[yt-dev] parallel_objects not freeing communicators?

[Josh Moloney]

I have a script that I'm using to perform various analysis functions on
halos from an Enzo simulation. In this script I'm using parallel_objects to
split the halos up among multiple processors.

for sto, halo in parallel_objects(halos, num_procs, storage=halo_props):
         sto.result_id = halo.id
         sto.result = analyze_halo(pf, halo, radius, old_time,
current_time, f_ej)

within analyze_halo I use WeightedAverageQuantity on a region containing
each halo, which from what I understand also uses parallel_objects.

reg = pf.h.sphere(halo.center_of_mass(),radius)
properties = {'metallicity': (reg.quantities['WeightedAverageQuantity']
    ('metallicity','Density')).in_units('Zsun')}

This works fine for a while, but after the script has analyzed several
thousand halos it eventually crashes with an MPI exception 'Too many
communicators'. I took a quick look at the code in
parallel_analysis_interface, and it seems like parallel_objects creates new
communicators with every call but never explicitly frees them. Does anyone
know if this is actually the case, or is it an issue with my script or the
mpi libraries on my machine? I'm using the experimental branch of yt-3.0.
I should be able to get this script working fairly easily by just
calculating my weighted average directly rather than calling quantities
(and I probably don't want this being done in parallel anyways since I'm
only looking at small regions), but if parallel_objects is actually leaking
communicators then it should be fixed at some point.
       - Josh
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