Not so weird after all

A presentation I gave at Xebia about some root cause analysis.

Transcript

1. Weird things can happen A tale on understanding documentation and undefined behavior
2. Just imagine •Your project is doing great! •Apple rolled out new language features •Lets use those features •Stuff just breaks (but only in production)
3. What’s going on here? •New release rolled out •Sudden increase by XXX % of “3 times wrong pin” occurrences •Sh#t hit the fan! Lots of users not happy!
4. Reproduction steps •Get a new or “factory reset” device •Install App •Register as usual •Logout •Login •Why is my pin not working? !$#%
5. Initial suspicions •It must’ve been a change we introduced in this release, right? •Right!?
7. Finding the problem •Well, sort of... it seems. •No joy during debugging. •Doesn’t crash on simulator •Doesn’t crash on our test devices when debugging
8. How can this break? •Why didn’t we see this before? •Why does it break now? •Putting back the old code “solves” it. •So that’s our initial bug fix.
9. Having that bad feeling •This doesn't feel right •This should not break!
10. Let’s go line by line
11. Let’s read some docs
12. Call in the cavalry •Some guy said to enable optimizations.. ;) •Let’s try that then...
14. Click, click, BOOM!!
15. What we learned