关于++操作线程安全问题的疑惑

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关于++操作线程安全问题的疑惑5

public class TestSynchronizedThread  implements Runnable{

	private static Integer si = 0;

        private static AtomicInteger flag = new AtomicInteger();  
	
	@Override
	public void run() {
		for(int k=0;k<200000;k++){
			synchronized(si){
				si++;
			}
		}
	}
 public static void main(String[] args) throws InterruptedException{  
        TestMultiThread t1 = new TestMultiThread();  
        TestMultiThread t2 = new TestMultiThread();  
        ExecutorService exec1 = Executors.newCachedThreadPool();  
        ExecutorService exec2 = Executors.newCachedThreadPool();  
        exec1.execute(t1);  
        exec2.execute(t2);  
        while(true){  
            if(flag.intValue()==2){   
                System.out.println("si>>>>>"+si);           
                break;  
            }  
            Thread.sleep(50);  
        }  
  
          
    }  
}

这段代码最后结果si打印出来小于400000,为什么加了synchronized后++操作还会产生中间状态，而我在JVM字节码中并未找到相应的证据佐证。
下面是主要JVM字节码：

   0:   iconst_0
   1:   istore_1
   2:   iload_1
   3:   ldc     #2; //int 200000
   5:   if_icmpge       55
   8:   getstatic       #3; //Field si:Ljava/lang/Integer;
   11:  dup
   12:  astore_2
   13:  monitorenter
   14:  getstatic       #3; //Field si:Ljava/lang/Integer;
   17:  astore_3
   18:  getstatic       #3; //Field si:Ljava/lang/Integer;
   21:  invokevirtual   #4; //Method java/lang/Integer.intValue:()I
   24:  iconst_1
   25:  iadd
   26:  invokestatic    #5; //Method java/lang/Integer.valueOf:(I)Ljava/lang/Integer;
   29:  dup
   30:  putstatic       #3; //Field si:Ljava/lang/Integer;
   33:  astore  4
   35:  aload_3
   36:  pop
   37:  aload_2
   38:  monitorexit
   39:  goto    49
   42:  astore  5
   44:  aload_2
   45:  monitorexit
   46:  aload   5
   48:  athrow
   49:  iinc    1, 1
   52:  goto    2
   55:  return

希望各位大侠能帮小弟指点一下迷津。