How does Ruby manage memory visibility and consistency under GVL during thread switching?

GVL acts as a global synchronization barrier ensuring memory consistency during thread switches.

When a thread releases the GVL, Ruby ensures all writes to VM-managed memory are visible to other threads by relying on OS-level memory barriers and GVL acquisition semantics. Since only one thread executes Ruby bytecode at a time, race conditions in VM state are avoided. However, external C extensions or system calls can bypass this guarantee, requiring explicit synchronization.