Lock Mechanism Doubt

[Lee Mark]

class MyRunnable implements Runnable {

    Integer i = 1;

    
    }
    

    public    void run() {
 
        synchronized (i) {
            for (int i = 0; i < 100; i++) {
                try {
                    Thread.sleep(0);
                     System.out.print(Thread.currentThread().getName() );
                } catch (InterruptedException ex) {
                    Logger.getLogger(MyRunnable.class.getName()).log(Level.SEVERE, null, ex);
                }
                
            }
            

        }
       // System.out.println(Thread.currentThread().getName() + " : i am out of run");
    }
}

public class StaticSync {

    public static void main(String[] args) throws InterruptedException {
        MyRunnable mr = new MyRunnable();
        Thread t1 = new Thread(mr, "a");
      
        Thread t2 = new Thread(mr, "b");


        Thread t3 = new Thread(mr, "c");
        t1.start();
        t2.start();
        t3.start();

        t1.join();
        t2.join();
        t3.join();


  //      System.out.println("" + mr.getSb());
    }
}

please explain the behaviour of this code..

[Rok Štelcer]

Hi,

I'm not sure what do you want from us to explain, so I've added a few comments.

Lee Mark wrote:please explain the behaviour of this code.

class MyRunnable implements Runnable {

    Integer i = 1;

    
    } // I guess this one is a typo
    

    public    void run() {
 
        synchronized (i) {   // guaranties that this code block will be executed by a single thread at the time.
            for (int i = 0; i < 100; i++) {
                try {
                    Thread.sleep(0); // nothing
                     System.out.print(Thread.currentThread().getName() );
                } catch (InterruptedException ex) {
                    Logger.getLogger(MyRunnable.class.getName()).log(Level.SEVERE, null, ex);
                }
                
            }
            

        }
       // System.out.println(Thread.currentThread().getName() + " : i am out of run");
    }
}

public class StaticSync {

    public static void main(String[] args) throws InterruptedException {
        MyRunnable mr = new MyRunnable(); // creating our custom runnable
        Thread t1 = new Thread(mr, "a"); // thread creation
      
        Thread t2 = new Thread(mr, "b");


        Thread t3 = new Thread(mr, "c");
        t1.start(); // start a t1 
        t2.start(); // start a t2
        t3.start(); // start a t3

        t1.join(); //current thread (main) should wait for t1 to finished
        t2.join(); //current thread (main) should wait for t2 to finished
        t3.join(); //current thread (main) should wait for t3 to finished


  //      System.out.println("" + mr.getSb());
    }
}

Hope this helps.

Regards,
Rok

[Lee Mark]

but what if i create i new for every thread befor thay start i am getting same output i tried it running atleast 15 itimes to ensure tht..


i am adding

mr.i = new Integer(2);

before each thread start call..
comment again

[Rok Štelcer]

Hi,

Lee Mark wrote:but what if i create i new for every thread befor thay start i am getting same output i tried it running atleast 15 itimes to ensure tht..


i am adding

mr.i = new Integer(2);

before each thread start call..
comment again

If I understood you correctly, you've suggested following:

...
        Thread t1 = new Thread(mr, "a");
        Thread t2 = new Thread(mr, "b");
        Thread t3 = new Thread(mr, "c");

        mr.i = new Integer(1); // number doesn't matter ... it is always a new object
        t1.start();
        mr.i = new Integer(2);
        t2.start();
        mr.i = new Integer(3); 
        t3.start();
...

You have to understand that threads are not really executed in parallel, however in a sequence (handled by OS).
When you call start() on a thread, this just means that the thread is ready to run, however whether it will be started or not is up to the scheduler.
So, the scheduler determines which thread will be started at what time...
Therefore the result could/would be the same as without above changes, because all running threads will have to gain the lock on e.g. Integer(3).

Hope I answered your question.


Regards,
Rok