MPI init from Python about nrn HOT 6 CLOSED

the workhorse for transferring python objects is
destlist = pc.py_alltoall(srclist)
where the length of srclist and destlist must be pc.nhost()
None entries are allowed and a send from I to j is just that everyone except I and j fill their array
with None and the only non None object on rank I is the jth element and
https://www.neuron.yale.edu/neuron/static/py_doc/modelspec/programmatic/network/parcon.html?highlight=alltoall#ParallelContext.py_alltoall

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That suggestion is reasonable and I'll look into whether it can happen early enough in the process
of getting things properly setup. Til then you might try the environment variable
export NEURON_INIT_MPI=1

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Taking this use case a bit further, it could be interesting to support MPI actions with Python objects, namely numpy arrays.
At the moment, when doing something like

pc = h.ParallelContext()
numbers = numpy.arange(100) if pc.id() == 0 else numpy.empty(10, dtype='int32')
pc.broadcast(numbers, 0)

one gets

NEURON: object type is PythonObject instead of Vector

Would it make sense to support such use case and generally serialize Python objects for MPI actions?
@pramodk

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The ParallelContext.py_alltoall collective that takes any pickleable python object now has the
.py_[allgather, gatther, scatter, broadcast] companions.

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@nrnhines that sounds great! Thanks for the info.

Regarding the first comment, on the initialization of MPI via a specific call, any news?

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I'm toying with
test0.py

from neuron import h
pc = h.ParallelContext()
pc.mpi_init()

id = int(pc.id())
nhost = int(pc.nhost())

print ('I am %d of %d'%(id, nhost))

pc.barrier()
h.quit()

and

 mpiexec -n 2 python3 test0.py

works on the desktop with my mpich-3.3
but my openmpi 2.1.1 gives the message
(though it works with mpiexec -n 2 nrniv -python -nobanner test0.py

$ mpiexec -n 2 python3 test0.py
[hines-T7500:53222] mca_base_component_repository_open: unable to open mca_patcher_overwrite: /usr/lib/x86_64-linux-gnu/openmpi/lib/openmpi/mca_patcher_overwrite.so: undefined symbol: mca_patcher_base_patch_t_class (ignored)
...

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