# MPI.jl - Different behaviors using MPIManager and mpirun

**URL:** https://discourse.julialang.org/t/mpi-jl-different-behaviors-using-mpimanager-and-mpirun/19758
**Category:** Julia at Scale
**Created:** [January 17, 2019, 8:01pm UTC](https://discourse.julialang.org/t/mpi-jl-different-behaviors-using-mpimanager-and-mpirun/19758 "2019-01-17T20:01:39Z")
**Posts on this page:** 1
**Page:** 1

<div class="post-metadata">

### Author: ![jalving](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/jalving/32/2826_2.png) [@jalving](https://discourse.julialang.org/u/jalving)
#### Post date: [January 17, 2019, 8:01pm UTC](https://discourse.julialang.org/t/mpi-jl-different-behaviors-using-mpimanager-and-mpirun/19758/1 "2019-01-17T20:01:39Z")

</div>

I’m getting some interesting behavior using the MPIManager with a parallel optimization solver and I’m trying to rule out whether the MPIManager is doing something different than just using MPI.Init() and running with my system mpirun.

When I use the MPIManager, my solver works and scales how I would expect with more cpus (this is great!). When I use mpirun and execute my script, the solver stalls immediately and eventually fails.

Example with MPIManager:  
script1.jl

```julia
using MPI
include("my_model_stuff.jl")

manager = MPIManager(np = 2)
addprocs(manager)

my_model = create_my_model()
send_model_to_mpi_ranks(my_model) #this uses a RemoteChannel and @spawnat to send my_model to each rank from manager.mpi2j. It is called my_model on each rank.
MPI.@mpi_do manager solve(my_model) #solves the model with my MPI solver. 

```

Then I run the script

```julia
$ julia script1.jl # solver succeeds! Solver recognizes 2 ranks.

```

Example without MPIManager  
script2.jl

```julia
using MPI
include("my_model_stuff.jl")

MPI.Init()
my_model = create_my_model()
solve(my_model) 
MPI.Finalize()

```

Now run the script with mpirun

```julia
$ mpirun -np 2 <path to julia> script2.jl #solver fails. It also recognizes the 2 ranks.

```

Both cases work with -np 1, so I think it has to be something to do with MPI. Is there something fundamentally different with how MPIManager sets up the workers? I looked through its source code, but nothing particularly jumps out at me.

I’m using Julia 1.0.3 and mpich2 v3.2. Both `which(mpirun) `, `which(mpicc)` and the Julia build script point to the same locations.