How Ruby Executes JIT Code: The Hidden Mechanics Behind the Magic
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Ruby's JIT compilers (YJIT and ZJIT) store compiled native code alongside original bytecode in Instruction Sequences (ISEQs). Ruby decides what to compile based on call frequency thresholds, first profiling methods after 25 calls, then compiling to native code after 30 calls. The execution switches between bytecode interpretation and native code execution by checking the jit_entry field. When assumptions break (like type changes or TracePoint activation), the JIT code falls back to the interpreter through de-optimization, ensuring correctness while maintaining performance benefits.
Table of contents
Where JIT-Compiled Code Actually LivesThe Execution Switch: From Bytecode to Native CodeHow Ruby Decides What to CompileAnswering Some Additional QuestionsFinal NotesSort: