Question

Im working on a java application that involves threads. So i just wrote a piece of code to just familiarize myself with the execution of multiple yet concurrent threads

public class thready implements Runnable{
private int num;

public thready(int a) {
    this.num=a;
}
public void run() {
  System.out.println("This is thread num"+num);
  for (int i=num;i<100;i++)
  {
      System.out.println(i);
  }
}
public static void main(String [] args)
{
    Runnable runnable =new thready(1);
    Runnable run= new thready(2);
    Thread t1=new Thread(runnable);
    Thread t2=new Thread(run);
    t1.start();
    t2.start();
}}

Now from the output of this code, I think at any point in time only 1 thread is executing and the execution seems to alternate between the threads. Now i would like to know if my understanding of the situation is correct. And if it is I would like to know if there is any way in which i could get both threads to executing simultaneously as i wish to incorporate this scenario in a situation wherein i want to write a tcp/ip socket listener that simultaneously listens on 2 ports, at the same time. And such a scenario cant have any downtime.
Any suggestions/advice would be of great help.

Cheers

Answer 1

How many processors does your machine have? If you have multiple cores, then both threads should be running at the same time. However, console output may well be buffered and will require locking internally – that’s likely to be the effect you’re seeing.

The easiest way to test this is to make the threads do some real work, and time them. First run the two tasks sequentially, then run them in parallel on two different threads. If the two tasks don’t interact with each other at all (including “hidden” interactions like the console) then you should see a roughly 2x performance improvement using two threads – if you have two cores or more.

As Thilo said though, this may well not be relevant for your real scenario anyway. Even a single-threaded system can still listen on two sockets, although it’s easier to have one thread responsible for each socket. In most situations where you’re listening on sockets, you’ll spend a lot of the time waiting for more data anyway – in which case it doesn’t matter whether you’ve got more than one core or not.

EDIT: As you’re running on a machine with a single core (and assuming no hyperthreading) you will only get one thread executing at a time, pretty much by definition. The scheduler will make sure that both threads get CPU time, but they’ll basically have to take turns.