使用LinkedList實現安全佇列

         使用 wait notify 實現一個佇列，佇列有2個方法，add 和 get 。add方法往佇列中新增元素，get方法往佇列中獲得元素。佇列必須是執行緒安全的。如果get執行時，佇列為空，執行緒必須阻塞等待，直到有佇列有資料。如果add時，佇列已經滿，則add執行緒要等待，直到佇列有空閒空間。 

        

/**
 * 使用LinkedList實現安全佇列
 *
 */
public class SafeLinkedList<E> {


    private LinkedList<E> data = new LinkedList<>();
    private int totalSize;

    public SafeLinkedList(int totalSize) {
        this.totalSize = totalSize;

    }

    /**
     * 當佇列已滿時候，阻塞，直到取走資料為止
     * @param e
     */
    public void add(E e) {
        synchronized (data) {
            if (data.size() == totalSize) {
                try {
                    data.wait();
                } catch (InterruptedException e1) {
                    Thread.interrupted();
                    data.notifyAll();
                    System.out.println("佇列已滿啦！");
                }

            }
            data.add(e);
            data.notifyAll();

        }

    }

    /**
     * 當佇列為空時候，阻塞等待
     * @return
     */
    public E get() {
        synchronized (data) {

            if (data.isEmpty()) {
                try {
                    data.wait();
                } catch (InterruptedException e) {
                    Thread.interrupted();
                    data.notifyAll();
                }
            }

            E e = data.getFirst();//獲取佇列頭元素
            data.removeFirst();//移除對頭元素
            data.notifyAll();
            return e;
        }
    }

    public synchronized int size() {
        return data.size();
    }
}

測試佇列：

/**
 * 多執行緒條件下測試LinkedList存取資料是否安全
 */
public class SafeLinkedListTest {

    private SafeLinkedList<String> data = new SafeLinkedList<>(10);

    @Test
    public void putGetTest() throws InterruptedException {

        //add test
        Thread t1 = new Thread(new OperAddThread());
        Thread t2 = new Thread(new OperAddThread());
        Thread t3 = new Thread(new OperAddThread());

        Thread getThread = new Thread(new OperGetThread());
        getThread.setName("getThread");

        t1.start();
        t2.start();
        t3.start();
        getThread.start();

        t1.join();
        t2.join();
        t3.join();
        getThread.join();

        System.out.println(data.size());

    }


    class OperAddThread implements Runnable {

        @Override
        public void run() {
            for (int i = 0; i < 4; i++) {
                String addData=Thread.currentThread().getName()+"|"+String.valueOf(i);
                data.add(addData);
                System.out.println("add size=" + data.size());
                System.out.println(Thread.currentThread().getName() + " addData=" + addData);
            }
        }
    }

    class OperGetThread implements Runnable {
        @Override
        public void run() {
            int i=11;
            while (i>=0) {
                i--;
                String value = data.get();
                System.out.println("get size=" + data.size());
                System.out.println("get string--" + " ;value=" + value);
            }
        }
    }
}