Why my boolean variable should be volatile while stopping thread loop? [duplicate]

Question

Let's say I have a thread including while loop and I want to stop it "from outside".

public class MyThread extends Thread {

    private boolean running = true;

    @Override
    public void run() {
        while (running) {
            // do something
        }
    }

    public void setRunning(boolean running) {
        this.running = running;
   }
}

And here is the Main class:

public class Main {
    public static void main(String[] args) {
        MyThread mt = new MyThread();
        mt.start();
        // do something
        mt.setRunning(false);
    }
}

It seems to be stopping properly, but I have read that the boolean should be also volatile. Why? Will it quicken the stopping?

Answer 1

When Concurrent thread will cache running variable that means it will cache in thread working memory.

The volatile keyword in Java is used as an indicator to Java compiler and Thread that do not cache value of this variable and always read it from main memory. So if you want to share any variable in which read and write operation is atomic by implementation you have to declare as volatile variable.

you can have good idea in you look into the below picture