[Paraview] [Catalyst] Setting the MPI Comm in Python

Wed Mar 9 05:34:46 EST 2016

Hi Andy,

Thank you for your feedback, it helped me solve my problem.

If anyone is having a similar problem, what I ended up doing is:

import mpi4py.MPI as MPI

import vtk

comm = MPI.COMM_WORLD

rank = comm.Get_rank()

size = comm.Get_size()

in_subcomm = [0,3,6,9] # list of ranks to include in the VTK communicator

subcomm = comm.Split(1 if rank in in_subcomm else 0,rank)

#--- In another part of the program called only by the procs in in_subcomm

vtkComm = vtk.vtkMPI4PyCommunicator.ConvertToVTK(subcomm)

vtkCont = vtk.vtkMPIController()

vtkCont.SetCommunicator(vtkComm)

vtk.vtkMPIController.SetGlobalController(vtkCont)

Due to the way my application works, I had to split the communicator myself, i.e. without using CreateSubController() or PartitionController() because vtk is loaded only by some procs and not every single one (a Mpi_Comm_split operation would therefore be impossible to do).

--

Yohann

From: Andy Bauer [mailto:andy.bauer at kitware.com] 
Sent: Sunday, March 06, 2016 12:55 PM
To: VAUTRIN Yohann (SAFRAN)
Cc: paraview at paraview.org
Subject: Re: [Paraview] [Catalyst] Setting the MPI Comm in Python

Hi,

Can you use a different controller that has the same MPI processes assigned to it? If that works for you, you should be able to just create a vtkMPIController and use either CreateSubController() or PartitionController() to create one similar to what you want. Note that you may need to create two vtkMPIControllers, one that corresponds to MPI_COMM_WORLD and one for your partitioning. After you've done that you can use the vtkMPIController::SetGlobalController() to have VTK and ParaView use that for interprocess communication.

Best,

Andy

On Fri, Feb 26, 2016 at 10:09 AM, VAUTRIN Yohann (SAFRAN) <yohann.vautrin at safran.fr> wrote:

Hi,

I’m working on a Catalyst adaptor written in Python for one of the CFD codes I use at work and I’m having trouble setting the MPI communicator I want the vtkCPProcessor object to use (in order to use a subset of MPI_COMM_WORLD). The MPI communicator I create is a mpi4py.MPI_Comm object, which I convert to a vtkMPICommunicator object using vtk.vtkMPI4PyCommunicator.ConvertToVTK. However vtk.vtkPVCatalystPython.vtkCPProcessor.Initialize is expecting a vtkMPICommunicatorOpaqueComm object and there does not seem to be a way for me to create such an object from the Python interface. Am I missing something here or is something not wrapped correctly or wrong?

For the moment I use mpi4py.MPI.COMM_WORLD to test everything. The following minimal example replicates my problem:

import mpi4py.MPI

import vtk

comm = mpi4py.MPI.COMM_WORLD

coprocessor = vtk.vtkPVCatalystPython.vtkCPProcessor()

coprocessor.Initialize(vtk.vtkMPI4PyCommunicator.ConvertToVTK(comm))

The last line fails with this message:

TypeError: Initialize argument 1: method requires a vtkMPICommunicatorOpaqueComm, a vtkMPICommunicator was provided.

I hope I post on the right mailing list as this could actually be a problem in VTK.

Thank you for your help.

Best,

Yohann V.

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