CyclicBarrier的作用是攔截多個(gè)線程，當(dāng)所有線程到達(dá)指定位置時(shí)，在開始往下面執(zhí)行，否則線程等待。
兩種構(gòu)造函數(shù)：

public CyclicBarrier(int parties)
public CyclicBarrier(int parties, Runnable barrierAction)

其中parties是線程個(gè)數(shù)，barrierAction是所有線程到達(dá)后執(zhí)行的任務(wù)。
多線程數(shù)組求和，首先對(duì)數(shù)組進(jìn)行分段，每段一個(gè)線程進(jìn)行求和，當(dāng)所有線程都完成計(jì)算后，在barrierAction中進(jìn)行整體求和。

public class CyclicBarrierTest implements Runnable {

    CyclicBarrierTest(int count) {
        this.count = count;
        cyclicBarrier = new CyclicBarrier(count, this);
        executorService = Executors.newFixedThreadPool(count);
    }

    private Map<String, Integer> sumMap = new HashMap<>();
    private int count = 4;
    private CyclicBarrier cyclicBarrier;
    private ExecutorService executorService;

    public void sum(int[] arr) {
        int size = arr.length;
        int batch = size / count + 1;
        for (int i = 0; i < count; i++) {
            int end;
            int start;
            start = i * batch;
            end = Math.min(start + batch, size);

            System.out.println(start + " " + end);
            executorService.execute(new Calculator(arr, start, end));
        }
        executorService.shutdown();
    }

    public static void main(String[] args) {

        int[] arr = new int[]{1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11};

        CyclicBarrierTest cyclicBarrierTest = new CyclicBarrierTest(5);
        cyclicBarrierTest.sum(arr);

    }

    class Calculator implements Runnable {

        private int[] arr;
        private int start;
        private int end;

        Calculator(int[] arr, int start, int end) {
            this.arr = arr;
            this.start = start;
            this.end = end;
        }

        @Override
        public void run() {
            int sum = 0;
            for (int i = start; i < end; i++) {
                sum += arr[i];
            }
            sumMap.put(Thread.currentThread().getName(), sum);
            try {
              //  線程等待，當(dāng)所有線程都到此處時(shí)在往下面執(zhí)行
                cyclicBarrier.await();
            } catch (InterruptedException | BrokenBarrierException e) {
                e.printStackTrace();
            }
        }
    }

    @Override
    public void run() {
        long sum = sumMap.values().stream().reduce(Integer::sum).get();
        System.out.println(sum);
    }
}