loop invariant code motion and the jit

[Andrew Haley]

On 18/01/17 20:04, Peter Veentjer wrote:
> private boolean stop;
> private long value;
> 
> @Override
> public void run() {
>     while (!stop) {
>         value++;
>     }
> }
> 
> In theory the read of stop can be pulled out of the loop since stop isn't
> properly synchronised (volatile would do the trick).

In practice, too.

> Is there any prevention of this optimisation being applied to protect users
> against improper synchronised code?

No.  If you want this to work properly, use a Reference or (in JDK9) a
VarHandle or a Fence.

Andrew.