python problem with MPI (mpi4py), client can not connect

Question

The error I'm getting is:

Traceback (most recent call last): File "client2.py", line 14, in port = MPI.Lookup_name(service, info) File "Comm.pyx", line 1676, in mpi4py.MPI.Lookup_name (src/mpi4py.MPI.c:64562) mpi4py.MPI.Exception: MPI_ERR_NAME: invalid name argument

I am trying implement client/server model using mpi4py. Server can Publish_name and waits for clients. However, client can not use the necessary method described in the api as shown below:

#! /usr/bin/env python

from mpi4py import MPI

rank = MPI.COMM_WORLD.Get_rank()

def log(msg, *args):
    if rank == 0:
        print msg % args

info = MPI.INFO_NULL
service = 'pyeval'
log("looking-up service '%s'", service)
port = MPI.Lookup_name(service, info) // PROBLEM HERE !
log("service located  at port '%s'", port)

root = 0
log('waiting for server connection...')
comm = MPI.COMM_WORLD.Connect(port, info, root)
log('server connected...')

while True:
    done = False
    if rank == root:
        try:
            message = raw_input('pyeval>>> ')
            if message == 'quit':
                message = None
                done = True
        except EOFError:
            message = None
            done = True
        comm.Send(message, dest=0, tag=0)
   else:
        message = None
    done = MPI.COMM_WORLD.Bcast(done, root)
    if done:
        break

log('disconnecting server...')
comm.Disconnect()

I am also posting the server side code, as it might help:

#! /usr/bin/env python

from mpi4py import MPI

rank = MPI.COMM_WORLD.Get_rank()

def log(msg, *args):
    if rank == 0:
        print msg % args


log('')

info = MPI.INFO_NULL

port = MPI.Open_port(info)
log("opened port: '%s'", port)

service = 'pyeval'
MPI.Publish_name(service, info, port)
log("published service: '%s'", service)

root = 0
log('waiting for client connection...')
comm = MPI.COMM_WORLD.Accept(port, info, root)
log('client connected...')

while True:
    done = False
    if rank == root:
        message = comm.Recv(source=0, tag=0)
        if message is None:
            done = True
        else:
            try:
                print 'eval(%r) -> %r' % (message, eval(message))
            except StandardError:
                print "invalid expression: %s" % message
    done = MPI.COMM_WORLD.Bcast(done, root)
    if done:
        break

log('disconnecting client...')
comm.Disconnect()

log('upublishing service...')
MPI.Unpublish_name(service, info, port)

log('closing port...')
MPI.Close_port(port)

Answer 1

I needed to use ompi-server for name publishing and name look ups. Following steps for executing server and client worked for me:

ompi-server

rm -f /tmp/ompi-server.txt
killall ompi-server
ompi-server -r /tmp/ompi-server.txt

server

mpiexec --ompi-server file:/tmp/ompi-server.txt -n 1 python server.py

client

mpiexec --ompi-server file:/tmp/ompi-server.txt -n 1 python client.py

Answer 2

You want the server to spawn the clients so that they can communicate. Also, your Send/Recv/Bcasts should be send/recv/bcast ; mpi4py supports both Send and send, Recv and recv, etc, but the upper case versions take "regular" C/C++/Fortran arguments, and the lowercase ones are more pythonic.

So the following succesfully runs for me - client.py:

#! /usr/bin/env python
from mpi4py import MPI

rank = MPI.COMM_WORLD.Get_rank()

def log(msg, *args):
    if rank == 0:
        print msg % args

info = MPI.INFO_NULL
service = "pyeval"
log("looking-up service '%s'", service)
port = MPI.Lookup_name(service)
log("service located  at port '%s'", port)

root = 0
log('waiting for server connection...')
comm = MPI.COMM_WORLD.Connect(port, info, root)
log('server connected...')

while True:
    done = False
    if rank == root:
        try:
            message = raw_input('pyeval>>> ')
            if message == 'quit':
                message = None
                done = True
        except EOFError:
            message = None
            done = True
        comm.send(message, dest=0, tag=0)
    else:
        message = None
    done = MPI.COMM_WORLD.bcast(done, root)
    if done:
        break

log('disconnecting server...')
comm.Disconnect()

and server.py:

#! /usr/bin/env python

from mpi4py import MPI

rank = MPI.COMM_WORLD.Get_rank()

def log(msg, *args):
    if rank == 0:
        print msg % args

log('')

info = MPI.INFO_NULL

port = MPI.Open_port(info)
log("opened port: '%s'", port)

service = 'pyeval'
MPI.Publish_name(service, info, port)
log("published service: '%s'", service)

MPI.COMM_WORLD.Spawn("./client.py", maxprocs=1)

root = 0
log('waiting for client connection...')
comm = MPI.COMM_WORLD.Accept(port, info, root)
log('client connected...')

while True:
    done = False
    if rank == root:
        message = comm.recv(source=0, tag=0)
        if message is None:
            done = True
        else:
            try:
                print 'eval(%r) -> %r' % (message, eval(message))
            except StandardError:
                print "invalid expression: %s" % message
    done = MPI.COMM_WORLD.bcast(done, root)
    if done:
        break

log('disconnecting client...')
comm.Disconnect()

log('upublishing service...')
MPI.Unpublish_name(service, info, port)

log('closing port...')
MPI.Close_port(port)

But here you'll also have to deal with the fact that most MPI implementations will only give stdin to rank 0, so the clients don't have a nice way to get input from a terminal (in general, how would that work if there were multiple clients?)