RFR 8155258: VarHandle implementation improvements

[Paul Sandoz]

> On 4 May 2016, at 09:19, Vladimir Ivanov <vladimir.x.ivanov at oracle.com> wrote:
> 
> Looks good.
> 
> I'm fine with pushing it directly into jdk9/dev, since the change just relaxes the assert and the risk of a merge conflict is very small.
> 

Thanks!


> Best regards,
> Vladimir Ivanov
> 
> PS: I wonder whether the MH cache in VarHandle (VarHandle.typesAndInvokers.methodHandle_table) should be idempotent or not.
> 

I am guessing you mean in terms of the MH ref identity?


> In the past, we had to make some caches in j.l.i idempotent (specifically, Invokers.invokers and MethodTypeForm.methodHandles).
> 
> The problem was that the JVM can cache a method the MH points to (e.g., inline caches in generated code for MH invokers). If it happens, the JVM doesn't expect to observe 2 different instances of the MH, otherwise an assertion is fired.
> 
> I can't say for sure it's not the case for VarHandles as well.
> 

Ok, i will take a closer look at the existing caches (i did look at those for inspiration) and follow up. I might need to synchronise the update.

FWIW there are also cases in MethodHandleImpl where MHs are cached without synchronization, perhaps such constraints don’t matter in these cases?

Paul.