HDF5 fluxes file not written during a set of parallel simulations

[ilicog]

When running a set of parallel meep simulations, HDF5 flux output won't write when the sim.use_output_directory options is specified. MWE below:

import meep as mp

def main(group):
    a = 1
    tabs = 2
    tair = 2
    sz = 2*(tabs+tair)
    cell_size = mp.Vector3(a,a,sz)

    pml_layers = [mp.PML(thickness=tabs,direction=mp.Z,side=mp.High),
                  mp.Absorber(thickness=tabs,direction=mp.Z,side=mp.Low)]

    fcen = 1
    df = 0.5
    geometry = []
    src_pos = 0.5*sz-tabs-0.2*tair
    sources = [ mp.Source(mp.GaussianSource(fcen, fwidth=df), component=mp.Ey, center=mp.Vector3(0,0,src_pos),
                          size=mp.Vector3(a,a,0)) ]
    sim = mp.Simulation(cell_size=cell_size,
                        geometry=geometry,
                        sources=sources,
                        boundary_layers=pml_layers,
                        resolution=10)

    nfreq = 10
    refl = sim.add_flux(fcen, df, nfreq, mp.FluxRegion(center=mp.Vector3(0,0,+0.5*sz-tabs-0.5*tair),size=mp.Vector3(a,a,0)))
    sim.run(until=10)

    sim.use_output_directory("out_{}".format(group)) # <--- this causes issues when Ngroups > 1
    sim.save_flux('refl-flux', refl)
    
Ngroups = 4
group = mp.divide_parallel_processes(Ngroups)

main(group)

This is run via

mpirun -np 12 python test.py

Error message:

creating output file "out_0/test-refl-flux.h5"...
HDF5-DIAG: Error detected in HDF5 (1.10.4) MPI-process 3:
#000: H5F.c line 444 in H5Fcreate(): unable to create file
major: File accessibilty
minor: Unable to open file
#1: H5Fint.c line 1364 in H5F__create(): unable to open file
major: File accessibilty
minor: Unable to open file
#2: H5Fint.c line 1548 in H5F_open(): unable to open file: name = 'out_1/test-refl-flux.h5', tent_flags = 13

When Ngroups=1, the h5 file is written in the output directory just fine.

[ReDoDx09]

Hello @ilicog
did you find the solution ?