Question about Yield

[Anonymous]

Hello All,

I was trying something on yield() method , and found that behavior of the program is not what I expected. I'm sure, I must have mistaken the concept of yield, and now would like to know the science behind this.

    
public class MyClass implements Runnable{
private static int value=10;
public void run(){
System.out.println(this);
synchronized(this){
System.out.println(Thread.currentThread().getName());
++value;
Thread.yield();
System.out.println(value);
}
}
public static void display(){
System.out.println(value);
}
public static void main(String[] args) throws InterruptedException{
MyClass m=new MyClass();
Thread t1=new Thread(m);
Thread t2=new Thread(m);
t1.start();
t2.start();
Thread.sleep(3000);
display();
}
}
 

As per K&B in page 712 on threads, it says yield() method would keep the locks and would not release them.

From the above statement, I assumed that, when the first thread enters run, and have a lock on this (MyClass) object, it increments value and would keep the lock with itself without releasing it (due to yield() method). This should prevent the second thread ,entering run and have a lock on this (as already being held with first thread). So I believed that value would be incremented only once and the value would be printed 11 some time later after Main thread is awaken. But this is not what happening . Value is incremented twice and 12 is printed finally in main method.

Where did I do a mistake in understanding this concept? Please some one clarify me on this.Thanks in advance.

[Henry Wong]

Where did I do a mistake in understanding this concept? Please some one clarify me on this.Thanks in advance.

Well, assuming the yield() was even honored, what do you think will happen to the thread? Yield just means to give up the current timeslice. The other thread will block because it can't get the lock, and the main thread is sleeping, which thread do you think will run again?

Henry

[Anonymous]

Oh I got it now . I thought, it was the second thread that is entering into the Run. I never realized that the first thread can again take over the control. That was so stupid of me .


Thanks Henry, for making me understand the logic behind that