Question

Java Programming Language
Write code in Java that shows race condition using two or more threads.
Give comments on first line (can be multiple lines), explain race condition that occurs in your program.

Answer 1

Solution:

Race condition:

Race condition in Java occurs in a multi-threaded environment when more than one thread try to access a shared resource (modify, write) at the same time. Since multiple threads try to race each other to finish executing a method thus the name race condition.

Code in Java that shows race condition using two or more threads:

class Counter  implements Runnable{
    private int c = 0;

    public void increment() {
        try {
            Thread.sleep(10);
        } catch (InterruptedException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        c++;
    }

    public void decrement() {    
        c--;
    }

    public int getValue() {
        return c;
    }
    // race condition that occurs in program and see how the shared variable c is giving wrong values

    @Override
    public void run() {
        //incrementing
        this.increment();
        System.out.println("Value for Thread After increment " 
        + Thread.currentThread().getName() + " " + this.getValue());
        //decrementing
        this.decrement();
        System.out.println("Value for Thread at last " 
        + Thread.currentThread().getName() + " " + this.getValue());        
    }
}

public class RaceConditionDemo{
    public static void main(String[] args) {
        Counter counter = new Counter();
        Thread t1 = new Thread(counter, "Thread-1");
        Thread t2 = new Thread(counter, "Thread-2");
        Thread t3 = new Thread(counter, "Thread-3");
        t1.start();
        t2.start();
        t3.start();
    }    
}

Output:

Value for Thread After increment Thread-2 3
Value for Thread at last Thread-2 2
Value for Thread After increment Thread-1 2
Value for Thread at last Thread-1 1
Value for Thread After increment Thread-3 1
Value for Thread at last Thread-3 0

It can be seen how the shared variable c is giving wrong values.

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