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Re: [equinox-dev] When is DS done loading services?

Danail Nachev wrote:
Danail Nachev
Senior Software Engineer/Development Tools
ProSyst Labs EOOD
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stay in touch with your product.
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Richard S. Hall wrote:
Danail Nachev wrote:
Richard S. Hall wrote:
I don't think that what I said makes any assumptions about knowing the
exact dependencies. I think my point agrees with what you are saying,
which is that you have to wait for all plugins to start up (including
waiting for their dependencies on each other to be resolved) before you
can plug them into this core component that is going to use them.
Now I see your point (I think:) You are correct, but even without
dynamism, you need some guarantee that if bundle is started, it is
initialized (if all dependencies are available upfront). With
asynchronous DS you don't have this.
If not all dependencies are available, the unsatisfied components will
be registered synchronously with their required services becoming
available (which will happen in some other bundle's start() method in
most cases). The overall result is that after all bundles are started,
all services (which doesn't depend on external factors) are registered.
I think the difficult in this situation, if I understand correctly, is
that the core component does not know in advance which plugins will be
injected, so it doesn't know when it is ready to go. If it takes its
snapshot too early, it might miss some of them. I agree that this is an
issue, but I am not sure what the solution is. One possibility, using an
extender model-like approach, is to have the core component probe
installed plugin bundles to determine which plugins are available to
that it know which ones it has to wait for before continuing.

Doesn't this mean to duplicate DS work or duplicate information (if you
store the information twice (once for you and once for DS))?

Well, it isn't duplicating the work of DS, because DS doesn't do this, but it may duplicate some information.


The framework STARTED event has nothing to do with the readiness of the
application running on top of the framework, it has to do with the state
of the framework. The application must determine when it is ready. How
would the framework ever know if the application is "ready"?
You are right. But the DS asynchronous can make it hard to know when the
application is ready, if the application don't know what it is waiting
for. framework STARTED event seems to be the only valid event, which can
be used.
Well, this misappropriates the STARTED event, since you are trying to
construe it to be used for an application-level event.

When the application is the only one inside the framework, framework
STARTED event is, in fact, application-level event because the
application and framework are roughly the same thing - the framework is
the supporting infrastructure of the application. In the other cases I
agree with you (if there is more than one application), but then in the
other cases will don't have the problem with how long to wait for our
dependencies, because the applications are not short-lived and should
deal with the dynamism of OSGi.

You are free to think this, but in my view it is incorrect. The STARTED event only indicates that the framework has finished performing its startup tasks, nothing more and nothing less.


-> richard

-> richard

-> richard

Danail Nachev
Senior Software Engineer/Development Tools
ProSyst Labs EOOD
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stay in touch with your product.
-------------------------------------------------

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