Merge branch 'fix_mpi_gather_scatter' into 'master'

Fix mpi gather scatter

See merge request core/dune-common!885

dune/common/parallel/mpicommunication.hh

@@ -307,12 +307,12 @@ namespace Dune
 
     //! @copydoc Communication::igather
     template<class TIN, class TOUT = std::vector<TIN>>
-    MPIFuture<TOUT, TIN> igather(TIN&& data_in, TOUT&& data_out, int root){
+    MPIFuture<TOUT, TIN> igather(TIN&& data_in, TOUT&& data_out, int root) const{
       MPIFuture<TOUT, TIN> future(std::forward<TOUT>(data_out), std::forward<TIN>(data_in));
       auto mpidata_in = future.get_send_mpidata();
       auto mpidata_out = future.get_mpidata();
       assert(root != me || mpidata_in.size()*procs <= mpidata_out.size());
-      int outlen = me==root * mpidata_in.size();
+      int outlen = (me==root) * mpidata_in.size();
       MPI_Igather(mpidata_in.ptr(), mpidata_in.size(), mpidata_in.type(),
                   mpidata_out.ptr(), outlen, mpidata_out.type(),
                   root, communicator, &future.req_);
@@ -345,7 +345,7 @@ namespace Dune
       MPIFuture<TOUT, TIN> future(std::forward<TOUT>(data_out), std::forward<TIN>(data_in));
       auto mpidata_in = future.get_send_mpidata();
       auto mpidata_out = future.get_mpidata();
-      int inlen = me==root * mpidata_in.size();
+      int inlen = (me==root) * mpidata_in.size()/procs;
       MPI_Iscatter(mpidata_in.ptr(), inlen, mpidata_in.type(),
                   mpidata_out.ptr(), mpidata_out.size(), mpidata_out.type(),
                   root, communicator, &future.req_);

dune/common/parallel/test/CMakeLists.txt

@@ -51,3 +51,10 @@ dune_add_test(SOURCES mpipacktest.cc
               TIMEOUT 300
               CMAKE_GUARD MPI_FOUND
               LABELS quick)
+
+dune_add_test(SOURCES mpigatherscattertest.cc
+              LINK_LIBRARIES dunecommon
+              MPI_RANKS 2
+              TIMEOUT 300
+              CMAKE_GUARD MPI_FOUND
+              LABELS quick)

dune/common/parallel/test/mpigatherscattertest.cc

+// -*- tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 2 -*-
+// vi: set et ts=4 sw=2 sts=2:
+
+#include <config.h>
+
+#include <iostream>
+#include <array>
+#include <vector>
+
+
+#include <dune/common/parallel/mpihelper.hh>
+#include <dune/common/parallel/mpicommunication.hh>
+#include <dune/common/exceptions.hh>
+
+using namespace Dune;
+
+int main(int argc, char** argv){
+  MPIHelper & mpihelper = MPIHelper::instance(argc, argv);
+  auto cc = mpihelper.getCommunication();
+  int rank = cc.rank();
+  int size = cc.size();
+
+  std::array<double, 2> data = {1.0 + rank, 2.0 + rank};
+
+  auto gathered = cc.igather(data, std::vector<double>(rank==0?2*size:0), 0).get();
+
+  for(auto& d : gathered)
+    d += 1;
+
+  cc.iscatter(gathered, data, 0).get();
+  if(data[0] != 2+rank ||
+     data[1] != 3+rank){
+    DUNE_THROW(Exception, "Wrong result after gather - scatter");
+  }
+
+  return 0;
+}