On Wed, 3 Dec 2025 13:34:40 GMT, Jorn Vernee <[email protected]> wrote:
>> Looking at this, I'm not sure we can assume that we only see one mode and
>> type when the VH is constant. There seems to be a lot of non-local reasoning
>> involved.
>>
>> For example, you could have a var handle invoker created with
>> `MethodHandless::varHandleInvoker`, which is cached, so the
>> `AccessDescriptor` can be shared among many different use sites. For an
>> individual use-site, the receiver VH may well be a constant, but that
>> doesn't mean that the cache isn't polluted by the var handle from another
>> use site, as far as I can tell.
>>
>> The thread safety issue comes from a C2 thread racing to read the
>> `lastAdaption` cache vs another Java thread writing to the cache. AFAICS,
>> this race is still possible even when `vh` is a compile time constant.
>
> I think even without using an invoker, you could end up in a similar
> situation if you have something like:
>
>
> static Object m(VarHandle vh) {
> return vh.get();
> }
>
>
> Which is called by several different threads. At some point this method may
> be inlined into one of its callees, where `vh` then becomes a constant. But
> at the same time, other threads are still writing to the cache.
This issue should have been fixed, and there's a unit test to verify.
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PR Review Comment: https://git.openjdk.org/jdk/pull/28585#discussion_r2596829589
