Julia with MPI

Parellel computing of Julia

A short note on how to configure open-mpi package for parellel computing of Julia on os x (as of 2025/01/19).

1. Install open-mpi

# using homebrew
brew install --build-from-source openmpi

It installed open-mpi with version 5.0.6.

2. Specifying the path to the mpi library

We need to set DYLD_FALLBACK_LIBRARY_PATH in the shell profile file. I am using zshell, so I added the following line in .zshrc.

# in .zshrc file, add
export DYLD_FALLBACK_LIBRARY_PATH="/opt/homebrew/Cellar/open-mpi/5.0.6/lib"

Then do the following in the shell prompt to apply this change.

> source ~/.zshrc

3. Add MPI/MPIPreferences package in Julia

# tested with julia v1.11.2
julia

After Julia being launched, go to the package mode by pressing ] key. Then,

(@v1.11) pkg> add MPI
(@v1.11) pkg> add MPIPreferences

Once the package is installed, come out from this package mode to julia by hitting ctrl + C. Then configure the open-mpi for Julia.

julia> using MPIPreferences
julia> MPIPreferences.use_system_binary()

This will print out some information regarding open-mpi. Since we want to use open-mpi, do the following.

julia> MPIPreferences.use_jll_binary("OpenMPI_jll")

4. Perform a test

Now, we can test whether parellel computing in Julia is working or not by executing the following simple script.

# mpitest.jl
using MPI
MPI.Init()

comm = MPI.COMM_WORLD
print("Hello world, I am rank $(MPI.Comm_rank(comm)) of $(MPI.Comm_size(comm))\n")
MPI.Barrier(comm)

Then in the shell prompt,

> mpirun -n 4 julia mpitest.jl
Hello world, I am rank 1 of 4
Hello world, I am rank 2 of 4
Hello world, I am rank 0 of 4
Hello world, I am rank 3 of 4

[Optional] Create Julia wrapper

Julia wrapper can be an alternative way for the parellel computing for Julia. It can be easily installed in Julia.

$ julia
julia> using MPI
julia> MPI.install_mpiexecjl()

This will create mpiexecjl in your Julia’s bin directory (maybe in ~/.julia/bin). You may create the symbolic link of this executable file in your system.

> sudo ln -s  ~/.julia/bin/mpiexecjl /usr/local/bin/

Then check whether this works in the shell prompt,

> mpiexecjl -n 4 julia mpitest.jl
Hello world, I am rank 1 of 4
Hello world, I am rank 2 of 4
Hello world, I am rank 0 of 4
Hello world, I am rank 3 of 4

For more detail, please refer to the documentation of MPI.jl