Slides describing high level overview of Ruby internals.

1. About me
1
Guelph ES&C Grad – spring 2014
Currently employed at IBM as a
Runtime Technologies Software Dev
Twitter: @craiglehmann

2. Ruby Under The Hood
http://lolsnaps.com/upload_pic/EveryTimeILookUnderThe
HoodOfACar-97946.jpg

3. Program compilation
3

4. Program compilation
4

5. Program compilation
5

6. Program compilation
6
3.times do |n|
puts n
end

7. Program compilation
7
Tokens:
3.times do |n|
puts n
end puts
ndo
end
3 dot times

8. Program compilation
8
AST
3.times do |n|
puts n
end
puts n
3 times
call
block
command

9. Program compilation
9

10. The Ruby Interpreter?
The Ruby Interpreter implements a virtual machine.
10

11. Bytecode Interpreter
 The main VM execution loop.
 Maps bytecodes to executable native instructions.
 Implements a virtual stack machine.
 Individual bytecodes implemented in C.
11

12. 12
Ruby is a Stack Machine!

13. Push Down Stack
13
1 + 2

14. Push Down Stack
14
1 + 2 Push 1
Push 2
opt_plus
Bytecodes:

15. Push Down Stack
15
1 + 2 Push 1
Push 2
opt_plus
Bytecodes:
1
Push 1

16. Push Down Stack
16
1 + 2 Push 1
Push 2
opt_plus
Bytecodes:
1
Push 1
2
Push 2
1

17. Push Down Stack
17
1 + 2 Push 1
Push 2
opt_plus
Bytecodes:
1
Push 1
2
Push 2
3
opt_plus
1

18. Call Stack example and compiled method
18
def do_things
puts "Hello World"
end
Putself
Putstring “Hello World”
opt_send_simple

19. Three Stacks
19
def do_things
puts "Hello World"
end
Putself
Putstring “Hello World”
opt_send_simple
C Stack VM Stack Ruby Call Stack

20. Call Stack example and compiled method
20
def do_things
puts "Hello World"
end
Putself
Putstring “Hello World”
opt_send_simple
call_method
C Stack
exec_core
…
main()
VM Stack Ruby Call Stack

21. Call Stack example and compiled method
21
def do_things
puts "Hello World"
end
Putself
Putstring “Hello World”
opt_send_simple
call_method
C Stack
exec_core
…
main()
opt_send_simple puts
VM Stack
“hello World”
self
Ruby Call Stack

22. Call Stack example and compiled method
22
def do_things
puts "Hello World"
end
Putself
Putstring “Hello World”
opt_send_simple
call_method
C Stack
exec_core
…
main()
opt_send_simple puts
VM Stack
“hello World”
self
puts
Ruby Call Stack
do_things

23. Three Stacks
23
call_method
C Stack
exec_core
…
main()
opt_send_simple puts
VM Stack
“hello World”
self
puts
Ruby Call Stack
do_things

24. What does this look like in the Ruby’s VM?
24
puts
Ruby Call Stack
do_things
def do_things
puts "Hello World"
end

25. What does this look like in the Ruby’s VM?
25
puts
Ruby Call Stack
do_things
def do_things
puts "Hello World"
end
PC
Control Frame
SP
Self
type

26. What does this look like in the Ruby’s VM?
26
puts
Ruby Call Stack
do_things
def do_things
puts "Hello World"
end
PC
Control Frame
SP
Self
type
putself
putstring “Hello World”
opt_send_simple

27. What does this look like in the Ruby’s VM?
27
puts
Ruby Call Stack
do_things
def do_things
puts "Hello World"
end
PC
Control Frame
SP
Self
type
putself
putstring “Hello World”
opt_send_simple
opt_send_simple puts
VM Stack
“hello World”
self

28. Class lookup? What happens when you want to create
an object?
28
class Person
end
p = Person.new()

29. Class lookup? What happens when you want to create
an object?
29
class Person
end
p = Person.new()

30. Class lookup? What happens when you want to create
an object?
30
class Person
end
p = Person.new()
Person = "Craig"
#Warning: already initialized constant person

31. Intro to garbage collection
What is garbage collection?
Different types of garbage collection algorithms
Mark & Sweep demo
31

32. 32
What is garbage collection?
 Automatic memory management
 Manually managing memory is hard!
 Aggregate freeing memory & object destruction operations
 Gives the illusion of unlimited memory

33. 33
Different types of garbage collection algorithms
 Reference Counting
• Keep a count along with each object indicating how many references it currently
has. An object with 0 references can have it's memory re-used.
• Cannot manage cyclically referenced objects.
 Tracing Algorithms
• keep track of which objects are in use by recursively tracing objects referring to
other objects, starting from a root set of objects.

34. What does it mean to die
• An object consumes one resource, memory.
• When an object becomes unreachable, it can never be used again.
• Cycles are collected together, the mutator cannot access these
object.
• Sweeping objects means adding it’s memory to a list for reuse.
• What about when an object consumes more than just one resource?
34

35. Mark and Sweep Demo
35

36. Mark and Sweep Demo
36

37. Mark and Sweep Demo
37

38. Mark and Sweep Demo
38

39. Mark and Sweep Demo
39

40. Mark and Sweep Demo
40

41. Mark and Sweep Demo
41

42. Mark and Sweep Demo
42

43. Object Finalization
• Some objects may have operations that need to occur pre/post
collection
• e.g. file object
43

44. Execution Environment
Architecture of a Managed Runtime
44
Platform Abstraction Layer
Garbage Collector
Diagnostic Services
Source Code Bytecode/AST
Compiler
Just-In-Time Compiler
Interpreter

45. Execution Environment
Architecture of a Managed Runtime
45
Platform Abstraction Layer
Garbage Collector
Diagnostic Services
Source Code Bytecode/AST
Compiler
Just-In-Time Compiler
Interpreter

46. Execution Environment
Architecture of a Managed Runtime
46
Platform Abstraction Layer
Garbage Collector
Diagnostic Services
Source Code Bytecode/AST
Compiler
Just-In-Time Compiler
Interpreter

47. Execution Environment
Architecture of a Managed Runtime
47
Platform Abstraction Layer
Garbage Collector
Diagnostic Services
Source Code Bytecode/AST
Compiler
Just-In-Time Compiler
Interpreter
 Interpreter context
 Thread context
 Language callstack

48. Execution Environment
Architecture of a Managed Runtime
48
Platform Abstraction Layer
Garbage Collector
Diagnostic Services
Source Code Bytecode/AST
Compiler
Just-In-Time Compiler
Interpreter

49. Execution Environment
Architecture of a Managed Runtime
49
Platform Abstraction Layer
Garbage Collector
Diagnostic Services
Source Code Bytecode/AST
Compiler
Just-In-Time Compiler
Interpreter

50. Execution Environment
Architecture of a Managed Runtime
50
Platform Abstraction Layer
Garbage Collector
Diagnostic Services
Source Code Bytecode/AST
Compiler
Just-In-Time Compiler
Interpreter

51. Thank You!
Twitter: @craigLehmann
Email: craigl@ca.ibm.com