Virtual Thread Pinning: The Hidden Performance Killer in Java Loom

A service migrated to virtual threads plateaued at 420 requests per second on an 8-core machine due to pinning, where virtual threads block carrier threads. Pinning occurs only in two scenarios: blocking inside synchronized blocks (JDK 21-23) or native frames. JDK 24 fixes the synchronized case but not native frames, leaving developers vulnerable to scheduler starvation.