From: Wolfgang Bangerth Date: Sun, 13 Aug 2017 21:50:03 +0000 (-0600) Subject: Better document what the ghost DoF index exchange does. X-Git-Tag: v9.0.0-rc1~1269^2 X-Git-Url: https://gitweb.dealii.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=refs%2Fpull%2F4822%2Fhead;p=dealii.git Better document what the ghost DoF index exchange does. While there, also tighten up the logic of what user flags we set, clear, and when. --- diff --git a/source/dofs/dof_handler_policy.cc b/source/dofs/dof_handler_policy.cc index 615b138469..5e3ac54c98 100644 --- a/source/dofs/dof_handler_policy.cc +++ b/source/dofs/dof_handler_policy.cc @@ -3208,6 +3208,11 @@ namespace internal for (unsigned int i=0; iset_user_flag(); - else + // if we are in phase 1, then all ghost cells had their user + // flag set, indicating that they need to receive data from + // the cell's owner. if the data we received in phase 1 was + // complete, then we need not receive data from there again. + // consequently, remove the user flag from this ghost cell. + // + // if the data we received was *not* complete (because the + // owning processor of that cell had not gotten information + // from even more remote processors yet), then we leave + // the user flag set + // + // in any case, if we are treating this cell right now, + // then its user flag must have been set, and we can + // assert that that is so. + Assert (dealii_cell->user_flag_set(), ExcInternalError()); + if (complete) dealii_cell->clear_user_flag(); const_cast(dealii_cell)->set_dof_indices(dof_indices); @@ -3242,6 +3260,24 @@ namespace internal + /** + * A function that communicates the DoF indices from that subset of + * locally owned cells that have their user indices set to the + * corresponding ghost cells on other processors. + * + * This function makes use of the user flags in the following + * way: + * - On locally owned cells, the flag indicates whether we still + * need to send the DoF indices to other processors on which + * the current cell is a ghost. In phase 1, this is true for + * all locally owned cells that are adjacent to ghost cells + * in some way. In phase 2, this is only true if before phase + * 1 we did not know all dof indices yet + * - On ghost cells, the flag indicates whether we still expect + * information to be sent to us. In phase 1, this is true for + * all ghost cells. In phase 2, this is only true if we + * did not receive a complete set of DoF indices in phase 1. + */ template void communicate_dof_indices_on_marked_cells @@ -3289,7 +3325,12 @@ namespace internal Assert (triangulation != nullptr, ExcInternalError()); // first, collect cells and their dof_indices to send to - // interested neighbors + // interested neighbors. the functions called in the + // following loop only work on cells that are locally owned + // and are adjacent to ghost cells and that are marked via + // the user flag. in the first phase, all locally owned + // cells fall in this category, but we remove some of + // these flags later in this function typedef std::map> cellmap_t; @@ -3357,14 +3398,24 @@ namespace internal } else { + // this is a locally owned cell. + // + // if we are in phase 1: if it is + // complete already, then we have sent its information + // to the other processors that need it above, and we don't + // need to do so again in phase 2. if it wasn't + // complete, then it will be completed below, and we + // will have to send the completed information a + // second time. + // + // if we are in phase 2, nothing we do matters, so + // we just run this loop anyway local_dof_indices.resize (cell->get_fe().dofs_per_cell); cell->get_dof_indices (local_dof_indices); - if (local_dof_indices.end() != + if (local_dof_indices.end() == std::find (local_dof_indices.begin(), local_dof_indices.end(), numbers::invalid_dof_index)) - cell->set_user_flag(); - else cell->clear_user_flag(); } } @@ -3638,17 +3689,30 @@ namespace internal triangulation->save_user_flags(user_flags); triangulation->clear_user_flags (); - // mark all own cells for transfer - for (auto cell : dof_handler->active_cell_iterators()) - if (!cell->is_artificial()) - cell->set_user_flag(); - // figure out which cells are ghost cells on which we have // to exchange DoF indices const std::map > vertices_with_ghost_neighbors = triangulation->compute_vertices_with_ghost_neighbors (); + // mark all cells that either have to send data (locally + // owned cells that are adjacent to ghost neighbors in some + // way) or receive data (all ghost cells) via the user flags + for (auto cell : dof_handler->active_cell_iterators()) + if (cell->is_locally_owned()) + { + for (unsigned int v=0; v::vertices_per_cell; ++v) + if (vertices_with_ghost_neighbors.find (cell->vertex_index(v)) + != vertices_with_ghost_neighbors.end()) + { + cell->set_user_flag(); + break; + } + } + else if (cell->is_ghost()) + cell->set_user_flag(); + + // Send and receive cells. After this, only the local cells // are marked, that received new data. This has to be