You're certainly right that it's not the minimum amount of complexity. But it's not that hard to implement a simple MPMC queue (e.g. if you can assume DCAS on your platform) -- what's hard is making it fast. So part of the complexity derives from a design that calls for blocks of elements instead of a simlpe linked list, for example; but a lot of the speed comes from that design too.

The rest of the code size (and complexity) arises from the feature set (which I intended to be fairly complete): Users can provide tokens for better performance -- but don't have to. There's bulk methods. There's a move constructor and assignment operator (for the tokens too!). There's traits so that you can override the malloc/free that's used, and all the constants. There's memory debugging machinery (hidden in an #ifndef NEBUG). It all adds up, but not without reason, I think :-)

I will add a "how to read the code" section to the README later on when I have a minute. I think it would be instructive for those curious.