Per discussion in #11492 (comment) per @yaauie observation:

Note that WorkerLoop.THREAD_CONTEXT is a ThreadLocal, so each java thread can pull its own ruby thread context out. The trouble arises if and when a java thread ever runs multiple ruby threads in the course of its lifetime (which I do not know), since we only populate it with ThreadLocal#withInitial and then use WorkerLoop.THREAD_CONTEXT in to pass a ThreadContext to various ruby internals that then use it to determine interrupt state.

This is the code in question:

We should investigate further into this.