让我了解此线程同步失败

Question

I'll cut it short.

Given this code:

public class Test {

private static long counter = 1000000;

public static void main(String[] args) {

    T t = new T();

    t.start();

    while(counter >= 0){
        counter--;
        System.out.println(counter);
    }
    System.out.println(t.isAlive());    

}

private static class T extends Thread{

    @Override
    public void run() {

        while(counter > 0);

        System.out.println("end reached");



     }

   }    
 }

Why in the name of the gods doesn't T print "end Reached"? Counter goes down to -1 and t is alive. If I decrease the counter it sometimes work.

Answer 1

you need to make counter volatile . Thread T is using a local copy.