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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 and MPI.PROC_NULL
tgt = myid + 1
src = myid - 1
if myid == 0:
src = MPI.PROC_NULL
elif myid == ntasks - 1:
tgt = MPI.PROC_NULL
# Start measuring the time spent in communication
comm.barrier()
t0 = MPI.Wtime()
req_recv = comm.Irecv(buff, source=src)
req_send = comm.Isend(data, dest=tgt)
MPI.Request.Waitall((req_recv, req_send))
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]))
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))