package com.ccfdod.juc;

 import java.util.concurrent.locks.Condition;

 import java.util.concurrent.locks.Lock;

 import java.util.concurrent.locks.ReentrantLock;

 /**

 * 题目：编写一个程序，开启 3 个线程，这三个线程的 ID 分别为 A、B、C，每个线程将自己的 ID 在屏幕上打印 10 遍，要求输出的结果必须按顺序显示。

 * 如：ABCABCABC……

 */

 class AlternateDemo {

     //标志当前由哪一个线程输出，1代表A，2代表B，3代表C

     private int number = 1;

     Lock lock = new ReentrantLock();

     //Condition的强大之处在于它可以为多个线程间建立不同的Condition

     Condition condition1 = lock.newCondition();

     Condition condition2 = lock.newCondition();

     Condition condition3 = lock.newCondition();

     // loopNum:当前循环轮数

     public void loopA(int loopNum) {

         //上锁

         lock.lock();

         try {

             while (number != 1) {

                 //等待

                 condition1.await();

             }

             System.out.println(Thread.currentThread().getName() + ", currentLoopNum is " + loopNum);

             number = 2;

             //唤醒

             condition2.signal();

         } catch (InterruptedException e) {

             e.printStackTrace();

         } finally {

             //确保释放锁

             lock.unlock();

         }

     }

     public void loopB(int loopNum) {

         lock.lock();

         try {

             while (number != 2) {

                 condition2.await();

             }

             System.out.println(Thread.currentThread().getName() + ", currentLoopNum is " + loopNum);

             number = 3;

             condition3.signal();

         } catch (InterruptedException e) {

             e.printStackTrace();

         } finally {

             lock.unlock();

         }

     }

     public void loopC(int loopNum) {

         lock.lock();

         try {

             while (number != 3) {

                 condition3.await();

             }

             System.out.println(Thread.currentThread().getName() + ", currentLoopNum is " + loopNum);

             number = 1;

             condition1.signal();

         } catch (InterruptedException e) {

             e.printStackTrace();

         } finally {

             lock.unlock();

         }

     }

 }

 public class TestABCAlternate {

     public static void main(String[] args) {

         AlternateDemo ad = new AlternateDemo();

         new Thread(new Runnable() {

             @Override

             public void run() {

                 for (int i = 0; i < 10; i++)

                     ad.loopA(i);

             }

         }, "A").start();

         new Thread(new Runnable() {

             @Override

             public void run() {

                 for (int i = 0; i < 10; i++)

                     ad.loopB(i);

             }

         }, "B").start();

         new Thread(new Runnable() {

             @Override

             public void run() {

                 for (int i = 0; i < 10; i++)

                     ad.loopC(i);

             }

         }, "C").start();

     }

 }