You have misread what C++/Wikipedia says and are hence incorrect. The Wikipedia article says that actions are potentially concurrent if (they run from two diffe

You have misread what C++/Wikipedia says and are hence incorrect. The Wikipedia article says that actions are potentially concurrent if (they run from two different threads) OR (they are unsequenced AND one operation is performed by a signal handler). I have added the parenthesis to group together the logical clauses. Your omission of the requirement that the operation be performed from within a signal handler is significant and Wikipedia states the following about it: "The parts of this definition relating to signal handlers are idiosyncratic to C++ and are not typical of definitions of data race." Now we can definitely go into the nature of signal handlers in C++, but suffice it to say signal handlers are not considered to be executed from within the same thread as the main program. A signal handler is executed from within a special execution context that is independent of the rest of the program and whose behavior is distinct from typical threads. Suffice to say, other than specific idiosyncrasies, a signal handler is treated as if it were a separate thread of execution (even though technically an implementation does not have to actually spawn a separate thread for a signal handler).