public class Runner {
    private static String s;

    public static void main(String[] args) throws Exception {
        new Thread(new Runnable() {
            @Override public void run() {
                while (s == null) {
                    // No-op.
                }

                System.out.println("2: String change observed: " + s);
            }
        }).start();

        Thread.sleep(1000);

        s = "str";

        System.out.println("1: String changed.");
    }
}

import sun.misc.*;

import java.lang.reflect.*;
import java.security.*;

public class Runner {
    private static int s;

    private static int s0;

    private static int control;

    private static final Unsafe UNSAFE;

    private static final Object BASE;
    private static final long OFFSET;

    static {
        UNSAFE = unsafe();

        try {
            BASE = UNSAFE.staticFieldBase(Runner.class.getDeclaredField("s"));
            OFFSET = UNSAFE.staticFieldOffset(Runner.class.getDeclaredField("s"));
        }
        catch (Exception e) {
            throw new RuntimeException(e);
        }
    }

    public static void main(String[] args) throws Exception {
        new Thread(new Runnable() {
            @Override public void run() {
                while (s == 0) {
                    s0 = UNSAFE.getInt(BASE, OFFSET);

                    control++;
                }

                System.out.println("2: change observed: " + s);
            }
        }).start();

        Thread.sleep(1000);

        s = 1;

        System.out.println("1: changed.");

        while (true) {
            Thread.sleep(1000);

            System.out.println("1: What 2 saw through Unsafe: " + s0);
            System.out.println("1: Control: " + control);
        }
    }

    public static Unsafe unsafe() {
        try {
            return Unsafe.getUnsafe();
        } catch (SecurityException ignored) {
            try {
                return AccessController.doPrivileged
                    (new PrivilegedExceptionAction<Unsafe>() {
                        @Override
                        public Unsafe run() throws Exception {
                            Field f = Unsafe.class.getDeclaredField("theUnsafe");
                            f.setAccessible(true);
                            return (Unsafe) f.get(null);
                        }
                    });
            } catch (PrivilegedActionException e) {
                throw new RuntimeException("Cannot get Unsafe.");
            }
        }
    }
}