黑马程序员—学习日志，多线程关于3个线程轮流执行的问题。

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看完多线程，毕老师讲到了2个线程之间轮流执行。但是怎么让3个多线程轮流执行呢？

下边让我们来分析一下代码。

JDK1.5中提供了多线程升级解决方案。

将同步synchronized替换成 实现LOCK操作

将Object 中的wait，notify，notifyAll，替换成Condition对象

该对象可以Lock锁，进行获取

该示例中实现了本方只唤醒对方的操作

import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;

public class Workkk {
public static void main(String[] args) {

final HomeWorkee h = new HomeWorkee();
new Thread() {
public void run() {
for (int i = 0; i < 3; i++)
try {
h.haha();
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}.start();

new Thread() {
public void run() {
for (int i = 0; i < 3; i++)
try {
h.hah();
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}.start();

new Thread() {
public void run() {
for (int i = 0; i < 3; i++)
try {
h.ha();
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}.start();
}

}

class HomeWorkee {
private int x = 1;
private int flag = 3; //标记为3，只能最先执行线程1


private Lock lock = new ReentrantLock(); // 实现锁的接口
/**
* 定义3个Condition
*/
private Condition condition_1 = lock.newCondition();
private Condition condition_2 = lock.newCondition();
private Condition condition_3 = lock.newCondition();

public void hah()throws InterruptedException {
lock.lock();
try {
if (flag == 1 ) {//线程1因为后边2个线程的短路判断，所以最先执行。

condition_1.await();//线程1等待
}

System.out.println("线程1:" + x++);
System.out.println("线程1:" + x++);
System.out.println("线程1:" + x++);
System.out.println();

flag = 1;//执行完以后把标记置为1
condition_2.signal();//唤醒线程2
}finally{
lock.unlock();
}
}

public void haha() throws InterruptedException{
lock.lock();
try {
if (flag == 2 || flag == 3) {//因为flag初始值为3，所以即使线程抢到资源也不会执行，这样保证了线程按照顺序执行
condition_2.await();
}
System.out.println("线程2:" + x++);
System.out.println("线程2:" + x++);
System.out.println("线程2:" + x++);
System.out.println();
flag = 2;//置为2
condition_3.signal();//唤醒线程3
} finally {
lock.unlock();
}
}

public void ha() throws InterruptedException {
lock.lock();
try {
if (flag == 3 || flag == 1) {{//因为flag初始值为3，最先执行的1线程将标记改为2  所以即使线程抢到资源也不会执行，保证线程2优先线程3执行
condition_3.await();

}

System.out.println("线程3:" + x++);
System.out.println("线程3:" + x++);
System.out.println("线程3:" + x++);
System.out.println();

flag = 3;
condition_1.signal();//唤醒线程1
}finally{
lock.unlock();
}
}