Gaurav Varma

Ruby 3.0 is a landmark release that brings the language closer to real concurrency with two significant additions: Ractors and the Fiber scheduler. These features aim to improve performance and scalability, all while preserving Ruby’s friendly syntax.

Why concurrency matters

As applications scale and hardware becomes more multi-core, concurrency becomes crucial for performance. Ruby’s traditional thread-based model is limited by the Global VM Lock (GVL), making true parallel execution difficult. Ruby 3.0 introduces abstractions to overcome this.

Ractors: Parallelism without thread-safety headaches

Ractor (short for "Ruby Actor") is a new concurrency abstraction that enables parallel execution without sharing mutable state.

Key features:

Each Ractor has isolated memory.
Communication is done via message passing.
Designed to work around the GVL.

1r = Ractor.new { 1 + 2 }
2puts r.take # => 3

Ractors introduce syntax restrictions to enforce safety, but allow Ruby code to run in true parallel threads.

Fiber Scheduler: Lightweight, non-blocking I/O

Fiber scheduler provides a hookable API that allows libraries like async to intercept blocking operations such as sleep or I/O.

This enables cooperative multitasking, where operations yield control rather than block the thread.

1require 'async'
2require 'net/http'
3
4Async do
5  ["https://ruby-lang.org", "https://rails.org"].each do |url|
6    Async do
7      Net::HTTP.get(URI(url))
8    end
9  end
10end

This code performs multiple HTTP requests concurrently, using async fibers under the hood.

Benefits

Better CPU utilization on multi-core systems
No more thread-safety concerns
Improved performance for I/O-heavy workloads
Works with gems like async, falcon, net/http, and more

Status and compatibility

Ractors are marked as experimental.
Fiber scheduler is opt-in and requires compatible libraries.
Both features are evolving rapidly, and more improvements are expected in Ruby 3.1+.

Resources

Summary

Ruby 3.0 marks a turning point for concurrency. With Ractors enabling parallelism and Fiber scheduler unlocking non-blocking I/O, developers can write scalable, performant Ruby code while maintaining the joy and simplicity that makes Ruby shine.

Ruby 3.0 introduces Ractors and Fiber scheduler for real concurrency