篱栅：CyclicBarrier

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CountDownLatch的计数器只能使用一次，而CyclicBarrier【塞克丽克百瑞尔】的计数器可以使用reset()方法重置。所以CyclicBarrier能处理更为复杂的业务场景。例如，如果计算发生错误，可以重置计数器，并让线程重新执行一次。
CyclicBarrier还提供其他有用的方法，比如getNumberWaiting方法可以获得Cyclic-Barrier阻塞的线程数量。isBroken()方法用来了解阻塞的线程是否被中断（thread.interrupt()）。

package mytest;import java.util.Map.Entry;import java.util.concurrent.BrokenBarrierException;import java.util.concurrent.ConcurrentHashMap;import java.util.concurrent.CyclicBarrier;import java.util.concurrent.ExecutorService;import java.util.concurrent.Executors;public class CyclicbarrierTest implements Runnable {    private static final int THREAD_COUNT = 4;    private CyclicBarrier cyclicBarrier = new CyclicBarrier(THREAD_COUNT, this);//    private static ExecutorService threadPool = Executors.newFixedThreadPool(THREAD_COUNT);    private ConcurrentHashMap<String, Integer> sheetBankWaterCount = new ConcurrentHashMap<String, Integer>();    private void count() {        for (int i = 0; i < THREAD_COUNT; i++) {            //线程池一跑起来，就停不下来了            threadPool.execute(new Runnable() {                @Override                public void run() {                    sheetBankWaterCount.put(Thread.currentThread().getName(), 1);                    try {                        cyclicBarrier.await();                    } catch (InterruptedException e) {                        e.printStackTrace();                    } catch (BrokenBarrierException e) {                        e.printStackTrace();                    }                    System.out.println("===");                }            });        }    }    @Override    public void run() {        int result = 0;        for (Entry<String, Integer> sheet : sheetBankWaterCount.entrySet()) {            result += sheet.getValue();        }        sheetBankWaterCount.put("result", result);        System.out.println(result);        try {            Thread.sleep(10 * 1000);        } catch (InterruptedException e) {            e.printStackTrace();        }    }    public static void main(String[] args) {        CyclicbarrierTest ct = new CyclicbarrierTest();        ct.count();        System.out.println("over");    }}

执行结果：

over 主线程继续执行
4 this线程在await之后执行
pool-1-thread-2 over this线程执行完了，await后面的代码再执行
pool-1-thread-1 over
pool-1-thread-4 over
pool-1-thread-3 over

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