How does Ruby handle global state consistency across threads under GVL?

GVL ensures only one thread mutates global VM state at a time, maintaining consistency without fine-grained locks.

Global VM structures like method tables, constants, and GC state are protected by GVL. This eliminates need for per-object locks. However, when threads perform blocking I/O, GVL is released, so Ruby relies on atomic VM transitions and careful re-acquisition to avoid inconsistent states. This simplifies design but limits CPU parallelism.