Address the pesky 'MPI_Comm as void*' problem with the SUNDIALS interfaces #15113
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The correct comment is here: #15086 (review) |
| Assert(v->content != nullptr, ExcInternalError()); | ||
| auto *pContent = | ||
| reinterpret_cast<NVectorContent<VectorType> *>(v->content); | ||
| return pContent->get_mpi_communicator(); | ||
| } |
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Why did
template <typename VectorType,
std::enable_if_t<is_serial_vector<VectorType>::value, int>>
void *get_communicator_as_void_ptr(N_Vector)
{
// required by SUNDIALS: MPI-unaware vectors should return the nullptr
// as comm
return nullptr;
}disappear? Is &MPI_COMM_SELF==nullptr?
edit: Clarified "this".
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There were two specializations of the function, one for serial and one for parallel vectors (enabled or disabled via std::enable_if) because the former do not have a get_communicator() member function.
I've outsourced that decision to the get_mpi_communicator() free function above now that returns MPI_COMM_SELF for serial vectors. Are you saying that we should just return nullptr if a vector is serial, regardless of whether we configured for MPI or not?
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Maybe something like this in the current place?
diff --git a/include/deal.II/sundials/n_vector.templates.h b/include/deal.II/sundials/n_vector.templates.h
index e5e9db4bd2..e4a42d659a 100644
--- a/include/deal.II/sundials/n_vector.templates.h
+++ b/include/deal.II/sundials/n_vector.templates.h
@@ -619,8 +619,12 @@ namespace SUNDIALS
(void)v;
return nullptr;
# else
- // We need to cast away const here, as SUNDIALS demands a pure `void *`.
- return &(const_cast<MPI_Comm &>(get_communicator<VectorType>(v)));
+ if (is_serial_vector<VectorType>::value == false)
+ // We need to cast away const here, as SUNDIALS demands a pure `void
+ // *`.
+ return &(const_cast<MPI_Comm &>(get_communicator<VectorType>(v)));
+ else
+ return nullptr;
# endif
}
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I convinced myself that that is the right way to go and pushed an updated commit.
We can't ask a default-created vector for its MPI communicator if we only later initialize it.
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This required a bit more work, but it works now at least locally. |
This patch block #15086, and so I would ask for expedited review.
See #15086 (review) Fundamentally, this patch works around the issue mentioned here: LLNL/sundials#275
@sebproell @stefanozampini FYI.