Python: Using mpi4py to bcast an array to other scripts with spawn

Question

I'm trying to write two scripts, one a master and one a worker, where the master script will spawn multiple processes of the worker and then bcast a numpy array to the worker spawns. From looking at the number of (vague) tutorials online for mpi4py, I feel like I understand this concept, but any test code I've written won't successfully send the array to the workers. I don't get errors, but they never receive the array.

Can someone please give me a clear example of how to use mpi4py, spawn, and bcast to broadcast an array to a number of spawned worker scripts? Thank you!

UPDATE: Example:

Master script:

#! /usr/bin/env python
# master test

import sys,time
from mpi4py import MPI
import numpy as np

comm2    = MPI.COMM_WORLD
rank     = comm2.Get_rank()
mpisize  = comm2.Get_size()

initcomm = MPI.COMM_SELF.Spawn(sys.executable, \
                           args=['test2.py'], \
                           maxprocs=5)

# Initialise the programs
test = np.array([1,2,3], 'i')
print("About to broadcast {0} from rank {1}".format(test, rank))
initcomm.Bcast([test, MPI.INT], root=0)
initcomm.Disconnect()

Worker script:

#! /usr/bin/env python
# child test

import sys,time
from mpi4py import MPI
import numpy as np

comm2    = MPI.COMM_WORLD
rank     = comm2.Get_rank()
mpisize  = comm2.Get_size()

initcomm = MPI.Comm.Get_parent()

test = np.zeros(3, 'i')
print("Bcast coming to rank {0}".format(rank))
initcomm.Bcast([test, MPI.INT], root=0)
print("Received {0}".format(test))
initcomm.Disconnect()

Answer 1

You need to change Bcast in the master script to:

initcomm.Bcast([test, MPI.INT], root=MPI.ROOT)

If it's set to 0 , the master will think that the root is rank 0 in the remote/worker group, and the program will hang.