Re: Reference Tracking and Leases.

On Wed, Dec 05, 2007 at 02:16:54PM -0600, Gregg Wonderly wrote:
> Peter Jones wrote:
>> FYI, this seems very similar to how the client side of DGC works under
>> the covers.  For DGC, instead of a smart proxy, the tracked object is
>> a so-called "live remote reference" object inside a remote proxy--
>> BasicObjectEndpoint for JERI (or sun.rmi.transport.LiveRef for JRMP);
>> the analogue of the Lease is the object ID and transport-layer
>> endpoint (which are contained in the live reference) and a specialized
>> lease renewal/cancellation protocol.  For JERI, the implementation is
>> in com.sun.jini.jeri.internal.runtime.AbstractDgcClient (and the spec
>> is in BasicObjectEndpoint).
>
> Right, that's what I've seen.  The work that I did was to just
> expose that leasing at the application level so that I can take
> specific actions at the point that such action is necessary.  For
> example, I have a smart proxy who's server side endpoint streams
> data over a UDP socket, as well as making normal RMI centric calls.
> Those RMI calls would get a RemoteException when the DGC discovered
> that the client was gone.  But the UDP pump would not see any
> particular failures.  So, having the lease in place to manage that
> issue helps to alert the servers UDP generation that there is no
> longer a path so that it can throw a RemoteException which will
> allow the server to stop pumping out UDP events.

I may not be understanding this scenario fully, but wouldn't
implementing the (DGC-based) java.rmi.server.Unreferenced callback on
the per-client exported remote objets have helped with this?

Regardless, though, there are reasons to do this explicitly at a
higher level, like how the way that the implicit DGC model ported
more-or-less directly from RMI/JRMP doesn't work with certain JERI
features, like applying constraints or Subject-based credentials to
the DGC lease communication.

-- Peter

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