> one global `sig_atomic_t end_flag = 0;`, a single writer (a SIGINT handler to set it to 1), and many threads with `while (end_flag == 0) { ... }` loops. Whil

> one global `sig_atomic_t end_flag = 0;`, a single writer (a SIGINT handler to set it to 1), and many threads with `while (end_flag == 0) { ... }` loops. While unlikely to cause problems, this is a data race (a set of at least two concurrent accesses, of which at least one is not an atomic access and at least one is a write) and therefore constitutes undefined behavior. sig_atomic_t is only safe to use from one thread, where concurrency is given by a signal handler.