You’d get a deadlock, absolutely. But I’m fine with that: if the thread wants to access some state protected by a mutex, then while holding it (effectively) spawns a signal handler activation and waits for it to complete, and the signal handler tries to accept some state protected by the same mutex, then the program has just deadlocked (mutex → signal handler → mutex) and deserves to hang (or die, as this is a very simple situation as far as deadlock detection goes). That’s in any case better than corrupted state.