spotpy: Bug: sceua gets stuck with MPI after burn-in

Hey there,

from spotpy 1.5.0 on, sce optimization with MPI get stuck after the burn in phase. Here is a minimal example:

from spotpy.algorithms import sceua
from spotpy.examples.spot_setup_rosenbrock import spot_setup
setup = spot_setup("sceua")  # spot_setup() for spotpy 1.4.6
sampler = sceua(setup, parallel="mpi", dbname='db', dbformat="csv")
sampler.sample(repetitions=10000, ngs=4)

Running with

mpiexec -n 4 python3 test.py

Gives the following output:

Initializing the  Shuffled Complex Evolution (SCE-UA) algorithm  with  10000  repetitions
The objective function will be minimized
Initializing the  Shuffled Complex Evolution (SCE-UA) algorithm  with  10000  repetitions
The objective function will be minimized
Initializing the  Shuffled Complex Evolution (SCE-UA) algorithm  with  10000  repetitions
The objective function will be minimized
Initializing the  Shuffled Complex Evolution (SCE-UA) algorithm  with  10000  repetitions
The objective function will be minimized
Starting burn-in sampling...
Initialize database...
['csv', 'hdf5', 'ram', 'sql', 'custom', 'noData']
* Database file 'db.csv' created.
Burn-in sampling completed...
Starting Complex Evolution...
ComplexEvo loop #1 in progress...

And from there on, nothing more happens. With parallel="seq" it takes about 5 seconds to finish. Do you know what the problem could be?

I’ve got mpi4py 3.0.2 installed and I am using Python 3.6.8. With spotpy 1.4.6 everything is working. From 1.5.0 on the above mentioned behavior occurs.

Cheers, Sebastian