Do not rely on managed memory in EM PIC tutorial (#164)

Author: atmyers

ExampleCodes/Particles/ElectromagneticPIC/Source/EMParticleContainerInit.cpp

@@ -70,10 +70,10 @@ InitParticles(const IntVect& a_num_particles_per_cell,
         const auto lo = amrex::lbound(tile_box);
         const auto hi = amrex::ubound(tile_box);
 
-        Gpu::ManagedVector<unsigned int> counts(tile_box.numPts(), 0);
+        Gpu::DeviceVector<unsigned int> counts(tile_box.numPts(), 0);
         unsigned int* pcount = counts.dataPtr();
 
-        Gpu::ManagedVector<unsigned int> offsets(tile_box.numPts());
+        Gpu::DeviceVector<unsigned int> offsets(tile_box.numPts());
         unsigned int* poffset = offsets.dataPtr();
 
         amrex::ParallelFor(tile_box,
@@ -109,7 +109,16 @@ InitParticles(const IntVect& a_num_particles_per_cell,
 
         Gpu::exclusive_scan(counts.begin(), counts.end(), offsets.begin());
 
-        int num_to_add = offsets[tile_box.numPts()-1] + counts[tile_box.numPts()-1];
+        unsigned int last_offset;
+        unsigned int last_count;
+#ifdef AMREX_USE_GPU
+        Gpu::dtoh_memcpy(&last_offset,offsets.dataPtr()+tile_box.numPts()-1,sizeof(unsigned int));
+        Gpu::dtoh_memcpy(&last_count,counts.dataPtr()+tile_box.numPts()-1,sizeof(unsigned int));
+#else
+        std::memcpy(&last_offset,offsets.dataPtr()+tile_box.numPts()-1,sizeof(unsigned int)
+        std::memcpy(&last_count,counts.dataPtr()+tile_box.numPts()-1,sizeof(unsigned int)
+#endif
+        int num_to_add = last_offset + last_count;
 
         auto& particles = GetParticles(lev);
         auto& particle_tile = particles[std::make_pair(mfi.index(), mfi.LocalTileIndex())];