[Paraview] MPI-aware reader plugin only has rank 0

[Schlottke, Michael]

> are you sure you don't mean that only printf/std:::cout from rank 0 is visible?
I also thought that it might be a visibility issue, thus I opened a file with std::ofstream on each rank with the rank id encoded in the filename. Only one file ever gets created, though, and it is the one with “0” in the name.

> but I actual fact the other pvservers are fine. Create a sphere and check if it has N pieces.
I did that and visualized it by vtkProcessId. The number of ids indeed matches the number of ranks, so I guess nothing fundamental is wrong with the MPI use within ParaView. I just can’t fathom why the reader plugin does not run in parallel. Just to be sure, I added a call 

MPI_Barrier(MPI_COMM_WORLD);

in RequestData and indeed, ParaView gets stuck there, as apparently the collective call is never issued from any rank != 0.

Michael