Module system notification mechanism

[Bryan Atsatt]

It seems simple enough to put the module in a failed state if a
module-init event handler throws an exception. Is this not sufficient?

The lazy init feature sounds like a nice optimization, but doesn't
strike me as a must-have. Have you seen use-cases that require it? Are
they init order issues?


(I am sensitive to your meta point here, but... If 277 is going to
exist, there are some rather obvious, desirable features which it will
need, just as OSGi needed them. I _don't_ like the fact that we are
re-inventing rather than re-using OSGi, but that is how it has played
out, despite all protestations. As long as we can still attain the goal
of meaningful interoperation, it seems irresponsible to leave out
features like this. And yes, we must nail down the interoperation model
before we go much/any farther.)

Glyn Normington wrote:
>
> Yes, but my point was that separating lifecycle out in that way would
> make it harder to enforce constraints like "if a module's state is
> initialised, the module's activator completed successfully".
>
> JSR 291 solved this problem with additional module states and error
> handling. It also supports lazy module initialisation triggered by the
> first class load from a module. How much of this should JSR 277 re-invent?
>
> Glyn
>
> *Bryan Atsatt <bryan.atsatt at ORACLE.COM>* wrote on 22/06/2007 06:12:48 PM:
>
>  > I think that is part of Stanley's point here: the module system isn't
>  > responsible, as it merely generates the events. Some *other* system
>  > could then take on lifecycle based on these events.
>  >
>  > Glyn Normington wrote:
>  > >
>  > > Hmmm. I thought so too (apart from reinventing the OSGi lifecycle
> event,
>  > > of course), but I wonder if the module system needs to be directly
>  > > responsible for driving an activator in case it fails to terminate (in
>  > > which case the module needs to enter some kind of error or inactive
> state)?
>  > >
>  > > Glyn
>  > >
>  > > *"Richard S. Hall" <heavy at UNGOVERNED.ORG>* wrote on 22/06/2007
> 01:21:48 PM:
>  > >
>  > >  > I think your suggestion is reasonable.
>  > >  >
>  > >  > -> richard
>  > >  >
>  > >  > Stanley M. Ho wrote:
>  > >  > > Hi JSR 277 experts,
>  > >  > >
>  > >  > > Since we have been discussing some issues around the module
> instances'
>  > >  > > lifetime lately, I think it's probably a good time to bring up a
>  > > related
>  > >  > > topic for discussion.
>  > >  > >
>  > >  > > As I reviewed the feedbacks from the EDR comments, from our
> previous
>  > >  > > discussions, as well as from my discussions with the teams in SE
>  > > and EE,
>  > >  > > there were a few suggestions related to the module
> instances'lifetime:
>  > >  > >
>  > >  > > 1. The module system shall provide a way to monitor various
> events,
>  > > e.g.
>  > >  > > module initialized, module released, etc.
>  > >  > > 2. The module system shall allow a module to have activator
> code. The
>  > >  > > activator code would be executed right before the module is fully
>  > >  > > initialized and when the instance is released.
>  > >  > > 3. A module shall have a way to be stopped.
>  > >  > >
>  > >  > > Having these suggestions don't mean we have to do all of them,
> and I
>  > >  > > would like to get your inputs.
>  > >  > >
>  > >  > >
>  > >  > > From my perspective, having a way to monitor module system's
> events
>  > >  > > (i.e. #1) seems very reasonable and useful, especially the use
>  > > cases are
>  > >  > > very common. In fact, many teams in SE have expressed the needs in
>  > >  > > monitoring the module system's events in their class libraries
> in some
>  > >  > > degrees, so these libraries would react and behave
> appropriately. There
>  > >  > > are also other class libraries sitting on top of the JRE that have
>  > >  > > similar needs.
>  > >  > >
>  > >  > > For #2, this is a use case I gathered from EE, and this would
> be used
>  > >  > > mainly for registering and unregistering services when a
> module has
>  > > been
>  > >  > > initialized or is released. Not that I think this is
> unimportant, but I
>  > >  > > am not yet convinced this is something we need to support
> directly at
>  > >  > > the module system level. For instance, if the module system
>  > > notification
>  > >  > > mechanism (i.e. #1) is available, it should be possible for the EE
>  > >  > > server (or other apps that require similar functionality) to
> build a
>  > >  > > simple activator layer on top of the module system.
>  > >  > >
>  > >  > > For #3, the use case is that some EE servers might want to
> have the
>  > >  > > ability to "stop" a module by disabling the module's
> classloader when
>  > >  > > the module instance is released. In general, disabling a
> classloader is
>  > >  > > an uncommon and dangerous operation to perform, and it also
>  > > violates the
>  > >  > > current classloading spec. While I agreed we should make this
> use case
>  > >  > > possible, I don't think this is something we want to push into the
>  > >  > > module system.; I believe there are alternatives we could
> consider to
>  > >  > > achieve the same result. For example, suppose there are APIs
> available
>  > >  > > to disable a classloader (might come from the classloading
> project) and
>  > >  > > the module system notification mechanism (i.e. #1) is
> available, it
>  > >  > > should be possible for the EE servers to hook into the
> notification
>  > >  > > mechanism, and disable the specific classloader it wants when
> a module
>  > >  > > instance is released from the module system.
>  > >  > >
>  > >  > >
>  > >  > > To keep things simple, I suggest we should support #1, and I
> hope this
>  > >  > > should be sufficient to enable other applications (e.g. EE
> servers) to
>  > >  > > support #2 and #3. I would like to hear what your thoughts are.
>  > >  > >
>  > >  > > - Stanley
>  > >
>  > >
>  > >
>  > >
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