[Animats]

Modern X86 machines do not quite have strong memory ordering. Loads may be reordered with older stores to different locations. This breaks some of the overly clever "lock free" algorithms:

http://bartoszmilewski.com/2008/11/05/who-ordered-memory-fen...

http://preshing.com/20120515/memory-reordering-caught-in-the...

This whole area is very touchy and easy to get wrong. Further reading:

https://software.intel.com/en-us/articles/tsx-anti-patterns-...