Java栅栏应用

栅栏分两类

CyclicBarrier

干什么用的

线程到达栅栏的位置时调用await方法，该线程会被阻塞，直到所有线程都到达栅栏位置。
当所有线程都到达栅栏位置，那么栅栏将打开，此时所有线程都被释放，栅栏将被重置以便下次使用。

栗子

一家人去吃肯德基，当大家都到齐了进行点名，一起进入。

package test;

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

class Solver {

    CyclicBarrier barrier;

    class Worker implements Runnable {

        private String name;

        public Worker(String name) {
            this.name = name;
        }

        public void run() {
            try {
                int await = barrier.await();
                System.out.println("" + name + "第" + await + "个到达门口");
            } catch (InterruptedException ex) {
                return;
            } catch (BrokenBarrierException ex) {
                return;
            }
        }
    }

    public void eatKFC(int numbers) throws InterruptedException {

        Runnable barrierAction = new Runnable() {
            public void run() {
                System.out.println("都到齐了，看看谁先到的");
            }
        };
        barrier = new CyclicBarrier(numbers, barrierAction);
        new Thread(new Worker("你二叔")).start();
        new Thread(new Worker("你大舅")).start();
        new Thread(new Worker("你七大爷")).start();
        new Thread(new Worker("你五叔")).start();
    }

    public static void main(String[] args) {
        Solver solver = new Solver();
        try {
            solver.eatKFC(4);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
}

Exchanger

干什么用的

栅栏的第二种形式
用于交换数据，A线程中的a数据，想和B线程中的b数据交换，当调用exchange时，会实现数据交换

栗子

一个班级的小A想和同一班级的小B换座位

package test;

import java.util.concurrent.Exchanger;

class FillAndEmpty {
    Exchanger exchanger = new Exchanger();
    Student student1 = new Student("xieyaoyan", 1);
    Student student2 = new Student("yingyinglei", 2);

    class FillingLoop implements Runnable {

        public void run() {
            try {
                System.out.println(student1.getName() + " 收拾书包，走向另一个座位");
                student1 = exchanger.exchange(student1);
                System.out.println("换完座位了，当前座位是： " + student1);
            } catch (InterruptedException ex) {
                System.out.println("FillingLoop.run");
            }
        }
    }

    class EmptyingLoop implements Runnable {

        public void run() {
            try {
                System.out.println(student2.getName() + " 收拾书包，走向另一个座位");
                student2 = exchanger.exchange(student2);
                System.out.println("换完座位了，当前座位是： = " + student2);
            } catch (InterruptedException ex) {
                System.out.println("EmptyingLoop.run");
            }
        }
    }

    void start() {
        new Thread(new FillingLoop()).start();
        new Thread(new EmptyingLoop()).start();
    }

    public static void main(String[] args) {
        FillAndEmpty fillAndEmpty = new FillAndEmpty();
        fillAndEmpty.start();
    }
}

class Student {
    private String name;
    private int id;

    public Student() {
    }

    public Student(String name, int id) {
        this.name = name;
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    @Override
    public String toString() {
        return "Student{" + "name='" + name + '\'' + ", id=" + id + '}';
    }
}