Polyphony is a library for writing highly concurrent Ruby apps. Polyphony harnesses Ruby fibers and a powerful io_uring-based I/O runtime to provide a solid foundation for building high-performance concurrent Ruby apps, while letting developers use stock Ruby core and stdlib classes and APIs. In order for provide a solid developer experience, Polyphony reimplements different parts of the Ruby runtime functionality, which are adjusted so developers will see a consistent and reliable behaviour. My latest article discusses the problem of signal handling in concurrent Ruby apps.