[pron]

Right, custom schedulers aren't quite ready for release yet -- there's a small missing piece in the VM that's required to fully preserve the spec, and they need a lot of testing that we don't yet have -- so we decided to go ahead without them and add them later.

[CHY872]

What’s the missing piece?

[pron]

A technical detail. Monitors (synchronized) record their owners as the OS thread, which makes the VM not know whether the carrier or the virtual thread owns a monitor, as they both share the same OS thread.

[CHY872]

For any future readers, I think this is the bug: https://bugs.openjdk.java.net/browse/JDK-8281642