Java并发学习笔记(八)-LinkedBlockingQueue

LinkedBlockingQueue是由链表组成的阻塞队列，先来看demo

public class LinkedBlockingQueueDemo {

	public static void main(String[] args) {
		ExecutorService es = Executors.newCachedThreadPool();
		BlockingQueue<Bread> queue = new LinkedBlockingQueue<Bread>(10);
		for(int i = 0; i < 2; i++){
			es.execute(new Baker(queue));
		}
		
		for(int i = 0; i < 10; i++){
			es.execute(new BreadConsumer(queue));
		}
		es.shutdown();
	}

}

class Baker implements Runnable{
	private static int no = 0;
	private int id = ++no;
	private int count = 0;
	
	private BlockingQueue<Bread> queue;
	
	public Baker(BlockingQueue<Bread> queue){
		this.queue = queue;
	}

	@Override
	public void run() {
		for(int i = 0; i < 10; i++){
			System.out.println("面包师" + id + "正准备做第" + ++count + "面包");
			Bread bread = new Bread();
//			满队列情况下，阻塞
			try {
				queue.put(bread);
				System.out.println("面包师" + id + "做的第" + count + "面包是面包"+ bread.getId());
			} catch (InterruptedException e) {
					
			}
		}	
	}
}

class BreadConsumer implements Runnable{
	private static int no = 0;
	private int id = ++no;
	private int count = 0;
	
	private BlockingQueue<Bread> queue;
	
	public BreadConsumer(BlockingQueue<Bread> queue){
		this.queue = queue;
	}
	
	@Override
	public void run() {
		for(int i = 0; i < 2; i++){
			System.out.println("顾客 " + id + "准备买第" + ++count +"个面包" );
			Bread bread = null;
//		空队列情况下，阻塞
			try {
				bread = queue.take();
			} catch (InterruptedException e) {
				
			}
		<span style="white-space:pre">	</span>System.out.println("顾客" + id + "买到的第" +count+"个面包是面包" + bread.getId());
		}
	}
	
}

class Bread {
	private static int count = 0;
	private int id = ++count;
	public int getId() {
		return id;
	}
}

默认情况下，其容量为Integer.MAX_VALUE

    public LinkedBlockingQueue() {
        this(Integer.MAX_VALUE);
    }

    public LinkedBlockingQueue(int capacity) {
        if (capacity <= 0) throw new IllegalArgumentException();
        this.capacity = capacity;
        last = head = new Node<E>(null);
    }

    /** 链表头 */
    private transient Node<E> head;

    /** 链表尾 */
    private transient Node<E> last;

    /** 出队的锁 */
    private final ReentrantLock takeLock = new ReentrantLock();

    /** Wait queue for waiting takes */
    private final Condition notEmpty = takeLock.newCondition();

    /** 入队的锁 */
    private final ReentrantLock putLock = new ReentrantLock();

    /** Wait queue for waiting puts */
    private final Condition notFull = putLock.newCondition();

    public void put(E e) throws InterruptedException {
        if (e == null) throw new NullPointerException();
        int c = -1;
        final ReentrantLock putLock = this.putLock;
        final AtomicInteger count = this.count;
        putLock.lockInterruptibly();
        try {
            while (count.get() == capacity) { 
                    notFull.await();
            }
            enqueue(e);
            c = count.getAndIncrement();
            if (c + 1 < capacity)
                notFull.signal();
        } finally {
            putLock.unlock();
        }
        if (c == 0)
            signalNotEmpty();
    }

队列里，插入元素，会插入队尾

    private void enqueue(E x) {
        // assert putLock.isHeldByCurrentThread();
        last = last.next = new Node<E>(x);
    }

    public E take() throws InterruptedException {
        E x;
        int c = -1;
        final AtomicInteger count = this.count;
        final ReentrantLock takeLock = this.takeLock;
        takeLock.lockInterruptibly();
        try {
                while (count.get() == 0) {
                    notEmpty.await();
                }
            x = dequeue();
            c = count.getAndDecrement();
            if (c > 1)
                notEmpty.signal();
        } finally {
            takeLock.unlock();
        }
        if (c == capacity)
            signalNotFull();
        return x;
    }

    private E dequeue() {
        // assert takeLock.isHeldByCurrentThread();
        Node<E> h = head;
        Node<E> first = h.next;
        h.next = h; // help GC
        head = first;
        E x = first.item;
        first.item = null;
        return x;
    }