test.cpp

class AutoMutex {
 public:
  inline AutoMutex() : mLockCount(0) {
    int expected = 0;
    __c11_atomic_compare_exchange_weak(&mLockCount, &expected, expected + 1,
                                       __ATOMIC_SEQ_CST, __ATOMIC_SEQ_CST);
  }

 private:
  char x[128];
  _Atomic(int) mLockCount;
};

void flush(void) {
  AutoMutex mtx;
}