// Page 150 example doesn't work
// This fixes it.
import java.util.concurrent.atomic.AtomicInteger;
import java.util.concurrent.atomic.AtomicIntegerArray;

public class Alock implements SimpleLock {
    final static ThreadLocal<Integer> mySlotIndex = new ThreadLocal<Integer>();
    final AtomicInteger tail = new AtomicInteger(0);
    AtomicIntegerArray flag;
    public Alock() { flag = null; }
    public void init(int th) {
        flag = new AtomicIntegerArray(th);
        for(int i=0;i<th;i++) {
            flag.set(i,(i == 0) ? 1 : 0);
        }
    }
    public void lock() {
        int slot = tail.getAndIncrement() % flag.length();
        mySlotIndex.set(slot);
        assert slot < flag.length();
        while(flag.get(slot)==0) {
          Thread.yield();
        }
    }
    public void unlock() {
        int slot = mySlotIndex.get();
        flag.set(slot, 0);
        int next = (slot+1)%flag.length();
        flag.set(next, 1);
    }
    public void finish() {}

    public String name() { return getClass().getName(); }
}