity between the Eclipse Application and
Equinox Framework launch configurations.  Yes, this can be off-putting
and I suspect that as we improve the OSGi-ness of the application and programming
models, these two notions will get better aligned.  In the mean time,
you are free to use the Equinox Framework launch configuration to start
an Eclipse Application.  You just have to ensure that the Runtime
bundle and it prereqs are set at the right start level and started (see
the config.ini for you standard Eclipse) and the other bundles you want
are also setup to start or not as you choose.  The point of the Eclipse
Application launch config is to simplify the workflow for a specific class
of developers.  In the end, lauching Eclipse is just launching Equinox
in a specific way.

Jeff

"Neil Bartlett" <neil@xxxxxxxxxxxxxx>
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04/09/2006 08:56 PM

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>So, as you can
see, I'm using the Eclipse platform in a way that most people would never
>dream of

Actually, I think you'd be surprised :-)

Okay, so you do control the application that your bundles are installing
into. Here's what I would do:

1) Define a bundle header called Bundle-ImmediateActivation (or whatever).
Add it to the bundles that you want to be started on installation
2) Write a bundle (lets call it X) that sits in your core application.
That bundle registers a BundleListener.
3) The BundleListener is interested in "Bundle Install" events
- when it sees one, it gets the Bundle object from the BundleEvent, scans
the headers of the Bundle for the ImmediateActivation header, and if present
calls Bundle.start().

This will work for your application, and also would work in my hypothetical
app that _doesn't_ want the bundle started immediately - I simply leave
out the X bundle.

Now, bundle X still has to be started by something, but you can add that
to config.ini (or start it from your main IPlatformRunnable). That's not
a problem because bundle X is not installed by Update Manager, it's part
of your core application.

How does that sound?

Regards
Neil


On 4/10/06, Simon J Archer <sarcher@xxxxxxxxxx>
wrote:

Hi Neil 

Please don't get me wrong, I really appreciate the dialog... Yes, I have
to admit that my scenario is a little new to the traditional Eclipse developer
that is always thinking about an IDE running on a desktop and a user sitting
there with a mouse.  My application has none of these... let me explain.

The application I am building is an embedded Java application that runs
on an embedded Linux box, on a shelf in a factory somewhere.  The
application is totally headless.  It has TCP/IP, plus a bunch of other
RFID hardware devices hanging off of it.  The application is designed
to be very self sufficient, checking for updates regularly, and performing
all the necessary care and feeding of itself to run unassisted.  As
for a user, the closest I think of is some guy in the warehouse driving
a fork-lift, but as you can imagine he has no idea about the application,
about Eclipse, or about the fact that my bundles need starting.  All
he cares about is shifting palettes through a dock-door and getting to
his next coffee break. 

So, as you can see, I'm using the Eclipse platform in a way that most people
would never dream of.  But I must stress that this requirement is
valuable to the IDE world too.  Whenever I building plug-ins for the
Eclipse IDE I still like to be able to practice good design where my model
plug-ins are quite separate from my UI plug-ins.  My model plug-ins
are purely model and have no dependency on the UI.  The UI plug-in
is an observer of the model and interacts with it in a very loosely coupled
manner.  Sure I could couple these guys, but it would inhibit reuse
and would make evolving the application significantly harder due to the
dependency upon an existing UI. 

Please don't stop responding, I really do appreciate it.  I shall
investigate the IPlatformRunnable interface some more.

Cheers 

Simon

"Neil Bartlett" <neil@xxxxxxxxxxxxxx>
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Simon,

There must be a bundle somewhere that is active - and therefore has a BundleContext
- otherwise your application is doing nothing...

Do you mean that you are installing via Update Manager a set of bundles,
and prior to the Update you don't have any of your own bundles already
installed in the target application? If you are installing into a completely
clean Eclipse application such as the SDK, then yes you have a problem
because you can't put your Bundle.start() code into any of the pre-existing
bundles. However it's difficult to see what possible use the pre-existing
bundles could be making of your service...

How about letting the end user decide whether to start the bundles? You
could popup a little dialog... and since that's already a UI thing there
would be no problem using IStartup (just keep the popup code in a separate
bundle). In non-UI applications you can do something else, like a single
line of code on the IPlatformRunnable...

If you have implemented an IPlatformRunnable and have declared it through
the org.eclipse.core.runtime.application extension point, then you can
get the Bundle and call start() on it there. However if you have the level
of configuration control to define and start an application, why don't
you have the ability to modify config.ini?

>All I want is to build a bundle
on the Eclipse platform that starts as soon as it is installed; >it's
really as simple as that.

Okay, but that's really none of the bundle's business. It's the responsibility
of the product assembler, or the administrator, or even the end user, to
decide when bundles start. Say for example I want to use your bundle, but
in my application I don't want it to start immediately. I'd be out of luck,
because your bundles think that they must always be running no matter what
application they are in.

Sorry if I still don't seem to be getting your problem. If it's still not
clear to me after your next reply I'll shut up and let somebody else have
a go!

Good luck
Neil

On 4/9/06, Simon J Archer <sarcher@xxxxxxxxxx
> wrote: 

Hi Neil 

Thanks for the response.  I am very familiar with all the tricks available
via the BundleContext, but until my bundle is started, and a BundleContext
provided to me, none are possible.  The point of my posting is exactly
this: My model-based bundle that registers a service is never started.
 I hope now that you understand my dilemma. 

Regarding IStartup, that is in a UI plugin, and sadly the extension point
requires the BundleActivator to implement an interface in a UI plugin.
 I do not want to create an unholy dependency upon any UI plugin,
since my bundle is purely headless.  Requiring the Eclipse UI would
be madness.  All I want is to build a bundle on the Eclipse platform
that starts as soon as it is installed; it's really as simple as that.

Your point regarding IPlatformRunnable
is of interest to me.  If my bundle is not yet started, how am I to
make use of IPlatformRunnable?  Remember, I'm asking for a solution
to the problem of providing one (or more) model-based bundles that simply
register OSGi services.  OSGi services are not widely used yet in
the Eclipse community, so I'm likey one of the few that is running into
this problem. 

Thanks 

Simon

"Neil Bartlett" <neil@xxxxxxxxxxxxxx >

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Subject	Re: [equinox-dev] Creating and Starting a BundleActivator when the        framework launches

Simon,

Maybe I misunderstood your problem, but there are a number of easy solutions
and I don't really see why you've dismissed all of them.

Firstly, why can't you get the Bundle object? You seem to be under the
impression that the Bundle object is only available within the bundle that
it describes. Actually any bundle can get the Bundle object for any other
bundle just by calling getBundle(id) or getBundles() on its own BundleContext.
You could even write a bundle that uses a BundleListener to listen for
Bundle Installed events, checks the value of some header you define eg
"Bundle-EarlyActivation", and immediately starts those bundles.

If that's no good, what's wrong with IStartup? That works in any Eclipse
application that uses the Workbench. Is your application entirely headless?

Finally, if your application is headless (or if it isn't), you can get
the Bundle and start it from the IPlatformRunnable.

Regards,
Neil



On 4/9/06, Simon J Archer <sarcher@xxxxxxxxxx
> wrote: 

So my choices are: 

- Call the Bundle object's start() method, or 
- Update a configuration file in the local filesystem.

Hmmm, neither of these seem to be what I'm looking for: Calling the Bundle's
start() method assumes that I can get the Bundle object for my bundle,
which I usually do through the BundleContext, which is not created until
the BundleActivator's start has been called.  The configuration file
is not really feasible since I'm talking about building a bundle that is
available for installation from an update site.  I would imagine that
updating the config.ini is something you need to do by hand before Eclipse
is started. 

Here's my scenario, in a nutshell: 

"I wish to write a bundle that can be installed into Eclipse from
a update site.  The bundle is "pure model" (no UI) and has
a BundleActivator that simply creates an instance of the model class and
registers it as a service with the OSGi framework.  To do this I shall
be using the traditional BundleContext APIs, and NOT declarative services.
 Other bundles will acquire the imported service from the OSGi framework
and therefore will never touch any of the bundle's classes directly.  Even
the service interface used to implement the service might be defined by
another bundle, for which import/export package dependencies will exist."

So far I'm stumped.  Surely this simple scenario should be supported
by the Eclipse platform.  Here are some possible ways that Eclipse
could be enhanced to help: 

1.  Add a manifest header that informs the platform that this bundle
should be started as soon as it is installed.  Even broadening the
legal values for Eclipse-LazyStart might suffice. 

2.  Add an extension point to the platform (not UI) that causes the
bundle to be started as soon as it is installed. 

3.  Enhance the platform so that when a bundle with a BundleActivator
and an Export-Service header is installed it is automatically started.
 This is probably my least favorite of the 3, since an Export-Service
header is purely informational and therefore optional.


I'm happy to file a feature request in bugzilla for this. Comments? Suggestions?

Thanks 

Simon

BJ Hargrave/Austin/IBM@IBMUS

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If you start the bundle with Bundle.start(), then the framework will 
persistently mark it started and will restart each time the framework is
started.

If you launch the framework with -console, you can follow that with 
"install some://bundle/url start" to install and start a bundle.

You can also mark it to be started in the configuration/config.ini file.
See the osgi.bundles key:

# The comma-separated list of bundles which are automatically installed
and optionally started
# once the system is up and running.  Each entry if of the form
#     <URL | simple bundle location>[@ [<startlevel>]
[":start"]]
# If the startlevel is omitted then the framework will use the default
start level for the bundle.
# If the "start" tag is added then the bundle will be marked
as started 
after being installed.
# Simple bundle locations are interepreted as relative to the framework's
parent directory.
# The startlevel indicates the OSGi start level at which the bundle should
run.
# If this value is not set, the system computes an appropriate default.
osgi.bundles=org.eclipse.equinox.common@2:start, 
org.eclipse.update.configurator@3:start, org.eclipse.core.runtime@start

BJ Hargrave
Senior Technical Staff Member, IBM
OSGi Fellow and CTO of the OSGi Alliance
hargrave@xxxxxxxxxx
Office: +1 407 849 9117 Mobile: +1 386 848 3788



Simon J Archer/Raleigh/IBM@IBMUS 
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2006-04-08 07:24 AM
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Subject
[equinox-dev] Creating and Starting a BundleActivator when the  framework
launches







It is my understanding that simply having a BundleActivator class and a
Bundle-Activator header in the MANIFEST.MF is not enough to force the 
bundle's activator to be created and started by Equinox when the framework
is launched. 

I have learned that adding Eclipse-LazyStart: true to the MANIFEST.MF is
the way ensure that the bundle's activator is started when one of its 
classes is first touched by another bundle. 

But how am I to create a bundle that has a BundleActivator that is created
and started when the OSGi framework is launched?  I am aware of the
org.eclipse.ui.startup extension point and accompanying IStartup class,
but I do not want to use that when my bundle is "pure model",
since they 
reside in an Eclipse UI plug-in.  I don't want to couple my model
to 
anything UI related. 

I'm building plugins that will run in the Eclipse IDE rather than pure
OSGi bundles, so I'm using an "Eclipse Application" launch configuration.
It is curious that only the "Equinox OSGi Framework" launch configurations
allow you to specify the default start level for a bundle and whether it
will start automatically when the framework launches. 

While I understand that the early creation and starting of a bundle 
activator is considered a bad thing by many Eclipse developers, it should
still be possible and should not be this hard. 

Thanks 

Simon 
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-- 
Neil Bartlett
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Fax: +44 (0) 20 7043 8329

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-- 
Neil Bartlett
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Fax: +44 (0) 20 7043 8329 

LinkedIn Profile: https://www.linkedin.com/in/neilbartlett
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