TransferQueue实例

序

本文主要简介一下TransferQueue。

TransferQueue

TransferQueue(java7引入)继承了BlockingQueue（BlockingQueue又继承了Queue）并扩展了一些新方法。生产者会一直阻塞直到所添加到队列的元素被某一个消费者所消费（不仅仅是添加到队列里就完事）。

LinkedTransferQueue

LinkedTransferQueue实际上是ConcurrentLinkedQueue、SynchronousQueue（公平模式）和LinkedBlockingQueue的超集。而且LinkedTransferQueue更好用，因为它不仅仅综合了这几个类的功能，同时也提供了更高效的实现。

对比SynchronousQueue

SynchronousQueue使用两个队列（一个用于正在等待的生产者、另一个用于正在等待的消费者）和一个用来保护两个队列的锁。而LinkedTransferQueue使用CAS操作实现一个非阻塞的方法，这是避免序列化处理任务的关键。

使用场景

当我们不想生产者过度生产消息时，TransferQueue可能非常有用，可避免发生OutOfMemory错误。在这样的设计中，消费者的消费能力将决定生产者产生消息的速度。

实例

public class LinkedTransferQueueDemo {
    static LinkedTransferQueue lnkTransQueue = new LinkedTransferQueue();
    public static void main(String[] args) {
        ExecutorService exService = Executors.newFixedThreadPool(2);
        Producer producer = new LinkedTransferQueueDemo().new Producer();
        Consumer consumer = new LinkedTransferQueueDemo().new Consumer();
        exService.execute(producer);
        exService.execute(consumer);
        exService.shutdown();
    }
    class Producer implements Runnable{
        @Override
        public void run() {
            for(int i=0;i<3;i++){
                try {
                    System.out.println("Producer is waiting to transfer...");
                    lnkTransQueue.transfer("A"+i);
                    System.out.println("producer transfered element: A"+i);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        }
    }
    class Consumer implements Runnable{
        @Override
        public void run() {
            for(int i=0;i<3;i++){
                try {
                    System.out.println("Consumer is waiting to take element...");
                    String s= lnkTransQueue.take();
                    System.out.println("Consumer received Element: "+s);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        }
    }
}

输出

Producer is waiting to transfer...
Consumer is waiting to take element...
producer transfered element: A0
Producer is waiting to transfer...
Consumer received Element: A0
Consumer is waiting to take element...
producer transfered element: A1
Producer is waiting to transfer...
Consumer received Element: A1
Consumer is waiting to take element...
Consumer received Element: A2
producer transfered element: A2

doc

• Java 7中的TransferQueue
• Guide to the Java TransferQueue
• TransferQueue and LinkedTransferQueue Java Example
• Java TransferQueue
• Fork/Join模式(JSR166y)手记之TransferQueue/LinkedTransferQueue
• 似懂非懂的SynchronousQueue和长度为1的BlockingQueue