Interview Question for Senior Software Engineer at Google:

//atomic increment function available
//input: A, B, C, D, E, F, G, ...,

static Semaphore BufferWrite;
// Data Structures
typedef my_spin_lock {
     uint64 next_ticket;
     uint64 cur_ticket;
}my_spin_lock_t;

my_spin_lock_t my_lock;
//Initialize

void initialize(my_spin_lock_t *my_lock)
{
    my_lock->cur_ticket = 1;
    my_lock->next_ticket = 0;
}

//spin lock
void spin_lock(....)
{
    uint64 temp;
    temp = atomic_increment(&my_lock->next_ticket);
    while (temp != my_lock->cur_ticket) spin_waiting();
}

CRITICAL SECTION

void spin_unlock(....)
{
     atomic_increment(&my_lock->cur_ticket);
}

//*****************************************//

void spin_lock(...){

    while(&my_lock->next_ticket){
           while(1){
                      wait(BufferWrite);
                       //Critical section
                      }
                   signal(BufferWrite);
               }
         }