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from __future__ import print_function
from mpi4py import MPI
import numpy
from sys import stdout
comm = MPI.COMM_WORLD
myid = comm.Get_rank()
ntasks = comm.Get_size()
# Send and receive buffers
n = 10000000
data = numpy.zeros(n, int) + myid
buff = numpy.zeros(n, int)
# Message chain using Sendrecv
# Start measuring the time spent in communication
comm.barrier()
t0 = MPI.Wtime()
tgt = myid + 1
src = myid - 1
if myid > 0 and myid < ntasks -1: # middle of chain; send and receive
comm.Sendrecv(data, dest=tgt, sendtag=tgt,
recvbuf=buff, source=src, recvtag=myid)
print(" Rank {0}: sent {1} elements to myid {2}.".format(myid, len(data), tgt))
print(" Rank {0}: received a message from myid {1}.".format(myid, src))
print(" Rank {0}: received an array filled with {1}s.".format(myid, buff[0]))
elif myid == 0: # start of chain; only send
comm.Send(data, dest=tgt, tag=tgt)
print(" Rank {0}: sent {1} elements to myid {2}.".format(myid,
len(data), tgt))
elif myid == ntasks - 1: # end of chain; only receive
comm.Recv(buff, source=src, tag=myid)
print(" Rank {0}: received a message from myid {1}.".format(myid, src))
print(" Rank {1}: received an array filled with {1}s.".format(myid, buff[0]))
t1 = MPI.Wtime()
# ... wait for every myid to finish ...
stdout.flush()
comm.barrier()
if myid == 0:
print("")
print("Timings")
print("Time elapsed in myid {0} {1:6.3f}".format(myid, t1 - t0))
stdout.flush()
comm.barrier()
if myid == ntasks - 1:
print("Time elapsed in myid {0} {1:6.3f}".format(myid, t1 - t0))