Mutex, Take 3 (for "dumb" futex)

http://people.redhat.com/drepper/futex.pdf
("Mutex, Take 1" ... "Mutex, Take 2")

struct Mutex_Take_3 { // for "dumb" futex 

  futex lock; // 0: free, 1: locked, 3: contention

  void lock() {
    if (lock.atomic_bit_test_set(1)) 
      while (lock == 3 || lock.atomic_exchange(3))
        lock.wait(3);
  } 

  void unlock() {
    if (lock.atomic_exchange(0) == 3) 
      lock.wake(1);
  } 

}; // no CAS (long live "dumb" 386)

;-)

regards,
alexander.