I converted the ring_c.c code from OPENMPI examples in python to experiment with mpi4py. Here is my code.
from mpi4py import MPI
comm = MPI.COMM_WORLD
rank = comm.Get_rank()
size = comm.Get_size()
next_proc = (rank + 1) % size
prev_proc = (rank + size - 1) % size
tag = 2
message = 10
if 0 == rank:
comm.send(message, dest=next_proc, tag=tag)
while(1):
message = comm.recv(message, source=prev_proc, tag=tag)
comm.Recv_init
if 0 == rank:
message = message - 1
print "Process %d decremented value: %d\n" %(rank, message)
comm.send(message, dest=next_proc, tag=tag)
if 0 == message:
print "Process %d exiting\n" %(rank)
break;
if 0 == rank:
message = comm.recv(message, source=prev_proc, tag=tag)
When I run it via mpiexec for any number of processes, for example
mpiexec -n 10 python ring_py.py
It gives the following output and error:
Process 0 decremented value: 9
Process 0 decremented value: 8
Process 0 decremented value: 7
Process 0 decremented value: 6
Process 0 decremented value: 5
Process 0 decremented value: 4
Traceback (most recent call last):
File "ring_py.py", line 20, in <module>
message = comm.recv(message, source=prev_proc, tag=tag)
File "MPI/Comm.pyx", line 1192, in mpi4py.MPI.Comm.recv (src/mpi4py.MPI.c:106889)
File "MPI/msgpickle.pxi", line 287, in mpi4py.MPI.PyMPI_recv (src/mpi4py.MPI.c:42965)
mpi4py.MPI.Exception: MPI_ERR_TRUNCATE: message truncated
A couple of observations
A few details about my system.
Can someone please help me understand what is going on with my code.
Thank you, Jayant
I tried your code and I got an error at:
message = comm.recv(message, source=prev_proc, tag=tag)
Stating:
TypeError: expected a writeable buffer object
Following the tutorial of mpi4py or MPI4Py causes error on send/recv , I successfully tried:
message = comm.recv( source=prev_proc, tag=tag)