A simple data race in C11/C++11 is undefined behavior, it doesn't have to result in any well-defined state that you might get by interleaving the execution of t

A simple data race in C11/C++11 is undefined behavior, it doesn't have to result in any well-defined state that you might get by interleaving the execution of threads. I think this has been on HN already: http://www.hpl.hp.com/personal/Hans_Boehm/c++mm/why_undef.html http://www.hpl.hp.com/personal/Hans_Boehm/c++mm/why_undef.ht... Essentially it has to be that way, or on some architectures every access to a potentially shared variable would have to be wrapped in fences by the compiler.