Java MPI in MATLAB*P Max Goldman Da Guo

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

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

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

Creating the Network 10.0.0.1 10.0.0.2 … 10.0.0.1 10.0.0.2 Problem: each node needs to know every other IP address One-time communication through frontend Each node opens a socket to every other node 10.0.0.1 10.0.0.2 …

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

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

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

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

Tests Calculate the sum of numbers 1--40000

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

Tests (cont.) Find maximum value in 40000 random numbers

Tests (cont.) “Scan” example

Demo