使用Thread的join方法
- package com.qcy.testThreadFinish;
- /**
- * @author qcy
- * @create 2020/09/09 17:05:23
- */
- public class Case1 {
- public static void main(String[] args) throws InterruptedException {
- Thread t1 = new Thread(() -> {
- try {
- Thread.sleep(3000);
- } catch (InterruptedException e) {
- e.printStackTrace();
- }
- });
- t1.start();
- Thread t2 = new Thread(() -> {
- try {
- Thread.sleep(3000);
- } catch (InterruptedException e) {
- e.printStackTrace();
- }
- });
- t2.start();
- t1.join();
- t2.join();
- System.out.println("主线程结束");
- }
- }
join()方法使得主线程等待子线程执行结束,阻塞的是主线程。其底层原理,可以参考我的这篇文章你真得懂Thread.join吗?
使用线程池的isTerminated方法
- package com.qcy.testThreadFinish;
- import java.util.concurrent.ExecutorService;
- import java.util.concurrent.Executors;
- /**
- * @author qcy
- * @create 2020/09/09 17:05:23
- */
- public class Case2 {
- public static void main(String[] args) {
- ExecutorService pool = Executors.newFixedThreadPool(3);
- pool.execute(() -> {
- try {
- Thread.sleep(2000);
- } catch (InterruptedException e) {
- e.printStackTrace();
- }
- });
- pool.execute(() -> {
- try {
- Thread.sleep(2000);
- } catch (InterruptedException e) {
- e.printStackTrace();
- }
- });
- //不再接受新的任务
- pool.shutdown();
- while (true) {
- //手动循环确实效率很低,不推荐
- if (pool.isTerminated()) {
- System.out.println("线程池中的任务执行结束");
- break;
- }
- }
- System.out.println("主线程结束");
- }
- }
isTerminated,当调用shutdown()方法后,并且所有提交的任务完成后才会返回为true
这里直接使用了固定大小的线程池,线程池的参数在面试中也经常被问到,对线程池不熟悉的同学,可以参考我的这篇文章说说线程池
使用Future机制
- package com.qcy.testThreadFinish;
- import java.util.concurrent.ExecutionException;
- import java.util.concurrent.ExecutorService;
- import java.util.concurrent.Executors;
- import java.util.concurrent.Future;
- /**
- * @author qcy
- * @create 2020/09/09 17:05:23
- */
- public class Case4 {
- public static void main(String[] args) throws ExecutionException, InterruptedException {
- ExecutorService pool = Executors.newFixedThreadPool(3);
- Future<Integer> task1 = pool.submit(() -> {
- try {
- Thread.sleep(2000);
- } catch (InterruptedException e) {
- e.printStackTrace();
- }
- return 2;
- });
- Future<Integer> task2 = pool.submit(() -> {
- try {
- Thread.sleep(2000);
- } catch (InterruptedException e) {
- e.printStackTrace();
- }
- return 3;
- });
- //不再接受新的任务
- pool.shutdown();
- //get方法为阻塞获取
- System.out.println("task1的运行结果:" + task1.get());
- System.out.println("task2的运行结果:" + task2.get());
- System.out.println("主线程结束");
- }
- }
Future机制,可以参考我的另外一篇博客谈谈Future、Callable、FutureTask关系
使用CountDownLatch
- package com.qcy.testThreadFinish;
- import java.util.concurrent.CountDownLatch;
- /**
- * @author qcy
- * @create 2020/09/09 17:05:23
- */
- public class Case5 {
- public static void main(String[] args) throws InterruptedException {
- CountDownLatch latch = new CountDownLatch(2);
- Thread t1 = new Thread(() -> {
- try {
- Thread.sleep(3000);
- } catch (InterruptedException e) {
- e.printStackTrace();
- } finally {
- latch.countDown();
- }
- });
- t1.start();
- Thread t2 = new Thread(() -> {
- try {
- Thread.sleep(3000);
- } catch (InterruptedException e) {
- e.printStackTrace();
- } finally {
- latch.countDown();
- }
- });
- t2.start();
- latch.await();
- System.out.println("主线程结束");
- }
- }
每调用一次countDown方法,计数器会减1,在计数器减为0之前,await方法将会阻塞主线程。有关CountDownLatch的底层原理,可以参考我的另外一篇博客CountDownLatch实现原理
使用CompletableFuture
- package com.qcy.testThreadFinish;
- import java.util.concurrent.CompletableFuture;
- import java.util.concurrent.ExecutionException;
- /**
- * @author qcy
- * @create 2020/09/09 17:05:23
- */
- public class Case6 {
- public static void main(String[] args) throws InterruptedException, ExecutionException {
- CompletableFuture<Integer> cf1 = CompletableFuture.supplyAsync(() -> {
- try {
- Thread.sleep(3000);
- } catch (InterruptedException e) {
- e.printStackTrace();
- }
- return 2;
- });
- CompletableFuture<Integer> cf = CompletableFuture.supplyAsync(() -> {
- try {
- Thread.sleep(3000);
- } catch (InterruptedException e) {
- e.printStackTrace();
- }
- return 3;
- }).thenCombine(cf1, (result1, result2) -> result1 * result2);
- //get方法为阻塞获取
- System.out.println("计算结果为" + cf.get());
- System.out.println("主线程结束");
- }
- }
等到两个子任务都完成后,输出两数之积,再执行主线程。对CompletableFuture不熟悉的同学,可以参考我的这一篇文章什么,你还不会用CompletableFuture?