Enthuware

It may print any number between -5000 to 5000.

Making variable counter volatile only ensures that if it is updated by one thread, another thread will see the updated value. However, it still does not ensure that the increment and decrement operations will be done atomically. Thus, it is possible that while one thread is performing counter++, another thread corrupts the value by doing counter--. Because of this corruption, it is not possible to determine the final value of counter.

 
public class RunTest {    
 
public static volatile int counter = 0;     
static class RunnerDec implements Runnable{ 
        
public void run(){             
for(int i=0;i<5000; i++){
                 counter--;             }
         }
     } 
     static class RunnerInc implements Runnable{
         public void run(){
             for(int i=0;i<5000; i++){
                 counter++;             }
         }
     } 
         public static void main(String[] args) {
         RunnerDec rd = new RunnerDec();
         RunnerInc ri = new RunnerInc();
         Thread t1 = new Thread(rd); 
        Thread t2 = new Thread(ri);
         t1.start();
         t2.start(); 
        try{
             t1.join();
             t2.join();
         }catch(Exception e){ 
            e.printStackTrace();
         }
         System.out.println(counter); 
    }
      }

admin wrote:This is an important topic and if you are unable to understand the explanation then you need to go through a good book to first understand what is race condition and how it happens in Java. Then you will understand this question very easily.
You might want to start here: http://stackoverflow.com/questions/3451 ... -condition
HTH,
Paul.

shareef.hiasat wrote:

admin wrote:This is an important topic and if you are unable to understand the explanation then you need to go through a good book to first understand what is race condition and how it happens in Java. Then you will understand this question very easily.
You might want to start here: http://stackoverflow.com/questions/3451 ... -condition
HTH,
Paul.

Thanks for replying , am aware of data race problem but this case confuses me , i mean
if the variable counter is static shouldnt

t1.join(); means the for of increment 5000 times is complete true or false
and
t2.join(); means the for of decrement of 5000 times is complete