I never got mpiJava to stop freezing at the MPI calls when trying to talk to a
program written in C (most likely because I don't understand mpiJava). So, I
wrapped simple openmpi commands (written in C) with Java using JNA that only
implemented some simple MPI commands... I am now able to see Java and C talk to
each other. I am interested still to hear if anybody has suggestions on how to
make a Java program communicate with a C/Fortran program via mpiJava.
Regardless, for anybody interested, the code below shows what I got working
(make sure jna-4.0.0.jar is in the same folder as these files before you run
jumptest.sh):
**IJump.java:
import com.sun.jna.Library;
import com.sun.jna.Pointer;
public interface IJump extends Library
{
void Init(int argslength, String[] args);
int WorldRank();
int WorldSize();
void Finalize();
void SendInt(int[] buf, int length, int receiver, int tag);
void RecvInt(int[] buf, int length, int receiver, int tag);
}
**Jump.java:
import com.sun.jna.Native;
public class Jump
{
private static IJump _lib = (IJump) Native.loadLibrary("jump", IJump.class);
public static void main(String args[])
{
try
{
_lib.Init(args.length, args);
int rank = _lib.WorldRank();
int size = _lib.WorldSize();
int sender = 0;
int offset = 0, cnt = 1;
int[] buf = new int[cnt];
if (rank == sender)
{
int recvr = 0;
for (int i = 1; i < size; i++)
{
if (recvr == sender)
recvr++;
buf[0] = recvr;
System.out.print("Java program is sending " + recvr + "\n");
_lib.SendInt(buf, cnt, recvr, 0);
recvr++;
}
}
else
{
System.out.print("Java program is waiting at " + rank + "\n");
_lib.RecvInt(buf, cnt, sender, 0);
}
System.out.print("Java program received " + buf[0] + " at " + rank +
"\n");
}
catch (Exception e)
{
e.printStackTrace();
}
finally
{
try
{
_lib.Finalize();
}
catch(Exception ex)
{
ex.printStackTrace();
}
}
}
}
**jump.c:
#include "mpi.h"
#include <string.h>
void Init(int argc, char *argv[])
{
MPI_Init(&argc, &argv);
}
int WorldRank()
{
int rank;
MPI_Comm_rank(MPI_COMM_WORLD, &rank);
return rank;
}
int WorldSize()
{
int size;
MPI_Comm_size(MPI_COMM_WORLD, &size);
return size;
}
void Finalize()
{
MPI_Finalize();
}
void SendInt(int *buf, int length, int receiver, int tag)
{
MPI_Send(buf, length, MPI_INT, receiver, tag, MPI_COMM_WORLD);
}
void RecvInt(int *buf, int length, int receiver, int tag)
{
MPI_Status status;
MPI_Recv(buf, length, MPI_INT, receiver, tag, MPI_COMM_WORLD, &status);
}
**interop.c:
#include "mpi.h"
#include <string.h>
int main(int argc, char *argv[])
{
int rank, size;
int i, bsize;
MPI_Status status;
int scatter = 0;
int sender = 0;
MPI_Init(&argc, &argv);
MPI_Comm_rank(MPI_COMM_WORLD, &rank);
MPI_Comm_size(MPI_COMM_WORLD, &size);
for (i = 0; i < argc; i++)
{
if (strncmp(argv[i], "-scatter", 8) == 0)
{
scatter = 1;
break;
}
}
bsize = 1;
int buf[bsize];
if (scatter)
{
int sbuf[size];
if (rank == sender)
{
printf("Scattering at %d\n", sender);
for (i = 0; i < size; i++)
sbuf[i] = i;
}
else
printf("Waiting at %d\n", rank);
MPI_Scatter(&sbuf, 1, MPI_INT32_T, &buf, 1, MPI_INT32_T, sender,
MPI_COMM_WORLD);
}
else
{
if (rank == sender)
{
int recvr = 0;
for (i = 1; i < size; i++)
{
if (recvr == sender)
recvr++;
buf[0] = recvr;
printf("C program is sending %d\n", buf[0]);
MPI_Send(&buf, 1, MPI_INT32_T, i, 0, MPI_COMM_WORLD);
recvr++;
}
}
else
{
printf("C program is waiting at %d\n", rank);
MPI_Recv(&buf, 1, MPI_INT32_T, sender, 0, MPI_COMM_WORLD, &status);
}
}
printf("C program received %d at %d\n", buf[0], rank);
MPI_Finalize();
return 0;
}
**java2c.app:
-np 1 java -jar ./Jump.jar a e io u r mine
-np 3 interop
**c2java.app:
-np 1 interop
-np 3 java -jar ./Jump.jar a e io u r mine
**Makefile:
# Created by: Andre Dozier
# Date : July 16, 2013
# Purpose : Creates two programs to test the legacy model integration tool
with various different types of interaction
#
CC = mpicc
JCC = javac
MPIJCC = mpijavac
LIB = /usr/local/lib
JNA = ./jna-4.0.0.jar
all: interop jump JumpJava
interop: interop.c
$(CC) -o interop interop.c
jump: jump.c
$(CC) -fPIC -shared -o libjump.so jump.c
JumpJava: Jump.java
$(JCC) -cp .:$(JNA) Jump.java IJump.java
**jumptest.sh:
BASEDIR=$(dirname $0)
cd $BASEDIR
echo
echo Finding source files...
find -name "*.java" > sources.txt
echo
echo Compiling code...
make -B
jar xf jna-4.0.0.jar
# javac -cp $HOME/extras/jna-4.0.0.jar:. @sources.txt
echo
echo Packaging code into Jar files...
echo Main-Class: Jump > manifest.txt
jar cfm Jump.jar manifest.txt IJump.class Jump.class libjump.so com
echo
echo Removing temporary files...
rm sources.txt manifest.txt
rm -rf com META-INF
find -name "*.class" | xargs rm -rf
echo
echo Testing Java to C MPI connection
mpirun --app java2c.app
echo
echo Testing C to Java MPI connection
mpirun --app c2java.app
echo
André
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