JuliaParallel
Intended way to generate MPI.jl compatible C bindings
I am currently trying to generate MPI.jl compatible bindings of the C library HYPRE with the help Clang.jl . The current generator (found here https://github.com/termi-official/HYPRE.jl/blob/master/gen/generator.jl) creates files that have incompatible data types (see e.g. https://github.com/termi-official/HYPRE.jl/blob/master/lib/LibHYPRE.jl#L6), so I was wondering what the intended way to grab the correct MPI headers and data type definitions is?
cc @fredrikekre @Gnimuc
Can gen/src/MPIgenerator.jl be of inspiration? That script is used to generate the new low-level API.
(Slightly tangential, I am curious why there is a mismatch between https://github.com/JuliaParallel/MPI.jl/blob/3f21294863a55fbbefa8376bd489bceec84dc478/src/api/mpich.jl#L35 and https://github.com/fredrikekre/HYPRE.jl/blob/50c06161e9b654c5095dffd6a6b6e0978f1ae851/lib/LibHYPRE.jl#L6 since they are both (apparently) generated based on MPICH headers)
Thanks for the quick answer and your suggestion. I already tried to use this one as a template.
diff --git a/gen/generator.jl b/gen/generator.jl
index d6880cb..3df8f19 100644
--- a/gen/generator.jl
+++ b/gen/generator.jl
@@ -1,10 +1,18 @@
using Clang.Generators
-using HYPRE_jll, MPICH_jll
+using HYPRE_jll, MPIPreferences
cd(@__DIR__)
+if MPIPreferences.binary == "MPICH_jll"
+ import MPICH_jll: artifact_dir
+elseif MPIPreferences.binary == "OpenMPI_jll"
+ import OpenMPI_jll: artifact_dir
+else
+ error("Unknown MPI binary: $(MPIPreferences.binary)")
+end
+
hypre_include_dir = normpath(HYPRE_jll.artifact_dir, "include")
-mpi_include_dir = normpath(MPICH_jll.artifact_dir, "include")
+mpi_include_dir = normpath(artifact_dir, "include")
options = load_options(joinpath(@__DIR__, "generator.toml"))
but the types are still not matching - and we generate quite a bit of redundant code which is readily available in MPI.jl.
(Slightly tangential, I am curious why there is a mismatch between https://github.com/JuliaParallel/MPI.jl/blob/3f21294863a55fbbefa8376bd489bceec84dc478/src/api/mpich.jl#L35 and https://github.com/fredrikekre/HYPRE.jl/blob/50c06161e9b654c5095dffd6a6b6e0978f1ae851/lib/LibHYPRE.jl#L6 since they are both (apparently) generated based on MPICH headers)
I'm not entirely sure that file was automatically generated from header files,
This could maybe be of inspiration https://github.com/cesmix-mit/LAMMPS.jl/tree/main/res
I'm not entirely sure that file was automatically generated from header files,
It wasn't, that was manually translated.
I don't think it matters which one we use. I'm not sure why I changed them to unsigned? Perhaps changing them back to Cint would make things easier.
This could maybe be of inspiration https://github.com/cesmix-mit/LAMMPS.jl/tree/main/res
Sorry to ask again, but how exactly is the variable mpi_header_dir (https://github.com/cesmix-mit/LAMMPS.jl/blob/main/res/wrap.jl#L13) resolved? I could not find it in MPI.jl, LAMMPS_jll or Clang.jl .
I don't think it matters which one we use. I'm not sure why I changed them to unsigned? Perhaps changing them back to Cint would make things easier.
Okay, I ran into MethodError: Cannot convert an object of type MPI.Comm to an object of type Int32 when ccalling a function generated with Clang (based on the MPICH header) which then had Cint for the argument, and cconvert(::Type, ::MPI.Comm) fails. Perhaps
https://github.com/JuliaParallel/MPI.jl/blob/61947d925f0b5dee1c62ed1f668a77be19ee9947/src/comm.jl#L10 could be relaxed a bit? Probably that could be
Base.cconvert(::Type{T}, comm::Comm) where {T <: Integer} = convert(T, comm.val)
?
Basically, we can reuse symbols from MPI by treating MPI headers as system headers.
push!(args, "-I$(mpi_include_dir)")
to
push!(args, "-isystem$(mpi_include_dir)")
In this way, all useless symbols under mpi_include_dir will be ignored, so symbols from MPI.jl can be added on demand and you get no conflicts.
Basically, we can reuse symbols from MPI by treating MPI headers as system headers.
push!(args, "-I$(mpi_include_dir)")to
push!(args, "-isystem$(mpi_include_dir)")
Exactly what I was looking for - thanks!
Now, if I am understanding correctly, then Binary Builder ensures that an artifact matching the MPI backend selected in MPIPreferences is selected, right?
I've changed the MPICH and Microsoft MPI handles to now be signed ints (#668), I'll tag a new patch release.
It would be great to turn this discussion into some docs.