JUC之线程协作工具

CountDownLatch倒数门闩

流程：倒数结束之前一直处于等待状态，直到倒数结束时，此线程才开始工作。

主要方法：

//构造方法传入倒数次数
 public CountDownLatch(int count) {
        if (count < 0) throw new IllegalArgumentException("count < 0");
        this.sync = new Sync(count);
    }



public void countDown() {
        sync.releaseShared(1);
    }



public void await() throws InterruptedException {
        sync.acquireSharedInterruptibly(1);
    }

 使用场景：

• 一个线程等待多个线程执行完毕，再继续自己的工作。一等多
• 多个线程等待同一个信号。多等一

代码示例

/**
 * 描述：     模拟100米跑步，5名选手都准备好了，只等裁判员一声令下，所有人同时开始跑步。当所有人都到终点后，比赛结束。
 */
public class CountDownLatchDemo1And2 {

    public static void main(String[] args) throws InterruptedException {
        CountDownLatch begin = new CountDownLatch(1);

        CountDownLatch end = new CountDownLatch(5);
        ExecutorService service = Executors.newFixedThreadPool(5);
        for (int i = 0; i < 5; i++) {
            final int no = i + 1;
            Runnable runnable = new Runnable() {
                @Override
                public void run() {
                    System.out.println("No." + no + "准备完毕，等待发令枪");
                    try {
                        begin.await();
                        System.out.println("No." + no + "开始跑步了");
                        Thread.sleep((long) (Math.random() * 10000));
                        System.out.println("No." + no + "跑到终点了");
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    } finally {
                        end.countDown();
                    }
                }
            };
            service.submit(runnable);
        }
        //裁判员检查发令枪...
        Thread.sleep(5000);
        System.out.println("发令枪响，比赛开始！");
        begin.countDown();

        end.await();
        System.out.println("所有人到达终点，比赛结束");
    }
}

Semaphore信号量

使用场景：用来限制或者管理资源有限的使用情况。作用是维护一个许可证的计数，当信号量拥有的许可证为0时，那么下一个线程就需要等待直到有线程释放许可证。

代码示例

/**
 * 描述：     演示Semaphore用法
 */
public class SemaphoreDemo {

    static Semaphore semaphore = new Semaphore(5, true);

    public static void main(String[] args) {
        ExecutorService service = Executors.newFixedThreadPool(50);
        for (int i = 0; i < 100; i++) {
            service.submit(new Task());
        }
        service.shutdown();
    }

    static class Task implements Runnable {

        @Override
        public void run() {
            try {
                semaphore.acquire(3);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            System.out.println(Thread.currentThread().getName() + "拿到了许可证");
            try {
                Thread.sleep(2000);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            System.out.println(Thread.currentThread().getName() + "释放了许可证");
            semaphore.release(2);
        }
    }
}

 Condition

代码示例：

/**
 * 描述：     演示用Condition实现生产者消费者模式
 */
public class ConditionDemo2 {

    private int queueSize = 10;
    private PriorityQueue<Integer> queue = new PriorityQueue<Integer>(queueSize);
    private Lock lock = new ReentrantLock();
    private Condition notFull = lock.newCondition();
    private Condition notEmpty = lock.newCondition();

    public static void main(String[] args) {
        ConditionDemo2 conditionDemo2 = new ConditionDemo2();
        Producer producer = conditionDemo2.new Producer();
        Consumer consumer = conditionDemo2.new Consumer();
        producer.start();
        consumer.start();
    }

    class Consumer extends Thread {

        @Override
        public void run() {
            consume();
        }

        private void consume() {
            while (true) {
                lock.lock();
                try {
                    while (queue.size() == 0) {
                        System.out.println("队列空，等待数据");
                        try {
                            notEmpty.await();
                        } catch (InterruptedException e) {
                            e.printStackTrace();
                        }
                    }
                    queue.poll();
                    notFull.signalAll();
                    System.out.println("从队列里取走了一个数据，队列剩余" + queue.size() + "个元素");
                } finally {
                    lock.unlock();
                }
            }
        }
    }

    class Producer extends Thread {

        @Override
        public void run() {
            produce();
        }

        private void produce() {
            while (true) {
                lock.lock();
                try {
                    while (queue.size() == queueSize) {
                        System.out.println("队列满，等待有空余");
                        try {
                            notFull.await();
                        } catch (InterruptedException e) {
                            e.printStackTrace();
                        }
                    }
                    queue.offer(1);
                    notEmpty.signalAll();
                    System.out.println("向队列插入了一个元素，队列剩余空间" + (queueSize - queue.size()));
                } finally {
                    lock.unlock();
                }
            }
        }
    }

}

CyclicBarrier循环栅栏

代码示例：

/**
 * 描述：    演示CyclicBarrier
 */
public class CyclicBarrierDemo {
    public static void main(String[] args) {
        CyclicBarrier cyclicBarrier = new CyclicBarrier(5, new Runnable() {
            @Override
            public void run() {
                System.out.println("所有人都到场了， 大家统一出发！");
            }
        });
        for (int i = 0; i < 10; i++) {
            new Thread(new Task(i, cyclicBarrier)).start();
        }
    }

    static class Task implements Runnable{
        private int id;
        private CyclicBarrier cyclicBarrier;

        public Task(int id, CyclicBarrier cyclicBarrier) {
            this.id = id;
            this.cyclicBarrier = cyclicBarrier;
        }

        @Override
        public void run() {
            System.out.println("线程" + id + "现在前往集合地点");
            try {
                Thread.sleep((long) (Math.random()*10000));
                System.out.println("线程"+id+"到了集合地点，开始等待其他人到达");
                cyclicBarrier.await();
                System.out.println("线程"+id+"出发了");
            } catch (InterruptedException e) {
                e.printStackTrace();
            } catch (BrokenBarrierException e) {
                e.printStackTrace();
            }
        }
    }
}

 与CountDownLatch的区别？