Firedrake-Netgen: Curved mesh creation sometimes fails in parallel

[ABaierReinio]

MFE below:

from firedrake import *
from firedrake.output import VTKFile
from netgen.occ import *

box = Box(Pnt(0, 0, 0), Pnt(1, 1, 1))
body = box.MakeFillet(box.edges, 0.1)
geo = OCCGeometry(body)
ngmesh = geo.GenerateMesh(maxh=0.1)
mesh = Mesh(Mesh(ngmesh).curve_field(2))
VTKFile("mesh.pvd").write(mesh)

Running this code in serial, the mesh is created with no issues.

But running it in parallel (e.g. mpiexec -n 2 python3 test.py) results in the following warning:

firedrake:WARNING Not able to curve element 4724, residual is: 0.18171646033208677

So it seems some of the elements are not being curved in this case.

[UZerbinati]

The fix is two-parted. You need to use PR #29 and the Netgen MR mirrored here.
Also, you need to change your code:

from firedrake import *
from firedrake.output import VTKFile
from netgen.occ import *
import netgen

if COMM_WORLD.rank == 0:
    box = Box(Pnt(0, 0, 0), Pnt(1, 1, 1))
    body = box.MakeFillet(box.edges, 0.1)
    geo = OCCGeometry(body)
    ngmesh = geo.GenerateMesh(maxh=0.1)
else:
    ngmesh = netgen.libngpy._meshing.Mesh(3)
mesh = Mesh(Mesh(ngmesh).curve_field(2))
VTKFile("mesh.pvd").write(mesh)