java多线程之Phaser

Phaser表示阶段同步器，用来解决控制多个线程分阶段共同完成任务的情景问题。我们可以将其看成一个一个的阶段，每个阶段都有需要执行的线程任务，任务执行完毕就进入下一个阶段。所以Phaser特别适合使用在重复执行或者重用的情况。

一共五个人去爬山，先在山脚集合，再爬到山顶集合

package com.test.juc.lock;

import java.util.Random;
import java.util.concurrent.Phaser;
import java.util.concurrent.TimeUnit;

public class PhaserTest {

    static ClimbingPhaser cp = new ClimbingPhaser();

    public static void main(String[] args) {
        cp.bulkRegister(5);
        for(int i = 0; i < 5; i++) {
            new Thread(() -> {
                Person p = new Person(Thread.currentThread().getName());
                p.begin();
                cp.arriveAndAwaitAdvance();
                p.climbing();
                cp.arriveAndAwaitAdvance();
            }).start();
        }
    }

    static class ClimbingPhaser extends Phaser {

        @Override
        protected boolean onAdvance(int phase, int registeredParties) {
            switch (phase) {
                case 0:
                    System.out.println("所有人到达山脚");
                    return false;
                case 1:
                    System.out.println("山顶集合完毕");
                    return true;
                default:
                    return true;
            }
        }
    }

    static void milliSleep(int milli) {
        try {
            TimeUnit.MILLISECONDS.sleep(milli);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }

    static class Person {
        String name;

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

        void begin() {
            milliSleep(new Random().nextInt(1000));
            System.out.println(name + "到达山脚");
        }

        void climbing() {
            milliSleep(new Random().nextInt(1000));
            System.out.println(name + "爬上山顶");
        }
    }
}

执行结果
Thread-0到达山脚
Thread-1到达山脚
Thread-4到达山脚
Thread-3到达山脚
Thread-2到达山脚
所有人到达山脚
Thread-1爬上山顶
Thread-2爬上山顶
Thread-3爬上山顶
Thread-4爬上山顶
Thread-0爬上山顶
山顶集合完毕