Marco Bungart <m.bung...@gmx.net> wrote on 12/01/2014 06:48:47 AM:
>
> i am playing around with the Elastic-feature added in X10 2.5.0. Are
> PlaceLocalHandles supported with Elastic? If so, where is the
> entry-point of the new place(s)? The code appended throws a
> NullPointerException, when a place is added.
> Line 60 to 76 enables Elasticity on the program, but seems overkill for
> me. Is there a shorter / more elegant solution for this?
Hi,
I would say we haven't done a good job of supporting them (yet). It's
a specific instance of a design problem we're still thinking through about
the role of Place-specific data in Elastic computations.
In some of the programs we've been writing, we find ourselves storing
all of the "interesting" data in resilient maps
(x10.util.resilient.ResilientMap), so PlaceLocalHandle becomes less
important.
We've also played around with implementing a
ResilientPlaceLocalHandle on top of a ResilientMap to keep a familiar
interface, but it seems a bit forced at times.
Another view is to de-emphasize Places as the "home" location of data
and instead think about data being kept in resilient, elastic in-memory
stores (that are co-located with X10 Places), and the primary method of
computation is to go to whatever Places are the current primary location
for the key/value pairs of interest and compute in them. So, the Grid
becomes the primary data abstraction and the Place is less central than in
classic X10.
I guess that's a long way of saying that what you did is currently
necessary in Elastic X10 if you want to use a PlaceLocalHandle. But, we're
not entirely sure that is the style we want to promote, so we haven't made
the natural extensions needed to PlaceLocalHandle to make it less painful.
(For example, providing a way to register/deregister PlaceLocalHanlde
initialization closures with the X10 runtime so that when a new Place is
added to a computation, we can ensure that a set of PlaceLocalHandles have
all been initialized before any activities are scheduled to execute on the
Place).
Glad to hear you are experimenting with Elastic X10. We will be
making a 2.5.1 release by the end of this week that includes more
improvements for Resilient/Elastic X10. Would be interested to hear your
feedback...
--dave
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