Would someone tell me something about multithread and multiprocessor

Question

Hey, would you be so kind to tell me something about how to progrmme with using multithread in multiprocessro? and where can I find something about it? My problem is that
Assume that you have to write a computer program that will receive as input a single array
storing a large number of integers. The program has to compute the prefix sums of the
number sequence.
Given a sequence of numbers x1, x2, ..., xn, the prefix sums are the partial sums:
s1 = x1
s2 = x1 + x2
sn = x1 + x2 + ... + xn
�You have to be prepared to write a program for program should be able to use a variable, user-specified, number of processors. For
example, the user should be able to run the program using any number of processors P
between 1 and 16. The number of processors P can either be selected using a command
line argument or the program can prompt the user.
�Your program should be able to sum a variable, user-specified, number of integers. The
integers in the input sequence should be randomly generated inside your program. (That
is, the user will input n, and the program will then randomly generate n numbers.)
�Your program should print out (either to the standard output or to a file) in ascending
order the prefix sums computed: s1, s2, �, sn.
Can someone give me some help? I have no idea about how to do it?
thanks a lot of

Answer 1

I think perhaps you are asking about how to create threads in Java? I'm not sure, but I'll give you some background anyway. Basically all that you need to know is documented in the class java.lang.Thread. If you want a class to run on a separate thread then you can do one of two things:
(a) define a class that extends Thread.
(b) define a class that implements Runnable.
I prefer the latter, but it's up to you. So, for example, if I have some computationally expensive algorithm to execute I would define a class like this:
public class ImExpensive implements Runnable {
����public void run() {
��������<insert code here>
����}
Then when you want to run the algorithm you do this:
����ImExpensive o = new ImExpensive();
����new Thread(o).start();
The second line in this case constructs a thread that the object 'o' can run on (the start() method causes the run() method in the ImExpensive class to execute).
Now, as for running on multi-processors, I have never done this so I am not too sure. But all that you have to do is figure out a way of associating the thread that was created with a particular processor.
Also, be careful when using threads. Everything will be OK if your computations are mutually exclusive (ie: they aren't interdependent). If they aren't then you might run into what is sometimes called "the racehorse problem". This is a phenomenon that occurs because you can't guarantee which threads are going to finish first or indeed the order of interleaved operations. It's difficult to describe but this tutorial may help you out.
http://java.sun.com/docs/books/tutorial/essential/threads/
Hope that helps. :)
Ben