From: Wolfgang Bangerth Date: Thu, 8 Mar 2018 14:54:25 +0000 (-0700) Subject: Better document one place. X-Git-Tag: v9.0.0-rc1~353^2 X-Git-Url: https://gitweb.dealii.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=refs%2Fpull%2F6009%2Fhead;p=dealii.git Better document one place. --- diff --git a/source/dofs/dof_handler_policy.cc b/source/dofs/dof_handler_policy.cc index 8b20aa899b..deb86f6861 100644 --- a/source/dofs/dof_handler_policy.cc +++ b/source/dofs/dof_handler_policy.cc @@ -4114,8 +4114,19 @@ namespace internal triangulation->coarse_cell_to_p4est_tree_permutation, triangulation->p4est_tree_to_coarse_cell_permutation); - // This barrier is crucial so that messages between phases - // 1&2 don't mix. + // have a barrier so that sends from above and below this + // place are not mixed up. + // + // this is necessary because above we just see if there are + // messages and then receive them, without discriminating + // where they come from and whether they were sent in phase + // 1 or 2 in communicate_mg_ghost_cells() on another + // processor. the need for a global communication step like + // this barrier could be avoided by receiving messages + // specifically from those processors from which we expect + // messages, and by using different tags for phase 1 and 2, + // but the cost of a barrier is negligible compared to + // everything else we do here const int ierr = MPI_Barrier(triangulation->get_communicator()); AssertThrowMPI(ierr);