io.vertx.redis.client.impl.ArrayQueue Maven / Gradle / Ivy
/*
* Copyright 2019 Red Hat, Inc.
*
* All rights reserved. This program and the accompanying materials
* are made available under the terms of the Eclipse Public License v1.0
* and Apache License v2.0 which accompanies this distribution.
*
* The Eclipse Public License is available at
* http://www.eclipse.org/legal/epl-v10.html
*
* The Apache License v2.0 is available at
* http://www.opensource.org/licenses/apache2.0.php
*
* You may elect to redistribute this code under either of these licenses.
*/
package io.vertx.redis.client.impl;
import java.util.NoSuchElementException;
final class ArrayQueue {
private int
cur, // current number of elements
front, // front index
back; // back index
private final Object[] queue;
/**
* Creates a new empty queue.
*/
ArrayQueue(int capacity) {
queue = new Object[capacity];
back = -1;
front = 0;
}
/**
* Tests if the queue is logically empty.
*
* @return true if the queue is empty and false otherwise
*/
boolean isEmpty() {
return cur == 0;
}
/**
* Puts a value into the back of the queue. It works with wraparound.
* If the queue is full, it doubles its size.
*
* @param value the item to insert.
* @throws IndexOutOfBoundsException if the queue is full.
*/
void offer(T value) {
if (isFull()) {
throw new IndexOutOfBoundsException();
}
back++;
if (back == Integer.MAX_VALUE) {
// ensure the indexes stay positive
back = 0;
}
queue[back % queue.length] = value;
cur++;
}
/**
* Returns the first element in the queue.
*
* @return element at front of the queue, null if empty.
*/
T peek() {
if (isEmpty()) {
return null;
} else {
return (T) queue[front % queue.length];
}
}
/**
* Returns and removes the front element of the queue. It works with wraparound.
*
* @return element at front of the queue
* @throws NoSuchElementException if the queue is empty.
*/
T poll() {
T e = peek();
queue[front % queue.length] = null; // for garbage collection
front++;
if (front == Integer.MAX_VALUE) {
// ensure the indexes stay positive
front = 0;
}
cur--;
return e;
}
int freeSlots() {
return queue.length - cur;
}
/**
* Tests if the queue is logically full
*/
boolean isFull() {
return cur == queue.length;
}
}