序

ConcurrentLinkedQueue是一个基于链接节点的无界线程安全队列，它采用先进先出的规则对节点进行排序，当我们添加一个元素的时候，它会添加到队列的尾部，当我们获取一个元素时，它会返回队列头部的元素。

对比

实例

由于ConcurrentLinkedQueue是无界的，所以使用的时候要特别注意内存溢出问题。akka的actor模型，默认的mailbox是用这个来实现的。

object UnboundedMailbox {
  class MessageQueue extends ConcurrentLinkedQueue[Envelope] with UnboundedQueueBasedMessageQueue {
    final def queue: Queue[Envelope] = this
  }
}

MyUnboundedMailbox

public class MyUnboundedMailbox implements MailboxType,
  ProducesMessageQueue<MyUnboundedMailbox.MyMessageQueue> {

  // This is the MessageQueue implementation
  public static class MyMessageQueue implements MessageQueue,
      MyUnboundedMessageQueueSemantics {
    private final Queue<Envelope> queue =
      new ConcurrentLinkedQueue<Envelope>();

    // these must be implemented; queue used as example
    public void enqueue(ActorRef receiver, Envelope handle) {
      queue.offer(handle);
    }
    public Envelope dequeue() { return queue.poll(); }
    public int numberOfMessages() { return queue.size(); }
    public boolean hasMessages() { return !queue.isEmpty(); }
    public void cleanUp(ActorRef owner, MessageQueue deadLetters) {
      for (Envelope handle: queue) {
        deadLetters.enqueue(owner, handle);
      }
    }
  }

  // This constructor signature must exist, it will be called by Akka
  public MyUnboundedMailbox(ActorSystem.Settings settings, Config config) {
    // put your initialization code here
  }

  // The create method is called to create the MessageQueue
  public MessageQueue create(Option<ActorRef> owner, Option<ActorSystem> system) {
    return new MyMessageQueue();
  }
}

doc

• Actors and Green Threads in Java Demystified
• Mailboxes
• Mailbox.scala