[dnedic]

True, that would help immensely in creating MPMC data structures, but as these are SPSC there is no problem. Also to clarify, this is only for the indexes, the data members can be anything.

Using these intrinsics or inline assembly would break portability or create situations where platforms have different feature levels, which is not something I intend to do. I want the library to be compatible with everything from a tiny MCU to x86.

[hedora]

I've had good luck assuming double-word CAS, portability-wise. Old ARMs have 32 bit pointers, so 64 bit CAS is pretty good. The main problem is that some algorithms go from a bit under 64 bits for a nonce to a bit under 32, which starts to get into "this could hit in practice" territory.