This document discusses several key aspects of how Ruby works under the hood. It explains that Ruby is an interpreted language that uses a virtual machine to execute bytecode. It describes the Ruby interpreter and how it implements a stack-based virtual machine to map bytecodes to native instructions. It also discusses Ruby's memory management through garbage collection, describing the mark-and-sweep algorithm as a simple example of how garbage collection works.

1. Ruby Under the Hood
Robert Young Craig Lehmann
Crob 2015

2. What’s under the hood?
Reading your source
understanding your program
memory management

3. What’s under the hood?
Ruby is an Interpreted language.

4. Program Parsing

5. Syntax Tree

6. The ruby Interpreter?
The Ruby interpreter implements a virtual machine.

7. Bytecode Interpreter
The main VM execution loop.
Maps bytecodes to executable native instructions.
Implements a virtual stack machine.
Individual bytecodes implemented in C.

8. s

9. Push down Stack

10. Call Stack example and compiled method

11. Three Stacks

12. Control Frame Data Structure

13. Class lookup? What happens when you want to create an
object?
class Person
end
arbitraryConstant = "zZz"

14. A class is listed in a datastructure full of constants
class Person
end
arbitraryConstant = "zZz"

15. A class is listed in a datastructure full of constants

16. constants with the same name as a class? That’s a No No
class Person
end
Person = "hello"
# warning: already initialized constant Person

17. Intro to GC
What is garbage collection
Example of how a simple GC algorithm

18. What is garbage collection?
Automatic memory management

19. What is garbage collection?
Allocate and free objects
Keep track of objects currently in use
Run finalizers

20. A simple GC example - Mark and Sweep

21. A simple GC example - Mark and Sweep

22. A simple GC example - Mark and Sweep

23. A simple GC example - Mark and Sweep

24. A simple GC example - Mark and Sweep

25. A simple GC example - Mark and Sweep

26. A simple GC example - Mark and Sweep

27. A simple GC example - Mark and Sweep