Unicorns Die With Bullets Made of Glitter

The reduced, 30 minutes version of this collection of Ruby Systems Horror Stories, including:

- Mark & Sweep, a tale of a dumb garbage collector
- Our Time is Running Out, a tale of tricky timeouts

Originally presented at Rubyfuza.

Transcript

2. Once upon a time…
4. These are horror stories from the GitHub Systems team (the rainbows are just to make them less awful)
5. I HAVE A LOT OF SPARE TIME
6. Ogre Magi is (C) 2013 by Valve Software and takes 0 skill to play
7. Mark Sweep The Garba e Collector
8. Garba e Collector
9. Conservative Garba e Collector
10. Conservative Garba e Collector Non-deterministic
11. Conservative Stop The World Garba e Collector Non-deterministic
12. Conservative Stop The World Mark and Sweep Garba e Collector Non-deterministic
13. Conservative Stop The World Mark and Sweep Garba e Collector Non-deterministic Basically a shitshow.
15. Mark
16. Mark 1. Walk the object raph 2. Look for thin s that look like Ruby objects
18. Ruby handles raw pointers to C extensions.
19. Ruby handles raw pointers to C extensions. The Garba e Collector must find roots in the stack, the heap and in re isters.
21. “This kinda looks like a pointer”
22. “This kinda looks like a pointer” “I uess…”
23. “This kinda looks like a pointer” “I uess…” *dramatization
25. Sweep
26. Sweep 1. Go throu h every sin le object 2. Free the ones that have not been marked
28. The Problem
29. The Problem There is memory allocated by Ruby that the Ruby GC cannot detect.
30. char * VALUE * … … RStrin MAGICAL RUBY THINGS int a_ruby_function(VALUE rb_foo) { char *str = RSTRING_PTR(rb_foo); return do_smthing(str); }
31. char * VALUE * … … RStrin MAGICAL RUBY THINGS int a_ruby_function(VALUE rb_foo) { char *str = RSTRING_PTR(rb_foo); return do_smthing(str); } H e l l o W o r l d \0
32. char * … … H e l l o W o r l d \0 int do_smthing(char *str) { /* do stuff */ return strlen(str); }
33. int do_smthing(char *str) { /* do stuff */ return strlen(str); } Un ! Un ! Mark o throu h stack. Yes. Stack.
34. Un ! This no look like Ruby object. Mark no touchie! char * … … … H e l l o W o r l d \0
35. No root. H e l l o W o r l d \0 RStrin MAGICAL RUBY THINGS Strin object with no roots? Set fire. Yes. Fire.
36. No root. H e l l o W o r l d \0 Strin object with no roots? Set fire. Yes. Fire.
37. No root. Strin object with no roots? Set fire. Yes. Fire.
38. int do_smthing(char *str) { /* do stuff */ return strlen(str); }
39. int do_smthing(char *str) { /* do stuff */ return strlen(str); } *sound of an explosion* “What was that?” “Dunno.”
40. HAPPY ENDINGS: (sorry about this slide)
41. 1. Drink Yourself To Sleep Every Ni ht
42. 2. Stress the Garba e Collector in Critical Paths
44. mallopt(M_PERTURB, 0x33); C land
45. mallopt(M_PERTURB, 0x33); C land GC.stress = true Ruby land
46. Bonus Points Use Val rind/ASan instead of tamperin .
47. Bonus Points Use Val rind/ASan instead of tamperin . Your Rails test suite Heat death of the Universe
48. 3. Static Analysis
50. How do you feel about timeouts?
51. THERE ARE NO TIMEOUTS IN RUBY (just ask the Timeout Rabbit)
52. require ‘timeout’
53. require ‘timeout’ Timeout::timeout(5) { # Do something }
54. require ‘timeout’ Timeout::timeout(5) { # Do something } …
56. …
57. … …
58. … … oh hey
59. “Sorry I’m late. Couldn’t et here any faster.”
61. Beautiful
62. Beautiful wron also:
63. MRI 1.8.7 Ruby Process Green Thread Green Thread Green Thread THE KERNEL
64. MRI 1.9.3 Ruby Process THE KERNEL NNative Thread NNative Thread NNative Thread
65. MRI 1.9.3 Ruby Process THE KERNEL NNative Thread NNative Thread NNative Thread GVL
66. Use the force, kid
67. “Unix, you moron. Unix is the force.”
68. “Unix, you moron. Unix is the force.”
70. MRI 1.8.7 Use si nals & the power of Unix
71. MRI 1.8.7 Use si nals & the power of Unix MRI 1.9.3 Release the GVL
72. Mathiasman the Wise
76. “I, too, had a dreadful problem with timeouts”
77. You see, I was usin JRuby…
78. JRuby? Sounds like you have two problems now.
79. (shut up, kid) You see, I was usin JRuby, and the GitHub API you uys keep breakin …
80. Duh. That’s probably because the thread is sleepin or stuck in the GVL.
81. You fool! JRuby has native threads and fine- rained lockin ! *smack*
82. JRUBY 1.6.7 Timeout::timeout(5) { Timeout::timeout(60) { # Do something } } Lon est timeout clobbers the short one
83. JRUBY 1.6.7 Timeout::timeout(5) { Timeout::timeout(60) { # Do something } } Lon est timeout clobbers the short one
84. I LIKE THIS BUG Because JRuby wins
85. Simple Bu Complex Bu Painful Bu Kernel Bu NESTED TIMEOUTS IN THE JVM
86. Now Leavin : Realm of Bu s Valley of Common Sense
87. mmon Sense Mountains of Reason
88. Country of WHAT THE HELL ARE YOU DOING MRI Timeouts in Green Threads
89. MORAL OF THE STORY
90. BETTER WORSE IS Sometimes *this doesn’t apply to the MRI GC
91. Computers break Ruby breaks twice as often
92. If you build simpler systems, they will break in simpler ways.