package com.jiucaiyuan.net.thread;



import java.util.concurrent.locks.Condition;

import java.util.concurrent.locks.ReentrantLock;



/**

 * <p>

 * 题目：

 * 编写程序，开启三个线程，这三个线程的ID分别是A，B，C，每个线程将自己的ID在屏幕上打印十次，

 * 要求输出结果必须按照ABC的顺序显示，如：ABCABCABC...

 *

 * 指定线程唤醒轮循打印,使用ReentrantLock和Condition。 本方法空间开销较大，因为使用了三个条件对象，

 * 但是本方法是定点唤醒线程，并不会产生额外的上下文切换开销。总体来说，本方法性能更优。

 *

 * </p>

 */

class RotationPrint implements Runnable {

    private static volatile String whoCanPrint;

    private String whoPrintFollow;

    private int printTime;

    private ReentrantLock reentrantLock;

    private Condition myCondition;

    private Condition nextCondition;



    public RotationPrint(ReentrantLock lock, Condition myCondition, Condition nextCondition, String nextName) {

        this.printTime = 0;

        this.reentrantLock = lock;

        this.myCondition = myCondition;

        this.nextCondition = nextCondition;

        this.whoPrintFollow = nextName;

    }



    public static void setWhoCanPrint(String s) {

        whoCanPrint = s;

    }



    @Override

    public void run() {

        while (printTime++ < 10) {

            try {

                reentrantLock.lock();

                //判断当前线程是否是需要打印的线程。

                while (Thread.currentThread().getName() != whoCanPrint) {

                    try {

                        myCondition.await();

                    } catch (InterruptedException e) {

                        e.printStackTrace();

                    }

                }

                //System.out.println("线程" + Thread.currentThread().getName() + "   第" + printTimes + "次打印");

                System.out.print(Thread.currentThread().getName());

                whoCanPrint = whoPrintFollow;

                //指定唤醒下一个需要打印的线程。

                nextCondition.signal();

            } finally {

                reentrantLock.unlock();

            }

        }    



    }

    public static void main(String[] args) {

        ReentrantLock lock = new ReentrantLock();

        Condition aCondition = lock.newCondition();

        Condition bCondition = lock.newCondition();

        Condition cCondition = lock.newCondition();

        //设置第一个需要打印的线程

        RotationPrint.setWhoCanPrint("A");

        new Thread(new RotationPrint(lock, aCondition, bCondition, "B"), "A").start();

        new Thread(new RotationPrint(lock, bCondition, cCondition, "C"), "B").start();

        new Thread(new RotationPrint(lock, cCondition, aCondition, "A"), "C").start();

    }

}