In C++ this violates the data race rules both with and without volatile, but because it's sig_atomic_t it has a special carve out _only_ if it's volatile. See h

In C++ this violates the data race rules both with and without volatile, but because it's sig_atomic_t it has a special carve out _only_ if it's volatile. See https://eel.is/c++draft/basic#intro.races-22 https://eel.is/c++draft/basic#intro.races-22 C however states : > When the processing of the abstract machine is interrupted by receipt of a signal, the values of objects that are neither lock-free atomic objects nor of type volatile sig_atomic_t are unspecified, [...] The representation of any object modified by the handler that is neither a lock-free atomic object nor of type volatile sig_atomic_t becomes indeterminate when the handler exits. This wording is not present in C++, as it instead defines how signal handlers fit into the memory model. This means that (with adjustments for C atomics): int val = 0; std::atomic<bool> flag{false}; void handler(int sig) { if (!set) { val = 1; flag = true; } } int main(void) { signal(SIGINT, handler); while (!flag) { /* Spin waiting for flag */ } return val; } Is valid in C++, but not in C.