Ruby Under the Hood

Robert Young Craig Lehmann

Crob 2015

What’s under the hood?

I Reading your source

I understanding your program

I memory management

What’s under the hood?

Ruby is an Interpreted language.

Program Parsing

Syntax Tree

The ruby Interpreter?

The Ruby interpreter implements a virtual machine.

Bytecode Interpreter

I The main VM execution loop.

I Maps bytecodes to executable native instructions.

I Implements a virtual stack machine.

I Individual bytecodes implemented in C.

s

Push down Stack

Call Stack example and compiled method

Three Stacks

Control Frame Data Structure

Class lookup? What happens when you want to create anobject?

class Person

end

arbitraryConstant = "zZz"

A class is listed in a datastructure full of constants

class Person

end

arbitraryConstant = "zZz"

A class is listed in a datastructure full of constants

constants with the same name as a class? That’s a No No

class Person

end

Person = "hello"

# warning: already initialized constant Person

Intro to GC

I What is garbage collection

I Example of how a simple GC algorithm

What is garbage collection?

I Automatic memory management

What is garbage collection?

I Allocate and free objectsI Keep track of objects currently in use

I Run finalizers

A simple GC example - Mark and Sweep

A simple GC example - Mark and Sweep

A simple GC example - Mark and Sweep

A simple GC example - Mark and Sweep

A simple GC example - Mark and Sweep

A simple GC example - Mark and Sweep

A simple GC example - Mark and Sweep

A simple GC example - Mark and Sweep