多线程--屏障的使用案例

import java.util.concurrent.BrokenBarrierException;
import java.util.concurrent.CyclicBarrier;


public class CyclicBarrierLearn {

    public static void main(String[] args) {
        
        final float x = 0.2f;
        
        int numberOfTerms = 10;
        
        final float[] arr = new float[numberOfTerms];
        
        //一旦barrier获得CPU，必须等到该线程执行完毕，否则CPU不会被释放，之所以出现这中情况
        //是因为barrierAction这个以一种回调接口的形式暴漏出来，其实底层的实现机制已经通过模板指定好了规则，当执行该方法之后
        //才统一唤醒与之相关的全部线程
        CyclicBarrier barrier = new CyclicBarrier(numberOfTerms, new Runnable() {
            
            @Override
            public void run() {
                float sum = 0;
                for (int i = 0; i < arr.length; i++) {
                    sum += arr[i];
                }
                System.out.println("ln (1 - " + x + ") ≈ " + -sum);
            }
        });
        
        for (int i = 0; i < numberOfTerms; i++) {
            new Thread(new TermCacl(barrier, i, x, arr)).start();
        }
        
    }
    
}


class TermCacl implements Runnable {
    
    private int termIndex;
    
    private CyclicBarrier barrier;
    
    private float x;
    
    private float[] arr;
    
    public TermCacl(CyclicBarrier barrier, int termIndex, float x, float[] arr) {
        this.barrier = barrier;
        this.termIndex = termIndex;
        this.x = x;
        this.arr = arr;
    }
    
    @Override
    public void run() {
        try {
            arr[termIndex] =  (float) (Math.pow(x, termIndex + 1) / (termIndex + 1));
            barrier.await();
            System.out.println(Thread.currentThread().getName() + termIndex);
        } catch (InterruptedException e) {
            e.printStackTrace();
        } catch (BrokenBarrierException e) {
            e.printStackTrace();
        }
    }
}