Simple exercise for exchanging messages with two processes

message-exchange/LICENSE.txt

+
+Copyright (C) 2018  CSC - IT Center for Science Ltd.
+
+Licensed under the terms of the GNU General Public License as
+published by the Free Software Foundation, either version 3 of the
+License, or (at your option) any later version.
+
+Code is distributed in the hope that it will be useful, but WITHOUT
+ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+for more details.
+
+Copy of the GNU General Public License can be obtained from
+<http://www.gnu.org/licenses/>.
+

message-exchange/README.md

+## Simple message exchange
+
+a) Write a simple program where two processes send and receive a
+message to/from each other using `MPI_Send` and `MPI_Recv`. The message
+content is an integer array, where each element is initialized to the
+rank of the process. After receiving a message, each process should
+print out the rank of the process and the first element in the
+received array. You may start from scratch or use as a starting point
+the skeleton code found in [exchange.c](exchange.c), 
+[exchange.F90](exchange.F90) or [exchange.py](exchange.py)
+
+b) Increase the message size to 100,000, recompile and run. It is very likely
+that the program will dead lock, try to figure out reason for this, and
+how to resolve it.

message-exchange/exchange.F90

+program exchange
+  use mpi
+  implicit none
+  integer, parameter :: size = 100
+  integer :: rc, myid, ntasks, count
+  integer :: status(MPI_STATUS_SIZE)
+  integer :: message(size)
+  integer :: receiveBuffer(size)
+
+  call mpi_init(rc)
+  call mpi_comm_rank(MPI_COMM_WORLD, myid, rc)
+  call mpi_comm_size(MPI_COMM_WORLD, ntasks, rc)
+
+  message = myid
+
+  ! TODO: Implement sending and receiving as defined in the assignment
+  if ( myid == 0 ) then
+
+     write(*,'(A10,I3,A10,I3)') 'Rank: ', myid, &
+          ' received ', receiveBuffer(1)
+  else if (myid == 1) then
+
+     write(*,'(A10,I3,A10,I3)') 'Rank: ', myid, &
+          ' received ', receiveBuffer(1)
+  end if
+
+  call mpi_finalize(rc)
+
+end program exchange

message-exchange/exchange.c

+#include<stdio.h>
+#include<stdlib.h>
+#include<mpi.h>
+
+
+int main(int argc, char *argv[])
+{
+    int i, myid, ntasks;
+    int size = 100;
+    int *message;
+    int *receiveBuffer;
+    MPI_Status status;
+
+    MPI_Init(&argc, &argv);
+    MPI_Comm_size(MPI_COMM_WORLD, &ntasks);
+    MPI_Comm_rank(MPI_COMM_WORLD, &myid);
+
+    /* Allocate message */
+    message = malloc(sizeof(int) * size);
+    receiveBuffer = malloc(sizeof(int) * size);
+    /* Initialize message */
+    for (i = 0; i < size; i++) {
+        message[i] = myid;
+    }
+
+    /* TODO: */
+    /* Send and receive messages as defined in exercise */
+    if (myid == 0) {
+
+        printf("Rank %i received %i\n", myid, receiveBuffer[0]);
+    } else if (myid == 1) {
+
+        printf("Rank %i received %i\n", myid, receiveBuffer[0]);
+    }
+
+    free(message);
+    free(receiveBuffer);
+    MPI_Finalize();
+    return 0;
+}

message-exchange/exchange.py

+from __future__ import print_function
+from mpi4py import MPI
+import numpy
+
+comm = MPI.COMM_WORLD
+rank = comm.Get_rank()
+
+# Simple message exchange using numpy arrays
+n = 100000
+data = numpy.zeros(n, int) + rank
+buff = numpy.empty(n, int)
+
+# TODO:
+# Send and receive messages as defined in exercise
+if rank == 0:
+
+elif rank == 1:
+
+
+print("Rank {0} received an array filled with {1}s.".format(rank, buff[0]))
+
+
+# Simple message exchange of Python objects
+meta = {'rank': rank}
+
+# TODO:
+# Send and receive messages as defined in exercise
+if rank == 0:
+
+elif rank == 1:
+
+
+print("Rank {0} received a message from rank {1}.".format(rank, msg['rank']))
+

message-exchange/solution/exchange.F90

+program exchange
+  use mpi
+  implicit none
+  integer, parameter :: size = 100000
+  integer :: rc, myid, ntasks, count
+  integer :: status(MPI_STATUS_SIZE)
+  integer :: message(size)
+  integer :: receiveBuffer(size)
+
+  call mpi_init(rc)
+  call mpi_comm_rank(MPI_COMM_WORLD, myid, rc)
+  call mpi_comm_size(MPI_COMM_WORLD, ntasks, rc)
+
+  message = myid
+
+  ! Send and receive as defined in the assignment
+  if ( myid == 0 ) then
+     call mpi_send(message, size, MPI_INTEGER, 1, &
+          1, MPI_COMM_WORLD, rc)
+     call mpi_recv(receiveBuffer, size, MPI_INTEGER, 1,  &
+          2, MPI_COMM_WORLD, status, rc)
+     write(*,'(A10,I3,A10,I3)') 'Rank: ', myid, &
+          ' received ', receiveBuffer(1)
+  else if (myid == 1) then
+      ! One MPI tasks needs to start with send and the other one with
+      ! receive, otherwise the program dead locks with large message
+      ! sizes in most MPI implementations 
+     call mpi_recv(receiveBuffer, size, MPI_INTEGER, 0,  &
+          1, MPI_COMM_WORLD, status, rc)
+     call mpi_send(message, size, MPI_INTEGER, 0, &
+          2, MPI_COMM_WORLD, rc)
+     write(*,'(A10,I3,A10,I3)') 'Rank: ', myid, &
+          ' received ', receiveBuffer(1)
+  end if
+
+  call mpi_finalize(rc)
+
+end program exchange

message-exchange/solution/exchange.c

+#include<stdio.h>
+#include<stdlib.h>
+#include<mpi.h>
+
+
+int main(int argc, char *argv[])
+{
+    int i, myid, ntasks;
+    int size = 100000;
+    int *message;
+    int *receiveBuffer;
+    MPI_Status status;
+
+    MPI_Init(&argc, &argv);
+    MPI_Comm_size(MPI_COMM_WORLD, &ntasks);
+    MPI_Comm_rank(MPI_COMM_WORLD, &myid);
+
+    /* Allocate message */
+    message = malloc(sizeof(int) * size);
+    receiveBuffer = malloc(sizeof(int) * size);
+    /* Initialize message */
+    for (i = 0; i < size; i++) {
+        message[i] = myid;
+    }
+
+    /* Send and receive messages as defined in exercise */
+    if (myid == 0) {
+        MPI_Send(message, size, MPI_INT, 1, 1, MPI_COMM_WORLD);
+        MPI_Recv(receiveBuffer, size, MPI_INT, 1, 2, MPI_COMM_WORLD,
+                 MPI_STATUS_IGNORE);
+        printf("Rank %i received %i\n", myid, receiveBuffer[0]);
+    } else if (myid == 1) {
+        /* One MPI tasks needs to start with send and the other one with
+         * receive, otherwise the program dead locks with large message
+         * sizes in most MPI implementations */
+        MPI_Recv(receiveBuffer, size, MPI_INT, 0, 1, MPI_COMM_WORLD,
+                 MPI_STATUS_IGNORE);
+        MPI_Send(message, size, MPI_INT, 0, 2, MPI_COMM_WORLD);
+        printf("Rank %i received %i\n", myid, receiveBuffer[0]);
+    }
+
+    free(message);
+    free(receiveBuffer);
+    MPI_Finalize();
+    return 0;
+}

message-exchange/solution/exchange.py

+from __future__ import print_function
+from mpi4py import MPI
+import numpy
+
+comm = MPI.COMM_WORLD
+rank = comm.Get_rank()
+
+# Simple message exchange
+meta = {'rank': rank}
+
+if rank == 0:
+    comm.send(meta, dest=1)
+    msg = comm.recv(source=1)
+elif rank == 1:
+    msg = comm.recv(source=0)
+    comm.send(meta, dest=0)
+print("Rank {0} received a message from rank {1}.".format(rank, msg['rank']))
+
+# Simple message exchange using numpy arrays
+n = 100000
+data = numpy.zeros(n, int) + rank
+buff = numpy.empty(n, int)
+
+if rank == 0:
+    comm.Send(data, dest=1)
+    comm.Recv(buff, source=1)
+elif rank == 1:
+    # One MPI tasks needs to start with send and the other one with
+    # receive, otherwise the program dead locks with large message
+    # sizes in most MPI implementations 
+    comm.Recv(buff, source=0)
+    comm.Send(data, dest=0)
+print("Rank {0} received an array filled with {1}s.".format(rank, buff[0]))
+