Transcript 1. Intriduction to Java Programming for Beginners, Novices

Parallel Programming
Dr Andy Evans
Parallel programming
Various options, but a popular one is the Message Passing
Interface (MPI). This is a standard for talking between nodes
implemented in a variety of languages.
With shared memory systems, we could just write to that, but
enacting events around continually checking memory isn’t very
efficient. Message passing better.
API description formulated by the Java Grande forum.
A good implementation is MPJ Express:
http://mpj-express.org
Language implementation and runtime/manager.
Other implementations
mpiJava:
http://www.hpjava.org/mpiJava.html
P2P-MPI:
http://grid.u-strasbg.fr/p2pmpi/
(well set up for Peer-to-Peer development)
Some (like mpiJava) require an underlying C implementation to
wrap around, like LAM:
http://www.lam-mpi.org
MPJ Express
Allows you to use their MPI library to run MPI code.
Sorts out communication as well:
Runs in Multicore Configuration: i.e. on one PC.
Runs each process as a thread, and distributes them around
available cores.
Great for developing/testing.
Also in Cluster Configuration: i.e. on multiple PCs.
How to check processor/core numbers
My Computer → Properties
Right-click taskbar → Start
Task Manager (→ Resource
Monitor in Win 8)
With Java:
Runtime.getRuntime().availableProcessors();
General outline
You write the same code for all nodes.
However, the behaviour changes depending on the node
number.
You can also open sockets to other nodes and send them stuff if
they are listening.
if (node == 0) {
listen();
} else {
sendData();
}
Usually the MPI environment will organise running the code on
the other nodes if you tell it to run the code and how many
nodes you want.
MPI basics
API definition for communicating between Nodes.
MPI.Init(args)
Call the initiation code
MPI.Finalize()
with a String[] / Shut down.
MPI.COMM_WORLD.Size()
Get the number of
available nodes.
MPI.COMM_WORLD.Rank()
Get the node the code is
running on
Usually within try-catch:
} catch (MPIException mpiE) {
mpiE.printStackTrace();
}
Load balancing
This kind of thing is common:
int nodeNumberOfAgents = 0;
if (node != 0) {
nodeNumberOfAgents = numberOfAgents /(numberOfNodes - 1);
if (node == (numberOfNodes – 1)) {
nodeNumberOfAgents = nodeNumberOfAgents +
(numberOfAgents % (numberOfNodes - 1));
}
agents = new Agent[nodeNumberOfAgents];
for (int i = 0; i < nodeNumberOfAgents; i++) {
agents[i] = new Agent();
}
}
Sending stuff
MPI.COMM_WORLD.Send
(java.lang.Object,startIndex,lengthToSend,
dataType,nodeToSendTo,messageIntId);
All sent objects must be 1D arrays, even if only one thing in
them.
dataType:
Array of booleans: MPI.BOOLEAN
Array of doubles: MPI.DOUBLE
Array of ints:
MPI.INT
Array of nulls:
MPI.NULL
Array of objects:
MPI.OBJECT
Objects must implement java.io.Serializable
Receiving stuff
MPI.COMM_WORLD.Recv
(java.lang.Object,startIndex,lengthToGet,
dataType,nodeSending,messageIntId);
Object is a 1D array that gets the data put into it.
Might, for example, be in a loop that increments nodeSending,
to recv from all nodes.
Other MPI commands
Any implementation of the API should have the same methods
etc.
For MPJ Express, see:
http://mpj-express.org/docs/javadocs/index.html