Tuesday May 13, 2008

Controlling Threads with concurrent package

For long, I have been using Runnable interface to get the long running non interactive natured stuff done in the background. In some previous posts, I had mentioned the crude way of using ThreadGroup to achieve pooling sort of control. It was also fun working on a task scheduler that ran tasks in controlled set of threads. Logically, what do you need ? The pool size, the Runnable targets, an infinite loop and a data structure to control the thread scheduling !! So the code looked really.. as we call in India.. 'Fundooo' ! But when I look at the Concurrent package, the same code looks like a floppy disk in front of a DVD. I haven't explored the package completely so don't want to say a blue ray disk.

Just for my understanding, let me post a test program that I can anytime compile and run later to refresh my memory.

import java.util.concurrent.*;
import java.util.Random;

public class TestConcurrent {
        public static void main(String args[]) {
                ExecutorService runner = Executors.newSingleThreadExecutor();
                ExecutorService pool = Executors.newFixedThreadPool(5);

                int style = 1;

                try { style = (new Integer(args[0])).intValue();
                } catch (Exception e ) {}

              switch(style) {

              case 1:
                  System.out.println("Running in separate threads...");
                  for(int oldstyle=0; oldstyle<10; oldstyle++) {
                      new Thread(new TestRunnable()).start();
                  }
                  break;

              case 2:
                  System.out.println("Running in a worker thread....");
                  for(int newstyle=0; newstyle<10; newstyle++) {
                      runner.submit(new TestRunnable());
                  }
                  runner.shutdown();
                  break;

              case 3:
                  System.out.println("Running in a thread pool....");
                  for(int newstyle=0; newstyle<10; newstyle++) {
                      pool.submit(new TestRunnable());
                  }
                  pool.shutdown();
                  break;
              }

              System.out.println("Main is over....");
        }
}

class TestRunnable implements Runnable {

    private static int i = 0;
    private int member = 0;
    private int runtime = 0;

    public TestRunnable() {
       member = ++i;
       runtime = (new Random()).nextInt(10);
    }

    public void run() {
        System.out.println("I am instance " + member + " with runtime " + runtime + " seconds");
        try { Thread.sleep(runtime * 1000); }catch(Exception e) {System.out.println("Interrupted");}
        System.out.println("Instance "+ member + " runtime over...!");
    }

}