J.U.C知识点梳理

[TOC]

java.util.concurrent : 提供了并发编程的解决方案

1. CAS 是java.util.concurrent.atomic包的基础
2. AQS是java.util.concurrent.locks包以及一些常用类，比如：Semophore ，ReentrantLock等类的基础

J.U.C包的分类

1. 线程执行器executor
2. 锁locks
3. 原子变量类atomic
4. 并发工具类 tools
5. 并发集合collections

并发工具类

1. 闭锁 CountDownLatch
2. 栅栏 CyclicBarrier
3. 信号量Semaphore
4. 交换器 Exchanger

public class CountDownLatchDemo {
    public static void main(String[] args) throws InterruptedException {
        new CountDownLatchDemo().go();
    }
    private void go() throws InterruptedException {
        CountDownLatch countDownLatch = new CountDownLatch(3);
        // 依次创建3个线程,并启动
        new Thread(new Task(countDownLatch), "Thread1").start();
        Thread.sleep(1000);
        new Thread(new Task(countDownLatch), "Thread2").start();
        Thread.sleep(1000);
        new Thread(new Task(countDownLatch), "Thread3").start();
        countDownLatch.await();
        System.out.println("所有线程已到达,主线程开始执行" + System.currentTimeMillis());
    }
    class Task implements Runnable {
        private CountDownLatch countDownLatch;
        public Task(CountDownLatch countDownLatch) {
            this.countDownLatch = countDownLatch;
        }
        @Override
        public void run() {
            System.out.println("线程" + Thread.currentThread().getName() + "已经到达" + System.currentTimeMillis());
            countDownLatch.countDown();
        }
    }
}

　　

public class CyclicBarrierDemo {
    public static void main(String[] args) throws InterruptedException {
        new CyclicBarrierDemo().go();
    }
    private void go() throws InterruptedException {
        // 初始化栅栏的参与者数为3
        CyclicBarrier cyclicBarrier = new CyclicBarrier(3);
        // 依次创建3个线程,并启动
        new Thread(new Task(cyclicBarrier), "Thread1").start();
        Thread.sleep(1000);
        new Thread(new Task(cyclicBarrier), "Thread2").start();
        Thread.sleep(1000);
        new Thread(new Task(cyclicBarrier), "Thread3").start();
        Thread.sleep(1000);
        System.out.println("main");
    }
    class Task implements Runnable {
        private CyclicBarrier cyclicBarrier;
        public Task(CyclicBarrier cyclicBarrier) {
            this.cyclicBarrier = cyclicBarrier;
        }
        @Override
        public void run() {
            System.out.println("线程" + Thread.currentThread().getName() + "已经到达" + System.currentTimeMillis());
            try {
                cyclicBarrier.await();
            } catch (InterruptedException e) {
                e.printStackTrace();
            } catch (BrokenBarrierException e) {
                e.printStackTrace();
            }
            System.out.println("线程" + Thread.currentThread().getName() + "开始处理" + System.currentTimeMillis());
        }
    }
}

　　

public class SemaphoreDemo {
    public static void main(String[] args) {
        // 线程池
        ExecutorService exec = Executors.newCachedThreadPool();
        // 只能5个线程同时访问
        final Semaphore semp = new Semaphore(5);
        // 模拟20个客户端访问
        for (int index = 0; index < 20; index++) {
            final int NO = index;
            Runnable run = new Runnable() {
                public void run() {
                    try {
                        // 获取许可
                        semp.acquire();
                        System.out.println("Accessing: " + NO);
                        Thread.sleep((long) (Math.random() * 10000));
                        // 访问完后，释放
                        semp.release();
                    } catch (InterruptedException e) {
                    }
                }
            };
            exec.execute(run);
        }
        // 退出线程池
        exec.shutdown();
    }
}

　　

public class ExchangerDemo {
    private static Exchanger<String> exchanger = new Exchanger();
 
    public static void main(String[] args) {
 
        //代表男生和女生
        ExecutorService service = Executors.newFixedThreadPool(2);
 
        service.execute(() -> {
            try {
                //男生对女生说的话
                String girl = exchanger.exchange("我其实暗恋你很久了......");
                System.out.println("女生说：" + girl);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        });
        service.execute(() -> {
            try {
                System.out.println("女生慢慢的从教室里走出来......");
                TimeUnit.SECONDS.sleep(3);
                //男生对女生说的话
                String boy = exchanger.exchange("我很喜欢你......");
                System.out.println("男生说：" + boy);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        });

　　

主要用于生产者-消费者模式，在多线程场景时生产者线程在队列尾部添加元素，而消费者线程则在队列头部消费元素，通过这种方式能够达到将任务的生产和消费进行隔离的目的。

注意:BlockingQueue的加入方法，offer(),add(),put()