[esrauch]

Protobuf is the example I had in mind. It uses sun.misc.Unsafe which is being removed in upcoming Java releases, but it has a slow fallback path. It logs a warning when it runs if it can tell it's only using the fallback path but the fast path is still available if the application owner set a flag to turn it back on if they want to:

https://github.com/protocolbuffers/protobuf/issues/20760

Java Protobuf also logs a warning now if you can tell you are using gencode old enough that it's covered by a DoS CVE. They actually did a release that broke compatability of the CVE covered gencode but restored it and print a warning in a newer release.

[vips7L]

What’s stopping you from using the replacements provided in VarHandle and MemorySegment? Just wanting to support the 10 year old JDK 8?

[esrauch]

There's a lot here, to be honest these things always come back to investment cost and ROI compared to everything else that could be worked on.

Java 8 is still really popular, probably the most popular single version. It's not just servers in context, but also Android where Java 8 is the highest safe target, it's not clear what decade we'll be in when VarHandle would be safe to use there at all.

VarHandle was Java 9 but MemorySegment was Java 17. And the rest of FFM is only in 25 which is fully bleeding edge.

Protobuf may realistically try to move off of sun.misc.unsafe without the performance regressions in a way that is without adopting MemorySegment to avoid the versioning problem, but it takes significant and careful engineering time.

That said it's always possible to have waterfall of preferred implementations based on what's supported, it's just always an implementation/verification costs.