In this episode of Dead Code, Jared interviews Ivo Anjo, a Ruby performance expert at Datadog, about Ruby’s concurrency model and his work improving visibility into it. They discuss the Global VM Lock (GVL), which simplifies Ruby’s internals but hinders multithreading, and explore the promise and current limitations of M:N scheduling, now partially implemented via Ractors in Ruby 3.4. Ivo created the gvl-tracing gem to visualize thread behavior and uncover subtle bugs, advocating for a more intelligent, OS-like scheduler to improve performance fairness. He also shares insights from building Datadog’s always-on production profiler and his direct-bind gem, which allows low-level access to Ruby internals when official APIs fall short. Overall, the episode highlights a growing movement of developers modernizing Ruby’s internals and pushing past its reputation for being slow.

Links:

gvl-tracing

direct-bind

StackProf

rbspy

Ractors

YJIT

RubyConf

RubyKaigi

EuRuKo 2025

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