Start using a C hash table library for processing sentinel responses

[TysonAndre]

Either that or loop against all of the expected key values and append the matches to corresponding lists, then processing the lists.

Twemproxy currently does the sentinel response processing in a loop; it's highly sensitive to order, and hardcodes assumptions about how many lines there are.

https://github.com/attractivechaos/klib (MIT) may be promising; I haven't worked with it before.

this would prevent bugs similar to the following:

#8
#6

Even #6 continues to assume lines will be in the expected order