Dear list,
i am writing since i am an OpenMP user, but i am actually quite
curious in understanding the future directions of c++.
my parallel usage is actually relatively trivial, and is covered by OpenMP
2.5 (openmp 3.1 with supports for iterators would be better but is not
available in msvc)
99% of my user needs are about parallel loops, and with c++11 lambdas i
could do a lot.
However i am really not clear on how i should equivalently handle "private"
and "firstprivate of OpenMP, which allow to create objects that persist in
the threadprivate memory during the whole lenght of a for loop. I now use
OpenMP 2.5 and i have a code that looks like the following
https://kratos.cimne.upc.es/projects/kratos/repository/entry/kratos/kratos/solving_strategies/builder_and_solvers/residualbased_block_builder_and_solver.h
which does an openmp parallel Finite Element assembly.
The code i am thinking of is somethign like:
//here some to-be-threadprivate matrices are allocated. This
allocation is very SLOW so i don't want to do it often
LocalSystemMatrixType LHS_Contribution = LocalSystemMatrixType(0,
0);
LocalSystemVectorType RHS_Contribution = LocalSystemVectorType(0);
Element::EquationIdVectorType EquationId;
#pragma omp parallel for firstprivate(nelements, LHS_Contribution,
RHS_Contribution, EquationId )
for (int k = 0; k < nelements; k++)
{
ModelPart::ElementsContainerType::iterator it = el_begin + k;
//iterator is random access so we do this trick to have a one line in
openmp 2.5
//calculate elemental contribution ---> HERE I USE
LHS_Contribution etc as scratch space, so i don't have to reallocate it
pScheme->CalculateSystemContributions(*(it.base()),
LHS_Contribution, RHS_Contribution, EquationId, CurrentProcessInfo);
//assemble the elemental contribution --> HERE I USE LOCKS
to sum contributions to the sparse matrix A (it appeared to work faster
than using atomics)
Assemble(A, b, LHS_Contribution, RHS_Contribution,
EquationId, mlock_array);
}
}
the big question is ... how shall i handle the threadprivate scratchspace
in HPX?? Lambdas do not allow to do this ...
that is, what is the equivalente of private & of firstprivate??
thanks you in advance for any clarification or pointer to examples
regards
Riccardo
--
*Riccardo Rossi*
PhD, Civil Engineer
member of the Kratos Team: www.cimne.com/kratos
Tenure Track Lecturer at Universitat Politècnica de Catalunya,
BarcelonaTech (UPC)
Full Research Professor at International Center for Numerical Methods in
Engineering (CIMNE)
C/ Gran Capità, s/n, Campus Nord UPC, Ed. C1, Despatx C9
08034 – Barcelona – Spain – www.cimne.com -
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