ReentrantLock、CountDownLatch、CyclicBarrier简介

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ReentrantLock、CountDownLatch、CyclicBarrier

1、ReentrantLock可重入互斥锁

公平锁与非公平锁的释放锁步骤是一致的。获取锁的过程不一致，非公平锁是让当前线程优先独占，而公平锁则是让等待时间最长的线程优先，非公平的可能让其他线程没机会执行，而公平的则可以让等待时间最长的先执行，但是性能上会差点。

2、CountDownLatch是一个线程（或者多个线程）等待（await）多个线程（countDown），当多个线程都countDown完，await线程继续往后执行。

3、CyclicBarrier是多个线程相互等待（await），当所有都await后一起继续往后执行。

ReentrantLock Demo

class ReentrantLockDemo {
  private final ReentrantLock lock = new ReentrantLock();

  public void m() {
    lock.lock();
    try {
      // ... method body
    } finally {
      lock.unlock()
    }
  }
}

CountDownLatch Demo

public class CountDownLatchDemo { 

    public static void main(String[] args){

        final CountDownLatch latch = new CountDownLatch(10);

        ThreadPoolExecutor executor = new ThreadPoolExecutor(5, 10, 200, TimeUnit.MILLISECONDS,
            new ArrayBlockingQueue<Runnable>(5));
        for(int i=0;i<10;i++){
            TestTask task=new TestTask("task_" + (i+1),latch);
            executor.execute(task);
        }

        try {
            System.out.println("等待10个子线程执行完毕...");
            latch.await();
            System.out.println("10个子线程已经执行完毕");
            System.out.println("继续执行主线程");
        }catch(Exception e){
            e.printStackTrace();
        }

        executor.shutdown();        
    }
}

class TestTask implements Runnable{

    private String name;

    private CountDownLatch latch;

    public TestTask(String name,CountDownLatch latch){
        this.name=name;
        this.latch=latch;
    }

    @Override
    public void run() {
        System.out.println(name + " start running.");
        try {
            Thread.sleep(2000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        System.out.println(name + " start end.");
        this.latch.countDown();
    }  
}

CyclicBarrier Demo

public class CyclicBarrierDemo { 
    public static void main(String[] args){
        CyclicBarrier barrier  = new CyclicBarrier(10);
        ThreadPoolExecutor executor = new ThreadPoolExecutor(10, 10, 200, TimeUnit.MILLISECONDS,
            new ArrayBlockingQueue<Runnable>(5));
        for(int i=0;i<10;i++){
            TestTask task=new TestTask("客人_" + (i+1),barrier,i);
            executor.execute(task);
        }       
    }
}

class TestTask implements Runnable{

    private String name;

    private CyclicBarrier barrier;

    private int index;

    public TestTask(String name,CyclicBarrier barrier,int index){
        this.name=name;
        this.barrier=barrier;
        this.index=index;
    }

    @Override
    public void run() {       
        try {
            Thread.sleep(1000 + this.index*1000);
            System.out.println(name + " 哥已到");
            Thread.sleep(1000 + this.index*2000);
            System.out.println(name + " 哥已就坐，其他几个哥赶快啊，哥饿啦.");
            this.barrier.await();
        } catch (Exception e) {
            e.printStackTrace();
        }
        System.out.println(name + "终于都到啦，开吃啦");

    }  
}