1. Java MPI in MATLAB*P
Max Goldman Da Guo

2. Overview Allow nodes to communicate during mm mode computation
Implement MPI primitives in Java
Interface to these methods in MATLAB*P
Why Java?
MATLAB already runs a JVM
Java well suited to network programming

3. Results Basic implementation that works
And some not-so-basic things that work
Performance looks promising
Error handling needs improvement
Some quirks

4. Basic Architecture Node 0 MATLAB Node 1 Node … mm mode Frontend MATLAB
Backend
C/C++
JVM
Java sockets

5. Creating the Network …
Problem: each node needs to know every other IP address
One-time communication through frontend
Each node opens a socket to every other node …

6. Passing Data Java functions operate on double[] buffers
Conversion is done automagically
Pass-by-value across the Java-MATLAB interface, so methods return buffers
In MPI spec, functions take output pointers
Everything comes back as a column!
Didn’t want to add another wrapper, so users must use columns or reshape themselves

7. Making the Call mmpi(fname, varargin)
Function fname can contain MPI calls
Will be passed directly to mm(…)
Forces MPI to be separated from *p code
Eliminates confusion due to e.g. different indexing
Can use mmpi(…) any number of times
Function does not have to go all the way from init to fnlz

8. Making the Call Part II Inside mmpi Then pass control to mm
First check network, build if needed
Then pass control to mm
function result = simpletest(arg)
import mpi.*;
MPI.init;
if MPI.COMM_WORLD.rank == 0;
data = [42];
MPI.COMM_WORLD.send(data, 1, 1, 13);
result = 0;
elseif MPI.COMM_WORLD.rank == 1
got = MPI.COMM_WORLD.recv(1, 0, 13);
result = got(1);
end
MPI.fnlz;
Quirks

9. MPI Functions (Methods)
Class MPI
init and fnlz – “finalize” reserved in Java
Class Comm (MPI.COMM_WORLD)
send – basic send
recv – basic receive
bcast
reduce
scatter
gather
scan – uses parallel prefix }
use a binary tree algorithm

10. Tests
Calculate the sum of numbers

11. Tests (cont.)
Find the approximate value of Pi =

12. Tests (cont.)
Find maximum value in random numbers

13. Tests (cont.)
“Scan” example

14. Demo