CryChat/crychat/server/util/Queue.java

package server.util;

/*
    !!! WORK IN PROGRESS !!!

    trying to implement a wait-free queue
 */

import java.util.concurrent.atomic.AtomicReferenceArray;

public class Queue<T> {

    private volatile int head = 0, tail = 0;
    private final int capacity;
    private AtomicReferenceArray<T> items;

    public Queue(int capacity) {
        this.capacity = capacity;
        items = new AtomicReferenceArray<>(capacity);
    }

    public boolean enq(T x) {
        if (tail - head == capacity) return false;
        items.set((tail + 1) % capacity, x);
        tail++;
        return true;
    }

    public T deq() {
        if (tail - head == 0) return null;
        T x = items.get((head + 1) % capacity);
        head++;
        return x;
    }
}