1. package thread;
   
2. 
   
3. import java.lang.reflect.Field;
   
4. import sun.misc.Unsafe;
   
5. public class Test {
   
6.   
   
7.          public static void main(String[] args) throws Exception {
   
8.          System.out.println(A.flag);
   
9.          new A();
   
10.          new A();
    
11.          System.out.println(A.flag);
    
12.         }
    
13.     }
    
14. class A
    
15. {
    
16. public static final boolean flag=false;
    
17. public A() throws Exception
    
18. {
    
19. if(getflag()) throw new Exception();       
    
20. getUnsafe().putBooleanVolatile(A.class, getUnsafe().staticFieldOffset(A.class.getField("flag")), true);
    
21. }
    
22. private static final Unsafe getUnsafe()  
    
23. {
    
24. Unsafe unsafe=null;
    
25. try{
    
26. Field field= Unsafe.class.getDeclaredField("theUnsafe");
    
27. field.setAccessible(true);
    
28.   unsafe=(Unsafe)field.get(Unsafe.class);
    
29.    }
    
30. catch(Exception e){}
    
31. return unsafe;
    
32. }
    
33. private static final boolean getflag()
    
34. {
    
35. boolean b = false;
    
36.         try{
    
37.        long start= getUnsafe().staticFieldOffset(A.class.getField("flag"));
    
38.        b=getUnsafe().getBooleanVolatile(A.class, start);}
    
39.         catch(Exception e){}
    
40. return b;
    
41. }
    
42. }

复制代码

1. package thread;
   
2. 
   
3. import java.lang.reflect.Field;
   
4. import sun.misc.Unsafe;
   
5. public class Test {
   
6.   
   
7.          public static void main(String[] args) throws Exception {
   
8.          System.out.println(A.flag);
   
9.          new A();
   
10.          new A();
    
11.          System.out.println(A.flag);
    
12.         }
    
13.     }
    
14. class A
    
15. {
    
16. public static final boolean flag=false;
    
17. public A() throws Exception
    
18. {
    
19. if(getflag()) throw new Exception();       
    
20. getUnsafe().putBooleanVolatile(A.class, getUnsafe().staticFieldOffset(A.class.getField("flag")), true);
    
21. }
    
22. private static final Unsafe getUnsafe()  
    
23. {
    
24. Unsafe unsafe=null;
    
25. try{
    
26. Field field= Unsafe.class.getDeclaredField("theUnsafe");
    
27. field.setAccessible(true);
    
28.   unsafe=(Unsafe)field.get(Unsafe.class);
    
29.    }
    
30. catch(Exception e){}
    
31. return unsafe;
    
32. }
    
33. private static final boolean getflag()
    
34. {
    
35. boolean b = false;
    
36.         try{
    
37.        long start= getUnsafe().staticFieldOffset(A.class.getField("flag"));
    
38.        b=getUnsafe().getBooleanVolatile(A.class, start);}
    
39.         catch(Exception e){}
    
40. return b;
    
41. }
    
42. }

复制代码