多线程进阶JUC之阻塞队列与同步队列

阻塞队列

使用场景：多线程并发处理和线程池
四组API

1. 抛出异常
2. 不会抛出异常
3. 阻塞 等待
4. 超时等待

/**
 * @Author Weton Li
 * @Date 2021/2/10 20:49
 */
public class BlockingQueueTest {
    
    
    public static void main(String[] args) throws InterruptedException {
    
    
//        test1();
//        test2();
//        test3();
        test4();

    }

    /**
     * 抛出异常
     *
     * @throws InterruptedException
     */
    public static void test1() throws InterruptedException {
    
    
        // 队列容量为3

        ArrayBlockingQueue arrayBlockingQueue = new ArrayBlockingQueue<>(3); // 队列容量

        System.out.println(arrayBlockingQueue.add("a"));
        System.out.println(arrayBlockingQueue.add("b"));
        System.out.println(arrayBlockingQueue.add("c"));
//        System.out.println(arrayBlockingQueue.add("d")); 报IllegalStateException异常，之前是报oncurrentModificationException

        System.out.println(arrayBlockingQueue.remove()); // a
        System.out.println(arrayBlockingQueue.remove()); // b
        System.out.println("队首为：" + arrayBlockingQueue.element()); // 检测队首元素，当无队首时，报异常
        System.out.println(arrayBlockingQueue.remove()); // c
//        System.out.println(arrayBlockingQueue.remove()); // 报NoSuchElementException异常
    }

    /**
     * 有返回值，不抛异常
     *
     * @throws InterruptedException
     */
    public static void test2() throws InterruptedException {
    
    
        // 队列容量为3
        ArrayBlockingQueue arrayBlockingQueue = new ArrayBlockingQueue<>(3);

        System.out.println(arrayBlockingQueue.offer("a"));
        System.out.println(arrayBlockingQueue.offer("b"));
        System.out.println(arrayBlockingQueue.offer("c"));
        System.out.println(arrayBlockingQueue.offer("d")); // false，不报异常

        System.out.println(arrayBlockingQueue.poll());
        System.out.println(arrayBlockingQueue.poll());
        System.out.println(arrayBlockingQueue.poll());
        System.out.println(arrayBlockingQueue.poll()); // null，不报异常
        System.out.println("队首为：" + arrayBlockingQueue.peek()); // 队首为null，永不报异常
    }

    /**
     * 等待，阻塞（一直阻塞）
     */
    public static void test3() throws InterruptedException {
    
    
        ArrayBlockingQueue arrayBlockingQueue = new ArrayBlockingQueue<>(3);
        arrayBlockingQueue.put("a");
        arrayBlockingQueue.put("b");
        arrayBlockingQueue.put("c");
//        arrayBlockingQueue.put("d"); // 不报错抛异常，会永远阻塞

        System.out.println(arrayBlockingQueue.take());
        System.out.println(arrayBlockingQueue.take());
        System.out.println(arrayBlockingQueue.take());
//        System.out.println(arrayBlockingQueue.take()); // 不报错抛异常，会永远阻塞
    }

    /**
     * 等待，阻塞（等待超时）
     */
    public static void test4() throws InterruptedException {
    
    
        ArrayBlockingQueue arrayBlockingQueue = new ArrayBlockingQueue<>(3);
        arrayBlockingQueue.offer("a");
        arrayBlockingQueue.offer("b");
        arrayBlockingQueue.offer("c");
        arrayBlockingQueue.offer("d", 2, TimeUnit.SECONDS); // 因为队列容量为3，故等两秒

        System.out.println(arrayBlockingQueue.poll());
        System.out.println(arrayBlockingQueue.poll());
        System.out.println(arrayBlockingQueue.poll());
        arrayBlockingQueue.poll(2,TimeUnit.SECONDS); // 因队列容量为3，故等两秒自动退出
    }
}

SynchronousQueue同步队列(容量唯一）特殊的阻塞队列

/**
 * 放一个取一个
 * 只有一个停车位，停一个开走后第二辆车才能停进来。
 * 茵上厕所锁门，彤在外等待。安全。
 * @Author Weton Li
 * @Date 2021/2/10 22:52
 */
public class SynchronousQueueTest {
    
    
    public static void main(String[] args) {
    
    

        SynchronousQueue<String> synchronousQueue = new SynchronousQueue(); // 默认且只能为1

        new Thread(()->{
    
    
            try {
    
    
//                System.out.println(Thread.currentThread().getName()+"put a");
                synchronousQueue.put("a");
//                System.out.println(Thread.currentThread().getName()+"put b");
                synchronousQueue.put("b");
//                System.out.println(Thread.currentThread().getName()+"put c");
                synchronousQueue.put("c");
            } catch (InterruptedException e) {
    
    
                e.printStackTrace();
            }
        },"T1").start();

        new Thread(()->{
    
    
            try {
    
    
                TimeUnit.SECONDS.sleep(2);
                System.out.println(Thread.currentThread().getName()+"=>"+synchronousQueue.take());
                TimeUnit.SECONDS.sleep(2);
                System.out.println(Thread.currentThread().getName()+"=>"+synchronousQueue.take());
                TimeUnit.SECONDS.sleep(2);
                System.out.println(Thread.currentThread().getName()+"=>"+synchronousQueue.take());

            } catch (InterruptedException e) {
    
    
                e.printStackTrace();
            }
        },"T2").start();
    }
}