[Python] Issue with MPI Communication in Python (using MPI.COMM_WORLD.isend and...

I'm working on a parallelized program using mpi4py in Python, and I'm encountering an issue where data is being sent using MPI.COMM_WORLD.isend, but when the receiving process attempts to get the data using MPI.COMM_WORLD.irecv, it ends up receiving None. I’m unsure if the communication is happening correctly or if there’s an issue with my logic.

Here’s the part of my code where the communication happens:


if self.color == 0:
current_point = self.run_MD(self.atoms, self.dyn)
i += 1
logging.info(f"Sampled point {i}.")
for dest in range(1, MPI.COMM_WORLD.Get_size()):
MPI.COMM_WORLD.isend(current_point, dest=dest, tag=0)

if req is None:
req = MPI.COMM_WORLD.irecv(source=1, tag=1)

if req.Test():
sampled_points = req.wait()
logging.info(f"Received {sampled_points}.")
req = None

elif self.color == 1:
if req is None:
req = MPI.COMM_WORLD.irecv(source=0, tag=0)

# Get the current point (blocking)
current_point = req.wait()
i += 1

if RANK == 1:
logging.info(f"Recalculating point {i} with DFT.")
sampled_points.append(self.recalc_aims(current_point))

if RANK == 1:
logging.info(f'len(sampled_points): {len(sampled_points)}')
req_send = MPI.COMM_WORLD.isend(sampled_points, dest=0, tag=1)
req_send.wait()
req = None



If I don't check using .test(), i.e. using blocking communication, everything works as intended. But somehow, even though .test() evaluates to True, color 0 only receives None for sampled_points. BTW, the communication going in this example from 0 to 1 (sending current_point) works fine.

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