python MPI sendrecv() to pass a python object

问题:

I am trying to use mpi4py's sendrecv() to pass a dictionary obj.

from mpi4py import MPI
comm=MPI_COMM_WORLD
rnk=comm.Get_rank()
size=comm.Get_size()

idxdict={1:2}
buffer=None
comm.sendrecv(idxdict,dest=(rnk+1)%size,sendtag=rnk,recvobj=buffer,source=(rnk-1+size)%size,recvtag=(rnk-1+size)%size)
idxdict=buffer

If I print idxidctat the last step, I will get a bunch of "None"s, so the dictionary idxdict is not passed between cores. If I use a dictionary as buffer: buffer={}, then there is typeerror:TypeError: expected a writeable buffer object.

What did I do wrong? Many thanks for your help.

回答1:

I believe the documentation is misleading here; sendrecv returns the received buffer, and doesn't use the receive object argument at all that I can see (at least in older versions, 1.2.x). So your above code doesn't work (although the receive does in fact happen), but the below does:

from mpi4py import MPI
comm=MPI.COMM_WORLD
rnk=comm.Get_rank()
size=comm.Get_size()

idxdict={1:2}
buffer = comm.sendrecv(sendobj=idxdict,dest=(rnk+1)%size,source=(rnk-1+size)%size)

print "idxdict = ", idxdict
print "buffer = ", buffer