[Trilinos-Users] Best practice to modify elements of a Tpetra::Vector with openmp?

[Hoemmen, Mark]

Please refer to the following, commented example:

Trilinos/packages/tpetra/core/example/Lesson02-Map-Vector/lesson02_read_modify_vec_kokkos.cpp

mfh



On 6/6/17, 3:11 PM, "Trilinos-Users on behalf of trilinos-users-request at trilinos.org" <trilinos-users-bounces at trilinos.org on behalf of trilinos-users-request at trilinos.org> wrote:

>Date: Fri, 12 May 2017 17:36:42 -0400
>From: Wen Yan <wenyan4work at gmail.com>
>To: "trilinos-users at trilinos.org" <trilinos-users at trilinos.org>
>Subject: [Trilinos-Users] Best practice to modify elements of a
>	Tpetra::Vector with openmp?
>Message-ID: <D1AADFE6-3AB8-4259-8C00-040F2BE02EDF at gmail.com>
>Content-Type: text/plain; charset=us-ascii
>
>Hi Trilinos,
>
>I was wondering what is the best practice to modify the elements of a Tpetra::Vector or a Tpetra::MultiVector. The document mentioned that ArrayRCP<T> is not thread safe, and suggested using Kokkos::View, but not much details are discussed. I am using Kokkos::OpenMP as the execution backend of Tpetra.
>
>Assume xRcp is Teuchos::Rcp<Tpetra::MultiVector>
>
>To use Kokkos::View, I can do this, but it is awkward and the Kokkos documentation does not include much useful information about these:
>
>//   auto x_2d = xRcp->getLocalView<Kokkos::HostSpace>();
>//   auto x_1d = Kokkos::subview(x_2d, Kokkos::ALL(), 0);
>//   xRcp->modify<Kokkos::HostSpace>();
>//   const size_t localLength = vecRcp->getLocalLength();
>//   #pragma omp parallel for
>//   for (size_t k = 0; k < localLength; ++k) {
>//        x_1d[k]=k;
>//   }
>
>
>The ArrayRCP interface is more straightforward, but it is mentioned in the document that its reference counting is not compatible with multi threading. I was wondering if it is unsafe to write a simple for loop like this to modify the content of a Tpetra::Vector
>
>// auto xArrayRcp = xRcp->getDataNonConst();
>// const int localLength = xRcp->getLocalLength();
>// #pragma omg parallel for
>// for (int i = 0; i < localLength; i++) {
>//     xArrayRcp[i]=I; 
>// }
>
>
>Thanks a lot!
>Wen Yan
>
>