1. Aamir Shafi, Bryan Carpenter, Mark Baker
MPJ Express: An Implementation of MPI in Java Version: 0.35 (Beta Release)
Aamir Shafi, Bryan Carpenter, Mark Baker
4/15/2017

2. The current release contains:
Introduction
MPJ Express is a message passing library that be can be used by the application developers to develop and execute parallel Java applications on compute clusters or network of computers.
MPJ Express is originally designed for distributed memory machines like clusters but also supports efficient execution of parallel applications on desktops or laptops that contain shared memory or multicore processors
MPJ Express is a reference implementation of mpiJava 1.2 API, which is an MPI-like API for Java defined by the Java Grande Forum
The current release contains:
The core library
The runtime infrastructure
The test-suite
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3. MPJ Express Configurations
MPJ Express can be configured in two ways:
Multicore Configuration: This configuration is used by developers who want to execute their parallel Java applications on multicore or shared memory machines (laptops and desktops).
Cluster Configuration: This configuration is used by developers who want to execute their parallel Java applications on distributed memory platforms including clusters and network of computers.
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4. Multicore Configuration
The users can use multicore device driver (also known as shared memory device driver) in the multicore configuration
Main Memory
CPU 0
CPU 1
CPU 2
CPU 3
Proc 0
Proc 1
Proc 2
Proc 3
Fig1: MPJ Express executing in the multicore configuration with four threads on a quad core processor
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5. Advantages of Multicore Configuration
Incremental Development:
Users can first develop parallel applications on desktops/laptops using multicore configuration and then take the same code to distributed memory platforms including clusters
Teaching Purposes:
This configuration is preferred for teaching purposes since students can execute message passing code on their personal computers
Debugging and Profiling:
IDEs like Eclipse can be used for easier debugging and profiling
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6. Cluster Configuration
Application developers can opt to use either of the two communication drivers in the cluster configuration
Java NIO Device Driver (niodev) It can be used to execute MPJ Express programs on Ethernet-based interconnects.
Myrinet Device Driver (mxdev): Many clusters today are equipped with high performance low latency networks like Myrinet.
Lets consider a cluster comprising of 8 compute nodes.
Every process is started on different node while running code with Cluster Configuration, depending upon the machines file 1 2 3 4 5 6 7
Fig2: MPJ Express executing in the cluster
configuration with 8 processes on a
cluster with 8 compute nodes
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7. MPJ Express Installation (UNIX/Linux/Mac)
Pre-requisites
Java 1.5 (stable) or higher
Apache ant or higher (Optional)
Perl (Optional)
Running MPJ Express Programs in the Multicore Configuration
Download MPJ Express and unpack it.
Set MPJ_HOME and PATH environmental variables:
export MPJ_HOME=/path/to/mpj/
export PATH=$PATH:$MPJ_HOME/bin
(These above two lines can be added to ~/.bashrc)
Write your MPJ Express program (HelloWorld.java) and save it.
Compile: javac -cp.:$MPJ_HOME/lib/mpj.jar HelloWorld.java
Execute: mpjrun.sh -np 4 HelloWorld.java
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8. MPJ Express Installation (UNIX/Linux/Mac) Cont’d
Running MPJ Express Programs in the Cluster Configuration
Download MPJ Express and unpack it.
Set MPJ_HOME and PATH environmental variables:
export MPJ_HOME=/path/to/mpj/
export PATH=$PATH:$MPJ_HOME/bin
(These above two lines can be added to ~/.bashrc)
Write a machines file (name it “machines”) stating hostnames or IP addresses of all the machines involved in the parallel execution
Write your MPJ Express program (HelloWorld.java) and save it.
Start Daemons: mpjboot machines
Compile: javac -cp.:$MPJ_HOME/lib/mpj.jar HelloWorld.java
Execute: mpjrun.sh -np 4 HelloWorld.java
Stop daemons: mpjhalt machines
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9. MPJ Express Installation (Windows)
Pre-requisites
Java 1.5 (stable) or higher
Apache ant or higher (Optional)
Perl (Optional)
Running MPJ Express Programs in the Multicore Configuration
1. Download MPJ Express and unpack it.
2. Set MPJ_HOME and PATH environmental variables. Right-click My Computer->Properties->Advanced tab->Environment Variables and export the following system variables (User variables are not enough)
Set the value of MPJ_HOME = c:\mpj (assuming mpj is in c:\
Append the c:\mpj\bin directory to the PATH variable
Cygwin on Windows: (assuming mpj is 'c:\mpj‘): The recommended way to is to set variables as in Windows. If you want to set variables in cygwin shell
export MPJ_HOME="c:\\mpj“
export PATH=$PATH:"$MPJ_HOME\\bin"
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10. MPJ Express Installation (Windows) Cont’d
Write your MPJ Express program (HelloWorld.java) and save it.
Compile: javac -cp.:$MPJ_HOME/lib/mpj.jar HelloWorld.java
Execute: mpjrun.bat -np 4 HelloWorld.java
For running MPJ Express programs in the cluster configuration, refer to the $MPJ_HOME/README-win.txt and $MPJ_HOME/doc/windowsguide.pdf
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11. Writing Programs with MPJ Express
A sample Program with MPJ Express is
Save this Program as HelloWorld.java
import mpi.*;
public class HelloWorld {
public static void main(String args[]) throws Exception {
MPI.Init(args);
int me = MPI.COMM_WORLD.Rank();
int size = MPI.COMM_WORLD.Size();
System.out.println("Hi from <"+me+">");
MPI.Finalize(); }
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12. Executing MPJ Express Programs
Compiling
UNIX/Linux/Mac: javac –cp .:$MPJ_HOME/lib/mpj.jar HelloWorld.java
Windows: javac –cp .:%MPJ_HOME%/lib/mpj.jar HelloWorld.java
Running with Multicore Configuration
UNIX/Linux/Mac: mpjrun.sh –np <no. of processors> HelloWorld.java
Windows: mpjrun.bat –np <no. of processors> HelloWorld.java
Running with Cluster Configuration
Start the daemons
UNIX/Linux/Mac: mpjrun.sh –np <no. of processors> -dev niodev HelloWorld
Windows: mpjrun.bat –np <no. of processors> -dev niodev HelloWorld
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13. Executing Programs with MPJ Express on UNIX/Linux/Mac
Multicore Configuration
Cluster Configuration
Add Snapshots ….
First show snapshots for multicore:
1. Logged onto my laptop, which has for example (a quad-core)
2. Execute …
3. and Explain with previous figure how processes are running …
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14. Executing Programs with MPJ Express on Windows
Multicore Configuration
Cluster Configuration
Add Snapshots ….
First show snapshots for multicore:
1. Logged onto my laptop, which has for example (a quad-core)
2. Execute …
3. and Explain with previous figure how processes are running …
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15. Additional Runtime Arguments
The mpjrun.[sh/bat] script accepts some additional arguments which can be passed according to the user preferences. Some of them are
np switch: If a value is specified, then MPJ Express starts those many processes for the user application. It can be specified like mpjrun.[sh/bat] –np 2 ProgramName.
dev switch: This switch can be given at runtime to change to the appropriate device driver. It can be used as mpjrun.[sh/bat] –dev multicore/niodev/mxdev ProgramName.
machinesfile switch: While running programs, MPJ Express runtime expects a file with name “machines” in the current directory. User can also specify a machines file with different name using machinesfile switch as mpjrun.[sh/bat] machinesfile myFile ProgramName
wdir switch: If your programs reads some file, then it may be a good idea to separate this file from your application classes, or copy it to a tmp directory and specify this tmp directory as working directory using -wdir switch.
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16. Manuals and Help Resources
Windows
Linux
README (Quick Start Guide)
$MPJ_HOME/README-win.txt
$MPJ_HOME/README
User Guide
$MPJ_HOME/doc/windowsguide.pdf
$MPJ_HOME/doc/linuxguide.pdf
Visit MPJ Express ( for more details.
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17. Contact and Support
MPJ Express Users Mailing List (
Alternatively, the users can contact us directly by .
Aamir Shafi
Bryan Carpenter
Mark Baker
4/15/2017

18. Contributors Aamir Shafi Jawad Manzoor Kamran Hamid Mohsan Jameel
Bryan Carpenter
Mark Baker
Hong Ong
Guillermo Taboada
Sabela Ramos
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19. Acknowledgements
The project partners received a generous grant from the British Council under the PMI2 Connect program (
Project Title: CollAborative Multicore Programming Using Scientific Java Messaging
Project Start Date: September 2008
Duration: 2 Years
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