ractors

Ractors are a concurrency primitive in Ruby designed to enable parallel execution with strong memory isolation. Introduced to provide a safe path to true parallelism on multi-core systems, ractors allow Ruby code to run in separate, isolated execution contexts that do not share mutable state by default.

Each ractor runs in its own Ruby VM instance with its own heap. Objects crossing the boundary between ractors are not shared directly; data is copied or serialized as it moves between ractors. This isolation helps prevent data races and eliminates common threading hazards, but it also imposes a cost for inter-ractor communication and for using non-shareable resources.

Ractors communicate through a built-in message-passing mechanism. Programs create ractors, send messages to them, and receive responses. The typical workflow involves a ractor processing incoming messages, performing computations, and yielding results back to the sender or another ractor. Because of the isolation, most shared state and thread-local state are not directly accessible across ractors.

Usage considerations include performance trade-offs and library compatibility. While ractors enable parallelism beyond the Ruby GIL, they require that data crossing boundaries be shareable or serializable, and many standard libraries or external resources may not be fully compatible. There is also overhead from inter-ractor communication and from maintaining separate interpreters.

Ractors are part of Ruby’s broader approach to concurrent programming, offering a model closer to the actor paradigm. They complement threads by providing a means to execute code in parallel without sharing mutable state, at the cost of serialization and potential integration challenges.