[Numpy-discussion] MPI: Sendrecv blocks

[Florian Lindner]

Hello,

I have this piece of code:

comm = MPI.COMM_WORLD
temp = np.zeros(blockSize*blockSize)
PrintNB("Communicate A to", get_left_rank())
comm.Sendrecv(sendbuf=np.ascontiguousarray(lA), dest=get_left_rank(), 
recvbuf=temp)
lA = np.reshape(temp, (blockSize, blockSize))
PrintNB("Finished sending")


lA being a numpy array. Output is:

[0] Communicate A to 1
[2] Communicate A to 3
[3] Communicate A to 2
[1] Communicate A to 0
[1] Finished sending
# here it blocks

[n] is the rank. I have a circular send. 0>1, 1>0 and 2>3, 3>2. I understood 
Sendrec so that it is made specifically for these cases, but still it 
blocks.

What is the problem here?

Thanks!
Florian