Threads with separate lock Problem

[Mohit G Gupta]

    class XSync implements Runnable{
     

public void run(){
          synchronized("s"){
               System.out.print("X "+Thread.currentThread().getName());
               this.run2();
          }
     }
     public void run2(){
          synchronized("s"){
               System.out.print("X2 ");
          }
     }
}

public class MCe{
     public static void main(String args[]){
          XSync ns=new XSync();
          XSync ns1=new XSync();
          Thread t1=new Thread(ns);
          Thread t2=new Thread(ns1);
          t1.start();
          t2.start();
     }
}

can' the output
X X X2 X2
possible
both threads have there separate locks

[Arjun Srivastava]

mohitkumar gupta wrote:
both threads have there separate locks

under synchronization block,we acquire lock on object reference not on thread.

[Mohit G Gupta]

Under synchronization block,we acquire lock on object reference not on thread.

Thread t1 has lock on ns
and Thread t2 has lock on ns2

[Abimaran Kugathasan]

Try this!

    class XSync implements Runnable{


public void run(){
          synchronized("s"){
               System.out.print("X "+Thread.currentThread().getName() + " ");
               this.run2();
          }
     }
     public void run2(){
          synchronized("s"){
               System.out.println("X2 ");
          }
     }
}

public class MCe{
     public static void main(String args[]){
          XSync ns=new XSync();
          XSync ns1=new XSync();
          Thread t1=new Thread(ns);
          Thread t2=new Thread(ns1);
          t1.start();
          t2.start();
     }
}

You are synchronized with a single object. So, output can be predicted. There are two possiblr outputs. Could you able to fine those?

[Abimaran Kugathasan]

mohitkumar gupta wrote:

Thread t1 has lock on ns
and Thread t2 has lock on ns2

No!

[Arjun Srivastava]

mohitkumar gupta wrote:
Thread t1 has lock on ns
and Thread t2 has lock on ns2

you assumption according to your knowledge is wrong.
i don't know if you have read the book carefully or not.
Thread always hold the lock on the object,every object has built in lock that comes in action when the object has synchronized method code or block.
does your code compiles fine?

[Mohit G Gupta]

    class XSync implements Runnable{
     

public void run(){
          synchronized(this){                        //modified
               System.out.print("X "+Thread.currentThread().getName());
               this.run2();
          }
     }
     public void run2(){
          synchronized(this){                     //modified
               System.out.print("X2 ");
          }
     }
}

public class MCe{
     public static void main(String args[]){
          XSync ns=new XSync();
          XSync ns1=new XSync();
          Thread t1=new Thread(ns);
          Thread t2=new Thread(ns1);
          t1.start();
          t2.start();
     }
}

Sorry, i had put the wrong code

Thread t1 would have lock on ns
Thread t2 would have lock on ns1
Now, IS the output:
X X X2 X2
possible now ?

[Abimaran Kugathasan]

mohitkumar gupta wrote:
Thread t1 has lock on ns
and Thread t2 has lock on ns2

OK, let's clear it. When a thread enters the to execute a method or block with is synchronized on an object, then the thread acquire the lock of that particular object. In the above code, you've synchronized String Literal Pool object "s", in your run() method. So, thread acquire the lock of the String Literal Pool object.

[Mohit G Gupta]

Arjun Srivastava:
i don't know if you have read the book carefully or not.
Thread always hold the lock on the object,every object has built in lock that comes in action when the object has synchronized method code or block.

so,Thread t1 or t2 whosoever runs first would automatically acquire lock on XSync object when,it see's synchronize(this).then,that thread would not release lock until the code in synchronized block or function is complete


Am,i right now ?

[Abimaran Kugathasan]

mohitkumar gupta wrote:

    class XSync implements Runnable{
     

public void run(){
          synchronized(this){                        //modified
               System.out.print("X "+Thread.currentThread().getName());
               this.run2();
          }
     }
     public void run2(){
          synchronized(this){                     //modified
               System.out.print("X2 ");
          }
     }
}

public class MCe{
     public static void main(String args[]){
          XSync ns=new XSync();
          XSync ns1=new XSync();
          Thread t1=new Thread(ns);
          Thread t2=new Thread(ns1);
          t1.start();
          t2.start();
     }
}

Sorry, i had put the wrong code

Thread t1 would have lock on ns
Thread t2 would have lock on ns1
Now, IS the output:
X X X2 X2
possible now ?

Now, your asumption is OK, But what is the logic of synchronizing here? Now, 4 possible outputs! I think!

[Abimaran Kugathasan]

mohitkumar gupta wrote:
acquire lock on XSync object when,it see's synchronize(this).then,
Am,i right now ?

This isn't an object, it's a class!

[Arjun Srivastava]

your code doesn't compiles on my machine,may be problem with my JDK1.6,which i have installed a fresh copy
try this code given below.

class XSync extends Thread{
public void run(){
          synchronized(this){                        //modified
               System.out.print("X "+Thread.currentThread().getName());
               this.run2();
          }
     }
     public void run2(){
          synchronized(this){                     //modified
               System.out.print("X2 ");
          }
     }
}
public class Main{
     public static void main(String args[]){
          XSync t1=new XSync();
          XSync t2=new XSync();
         t1.start();
          t2.start();
     }
}

mohitkumar gupta wrote:
so,Thread t1 or t2 whosoever runs first would automatically acquire lock on XSync object when,it see's synchronize(this).then,that thread would not release lock until the code in synchronized block or function is complete
Am,i right now ?

yes,XXX2X2 can be possible,try it.
see that you have two different thread references which are invoking two different methods,no use of synchronization here.

[Mohit G Gupta]

Abimaran :
acquire lock on XSync object when,it see's synchronize(this).then,
Am,i right now ?

i mean to say XSync's object

[Abimaran Kugathasan]

OK, So, you've cleared it?

[Mohit G Gupta]

so,i think Arjun Srivastava that the both the code below are doing the same thing

       class XSync implements Runnable{
     

public void run(){
          synchronized(this){                        //modified
               System.out.print("X "+Thread.currentThread().getName());
               this.run2();
          }
     }
     public void run2(){
          synchronized(this){                     //modified
               System.out.print("X2 ");
          }
     }
}

public class MCe{
     public static void main(String args[]){
          XSync ns=new XSync();
          XSync ns1=new XSync();
          Thread t1=new Thread(ns);
          Thread t2=new Thread(ns1);
          t1.start();
          t2.start();
     }
}


 

  class XSync extends Thread{
public void run(){
          synchronized(this){                        //modified
               System.out.print("X "+Thread.currentThread().getName());
               this.run2();
          }
     }
     public void run2(){
          synchronized(this){                     //modified
               System.out.print("X2 ");
          }
     }
}
public class Main{
     public static void main(String args[]){
          XSync t1=new XSync();
          XSync t2=new XSync();
         t1.start();
          t2.start();
     }
}  

[Abimaran Kugathasan]

Yes, In the Thread's run() method,

public void run() {
           if (target != null) {
               target.run();
           }
}

So, in your case, both will give same output!