线程的join方法和countdownlatch类
线程之间的状态有5种初始、就绪、运行、阻塞、死亡，大家应该都知道，线程在由运行态到阻塞态时有一种方法join。Join的功能和CountDownLatch类似，可以让所有子线程跑完再执行主线程。下面举例子说明两个的用法
1.线程的join方法，控制执行情况，实现主线程等待子线程。
我们可以拿Dota游戏来举例，在我们玩的时候可以进行单挑（Solo），玩过的应该不陌生，游戏我们认定为主线程，自己和对方定义为子线程，自己和对方的准备也就是加入A和B队伍中，加入队伍我们认定是子线程的任务。只有当己方和对方都准备好（进入各自队伍），游戏就会自动开始（对战平台自己触发的）
publicclass ThreadJoinShow {
privateclass ASubThread implements Runnable{
private String name;
public ASubThread(String name) {
this.name = name;
}
@Override
publicvoid run() {
System.out.println(name+"======正在加入游戏===");
try {
Thread.sleep(3000);
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println(name+"======准备好了===");
}
}
privateclass BSubThread implements Runnable{
private String name;
public BSubThread(String name) {
this.name = name;
}
@Override
publicvoid run() {
System.out.println(name+"======正在加入游戏===");
try {
Thread.sleep(3000);
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println(name+"======准备好了===");
}
}
@Test
publicvoid testNoJoin() throws InterruptedException {
System.out.println("魔兽初始界面加载请选择阵营====start");
ASubThread asub = new ASubThread("天灾方选手A");
BSubThread bsub = new BSubThread("近卫方选手B");
Thread at = new Thread(asub);
Thread bt = new Thread(bsub);
at.start();
bt.start();
System.out.println("魔兽争霸之Dota====进度条走完===进入游戏===end");
Thread.sleep(10000);//主线程暂停10s是为了防止主线程结束子线程也会跟着结束
}
@Test
publicvoid testJoin() throws InterruptedException {
System.out.println("Join版魔兽初始界面加载请选择阵营====start");
ASubThread asub = new ASubThread("Join版===天灾方选手A");
BSubThread bsub = new BSubThread("Join版===近卫方选手B");
Thread at = new Thread(asub);
Thread bt = new Thread(bsub);
at.start();
bt.start();
try {
at.join();
bt.join();
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println("Join版魔兽争霸之Dota====进度条走完===进入游戏===end");
Thread.sleep(10000);//主线程暂停10s是为了防止主线程结束子线程也会跟着结束
}
}
执行测试方法console控台打印日志分别如下：
魔兽初始界面加载请选择阵营====start
魔兽争霸之Dota====进度条走完===进入游戏===end
天灾方选手A======正在加入游戏===
近卫方选手B======正在加入游戏===
天灾方选手A======准备好了===
近卫方选手B======准备好了===
Join版魔兽初始界面加载请选择阵营====start
Join版===天灾方选手A======正在加入游戏===
Join版===近卫方选手B======正在加入游戏===
Join版===天灾方选手A======准备好了===
Join版===近卫方选手B======准备好了===
Join版魔兽争霸之Dota====进度条走完===进入游戏===end
由日志可以发现，用了join方法后，主线程会等待子线程执行完，所以正常的游戏流程应该用join版，只有大家都准备好了，才能进入游戏。
2.CountDownLatch类也可以实现上述的功能，就是等所有子任务都跑完了，主线程再往下执行。
CountDownLatch有两个方法是我们常用的：await();和countDown();await()函数用于阻塞当前线程直到CountDownLatch的计数值变为0；countDown()方法用于将当前CountDownLatch的计数值减1。举个例子，假设有个女子组合TF girls要参加中戏的艺考，三个人有表演唱歌有表演朗诵有表演舞蹈，只有都通过了，才能拿到中戏的录取通知书，代码如下： public class ThreadCountDownLatchShow {
class SingSongTask implements Runnable{
private CountDownLatch countDownLatch;
public SingSongTask(CountDownLatch countDownLatch) {
this.countDownLatch = countDownLatch;
}
@Override
publicvoid run() {
try {
System.out.println("===A表演唱歌的===start");
Thread.sleep(3000);
System.out.println("===A表演唱歌的==表演结束==end");
countDownLatch.countDown();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}
class ReadPoetryTask implements Runnable{
private CountDownLatch countDownLatch;
public ReadPoetryTask(CountDownLatch countDownLatch) {
this.countDownLatch = countDownLatch;
}
@Override
publicvoid run() {
try {
System.out.println("===B表演朗读的===start");
Thread.sleep(6000);
System.out.println("===B表演朗读的==表演结束==end");
countDownLatch.countDown();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}
class DanceTask implements Runnable{
private CountDownLatch countDownLatch;
public DanceTask(CountDownLatch countDownLatch) {
this.countDownLatch = countDownLatch;
}
@Override
publicvoid run() {
try {
System.out.println("===C表演跳舞的===start");
Thread.sleep(5000);
System.out.println("===C表演跳舞的==表演结束==end");
countDownLatch.countDown();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}
@Test
publicvoid testGetZhongxiNotice() throws InterruptedException {
System.out.println("===TF girls参加中戏考试===");
CountDownLatch countDownLatch = new CountDownLatch(3);
ExecutorService proctorExec = Executors.newFixedThreadPool(3);
proctorExec.execute(new SingSongTask(countDownLatch));
proctorExec.execute(new ReadPoetryTask(countDownLatch));
proctorExec.execute(new DanceTask(countDownLatch));
countDownLatch.await();
proctorExec.shutdown();
System.out.println("===TF girls参加中戏考试===考试结束===通过===发录取通知书==");
}
}
执行测试方法console控台打印日志分别如下：
===TF girls参加中戏考试===
===A表演唱歌的===start
===B表演朗读的===start
===C表演跳舞的===start
===A表演唱歌的==表演结束==end
===C表演跳舞的==表演结束==end
===B表演朗读的==表演结束==end
===TF girls参加中戏考试===考试结束===通过===发录取通知书==