Explicitly pin a virtual thread before acquiring the JFR string pool monitor because migrating a carrier thread local event writer object onto another carrier thread is impossible.

During event commit, the thread is in a critical section because it has loaded a carrier thread local event writer object. For virtual threads, a contended monitor, such as a synchronized block, is a point where a thread could become unmounted.

A monitor guards the JFR string pool, but remounting a virtual thread onto another carrier is impossible because of the event writer.

Therefore, it's imperative to use explicit pin constructs to prevent unmounting at this location.