基于AQS+双向链表实现队列先进先出

学习AQS写的一个模拟案例

package com.tom.xiangyun.ch04_aqs;import com.tom.tuling.UnsafeFactory;
import sun.misc.Unsafe;import java.util.concurrent.atomic.AtomicInteger;
import java.util.concurrent.locks.ReentrantLock;/*** 使用双向链表实现队列** @author 钟棋炜* @date 2023-08-22 20:52*/
public class QueueDoubleLinked {private transient volatile Node head;private transient volatile Node tail;private static final Unsafe unsafe = UnsafeFactory.getUnsafe();private static final long headOffset;private static final long tailOffset;private static final long nextOffset;private final ReentrantLock takeLock = new ReentrantLock();private final AtomicInteger count = new AtomicInteger();static {try {assert unsafe != null;headOffset = unsafe.objectFieldOffset(QueueDoubleLinked.class.getDeclaredField("head"));tailOffset = unsafe.objectFieldOffset(QueueDoubleLinked.class.getDeclaredField("tail"));nextOffset = unsafe.objectFieldOffset(Node.class.getDeclaredField("next"));} catch (Exception ex) {throw new Error(ex);}}public QueueDoubleLinked() {}private  boolean compareAndSetHead(Node update) {return unsafe.compareAndSwapObject(this, headOffset, null, update);}private boolean compareAndSetTail(Node expect, Node update) {return unsafe.compareAndSwapObject(this, tailOffset, expect, update);}//入队public String add(String element) {Node node = new Node(element);enq(node);return element;}//出队 先进public Object poll() {final AtomicInteger count = this.count;if (count.get() == 0) {return null;}Object x = null;final ReentrantLock takeLock = this.takeLock;takeLock.lock();try {if (count.get() > 0) {x = dequeue();count.getAndDecrement();}} finally {takeLock.unlock();}return x;}private Object dequeue() {Node h = head;Node first = head.next;h.next = h;head = first;Object obj = first.data;first.data = null;return obj;}private Node enq(final Node node) {//尾插法final AtomicInteger count = this.count;for (; ; ) {Node t = tail;if (t == null) {if (compareAndSetHead(new Node())) {tail = head;}} else {node.prev = t;if (compareAndSetTail(t, node)) {t.next = node;count.getAndIncrement();return t;}}}}static final class Node {Node prev;//前置节点Node next;//后置节点Object data; //存放数据public Node() {}public Node(Object data) {this.data = data;}}public static void main(String[] args) {QueueDoubleLinked queue = new QueueDoubleLinked();queue.add("tom");queue.add("no");queue.add("xx");queue.add("zz");System.out.println(queue.poll());System.out.println(queue.poll());System.out.println(queue.poll());System.out.println(queue.poll());System.out.println(queue);}
}