RFR: 8332547: Unloaded signature classes in DirectMethodHandles

[Vladimir Ivanov]

On Mon, 20 May 2024 21:29:20 GMT, Vladimir Ivanov <vlivanov at openjdk.org> wrote:

> JVM routinely installs loader constraints for unloaded signature classes when method resolution takes place. MethodHandle resolution took a different route and eagerly resolves signature classes instead (see `java.lang.invoke.MemberName$Factory::resolve` and `sun.invoke.util.VerifyAccess::isTypeVisible` for details). 
> 
> There's a micro-optimization which bypasses eager resolution for `java.*` classes. The downside is that `java.*` signature classes can show up as unloaded. It manifests as inlining failures during JIT-compilation and may cause severe performance issues.
> 
> Proposed fix removes the aforementioned special case logic during `MethodHandle` resolution. 
> 
> In some cases it may slow down `MethodHandle` construction a bit (e.g., when repeatedly constructing `DirectMethodHandle`s with lots of arguments), but `MethodHandle` construction step is not performance critical.  
> 
> Testing: hs-tier1 - hs-tier4

Class loading triggered by `Class.forName()` call is at the core of `isTypeVisible`. (The rest is fast path checks.) It's what makes `isTypeVisible` query idempotent. 

I can definitely name it differently (e.g, `ensureTypeVisible`), but making a separate class loading pass across signature classes doesn't make much sense.

-------------

PR Comment: https://git.openjdk.org/jdk/pull/19319#issuecomment-2123160245