dolfin team mailing list archive

["Martin Sandve Alnæs" <martinal@xxxxxxxxx>]

2008/11/1 Garth N. Wells <gnw20@xxxxxxxxx>:
> Martin Sandve Alnæs wrote:
>>
>> Are there any plans for multicore support in DOLFIN, that is
>> automatic utilization of multiple CPU cores without significant
>> user intervention, in the near future? (For example using OpenMP).
>>
>
> No immediate plans (message passing is the immediate priority), but
> obviously this would be very nice to have and we don't want our design to
> preclude it.

Ok.

>> If yes, am I the only one who thinks it would be a good idea
>> to consider this in the new Function design?
>>
>
> You may be the only that knows enough about multi-threaded programming to be
> in a position to think properly about it.

Ok, but I don't really know that much about it.

>> I just want to point this out since I think this issue has been too
>> downplayed in the design discussions. And I don't think anyone
>> wants yet another redesign of Function within the next months...
>>
>> The main issue is that iterating over cells in a mesh and calling a
>> Function currently involves side effects, modifying its mutable members
>> cell and facet. Thus the user would have to construct multiple Function
>> objects for a Function to be used in basically any multicore situation.
>> Any solution to this must involve sending all kinds of cell data needed
>> as arguments to eval. Exactly how this should look is a design discussion.
>>
>
> So if we remove
>
>  mutable Cell* _cell
>  mutable int _facet
>
> from the private member data of Function, does this resolve the biggest
> design issue for running multi-threaded?

Yes. Otherwise the threads will overwrite each others current cell all the time.

User functions need to be threadsafe too though, but we can't do
anything about that.

--
Martin