java – LoadLoad屏障真的有什么作用？

int a;
volatile int b;

如果线程1执行：

a = 5;
b = 6;

然后在这两个指令之间插入一个StoreStore屏障,“a”正在刷新回主存储器.

现在如果线程2：

if(b == 6)
 a++;

在其间插入一个LoadLoad屏障,我们保证如果新值’b’可见,那么新值’a’也是可见的.但实际上是如何实现的？ LoadLoad是否使CPU缓存/寄存器无效？或者只是指示CPU从CPU再次获取从volatile读取的变量的值？

我已经找到关于LoadLoad屏障的信息(http://gee.cs.oswego.edu/dl/jmm/cookbook.html)：

LoadLoad Barriers The sequence: Load1; LoadLoad; Load2 ensures that
Load1’s data are loaded before data accessed by Load2 and all
subsequent load instructions are loaded. In general,explicit LoadLoad
barriers are needed on processors that perform speculative loads
and/or out-of-order processing in which waiting load instructions can
bypass waiting stores. On processors that guarantee to always preserve
load ordering,the barriers amount to no-ops.

但它并没有真正解释这是如何实现的.