【Java并发】10个线程处理完任务后，再合并处理，CountDownLatch的用法

代码

线程一起执行：

import java.util.*;
import java.util.concurrent.*;public class Main {public static List<String> getExecutorService() throws InterruptedException{System.out.println("开始执行多线程...");long startTime = System.currentTimeMillis();List<String> list = new ArrayList<>(); //存放返回结果CountDownLatch countDownLatch = new CountDownLatch(10);ExecutorService executorService = new ThreadPoolExecutor(10, 10, 0L,TimeUnit.MILLISECONDS, new LinkedBlockingQueue<Runnable>());for (int i = 0; i < 10; i++) {System.out.println("线程准备中...");Runnable runnable = new Runnable(){@Overridepublic void run() {try {Thread.sleep(3000);list.add(UUID.randomUUID().toString());System.out.println("当前线程name : " + Thread.currentThread().getName());} catch (InterruptedException e) {e.printStackTrace();} finally {countDownLatch.countDown();}}};executorService.execute(runnable);}System.out.println("countDownLatch.getCount(): " + countDownLatch.getCount());countDownLatch.await();  // 主线程阻塞，等计数器==0，唤醒主线程往下执行。System.out.println("countDownLatch.getCount(): " + countDownLatch.getCount());System.out.println("submit总共cost 时间：" + (System.currentTimeMillis() - startTime)/1000 + "秒");executorService.shutdown();  // 等内部线程执行完，停止线程return list;}public static void main(String[] args) {List<String> res = new ArrayList<>();try {res = getExecutorService();} catch (InterruptedException e) {e.printStackTrace();}System.out.println(res);}
}

一个一个线程执行

import java.util.*;
import java.util.concurrent.*;public class Main {public static List<String> getExecutorService() throws InterruptedException{System.out.println("开始执行多线程...");long startTime = System.currentTimeMillis();List<String> list = new ArrayList<>();  // 存放返回结果CountDownLatch countDownLatch = new CountDownLatch(10);ExecutorService executorService = new ThreadPoolExecutor(10, 10, 0L,TimeUnit.MILLISECONDS, new LinkedBlockingQueue<Runnable>());for (int i = 0; i < 10; i++) {System.out.println("线程准备中...");Runnable runnable = new Runnable(){@Overridepublic void run() {list.add(UUID.randomUUID().toString());System.out.println("当前线程name : " + Thread.currentThread().getName());countDownLatch.countDown();}};executorService.execute(runnable);try {Thread.sleep(1500);} catch (InterruptedException e) {e.printStackTrace();}}System.out.println("countDownLatch.getCount(): " + countDownLatch.getCount());countDownLatch.await();  // 主线程阻塞，等计数器==0，唤醒主线程往下执行。System.out.println("countDownLatch.getCount(): " + countDownLatch.getCount());System.out.println("submit总共cost 时间：" + (System.currentTimeMillis()-startTime)/1000 + "秒");executorService.shutdown();  // 等内部线程执行完，停止线程return list;}public static void main(String[] args) {List<String> res = new ArrayList<>();try {res = getExecutorService();} catch (InterruptedException e) {e.printStackTrace();}System.out.println(res);}
}

结果

线程一起执行：

Connected to the target VM, address: '127.0.0.1:65178', transport: 'socket'
开始执行多线程...
线程准备中...
线程准备中...
线程准备中...
线程准备中...
线程准备中...
线程准备中...
线程准备中...
线程准备中...
线程准备中...
线程准备中...
countDownLatch.getCount(): 10
当前线程name : pool-1-thread-6
当前线程name : pool-1-thread-10
当前线程name : pool-1-thread-3
当前线程name : pool-1-thread-9
当前线程name : pool-1-thread-8
当前线程name : pool-1-thread-5
当前线程name : pool-1-thread-2
当前线程name : pool-1-thread-4
当前线程name : pool-1-thread-1
当前线程name : pool-1-thread-7
countDownLatch.getCount(): 0
submit总共cost 时间：3秒
[9f8d1b1d-21a3-4ba3-8a2c-9701126e900f, d37227bd-bf9b-4c18-a7ab-e8f2a621f8c6, 71c8b258-b973-46e5-b4dc-5aba9c3f4fb5, ad1d8d4a-bdb8-4a14-8d36-3b4c62a06f2f, 50be045c-0cec-4d52-bb23-1476d7e40bf9, e87f4359-4382-4b2f-b520-ae598a0ce53e, 7e854a60-2566-4797-a2f8-1217b0c19214, efb2ab95-d632-4dd8-bade-57635c65e3ea, a1a88c3a-7563-4110-bc97-9b7eb257994b, 27d7eb60-c83b-4a21-8f46-1b5170aa49c3]

线程一个一个执行：

开始执行多线程...
线程准备中...
当前线程name : pool-1-thread-1
线程准备中...
当前线程name : pool-1-thread-2
线程准备中...
当前线程name : pool-1-thread-3
线程准备中...
当前线程name : pool-1-thread-4
线程准备中...
当前线程name : pool-1-thread-5
线程准备中...
当前线程name : pool-1-thread-6
线程准备中...
当前线程name : pool-1-thread-7
线程准备中...
当前线程name : pool-1-thread-8
线程准备中...
当前线程name : pool-1-thread-9
线程准备中...
当前线程name : pool-1-thread-10
countDownLatch.getCount(): 0
countDownLatch.getCount(): 0
submit总共cost 时间：15秒
[2176b202-744d-4e8b-9ce7-dab3e02738ef, 40f1cd8b-22c8-4260-8d71-6e1c9c9f15db, 5dce872b-4aef-4ef8-8558-b5d5935e95b3, 2fd450ac-8db6-4f6b-8caf-62c6fa667253, 0846b4d2-5a42-4cbc-bdde-32ad5cbc03ec, 2451fade-1af0-4c0e-adf2-84469f599d64, 5285a9a3-3075-4f8a-99a5-5adee23662be, 4f867908-6e1b-4840-a050-945c59481f1c, 70ecacd3-fc5b-4896-8b5d-cb2ec7e434d8, d5b2a439-0a86-4a5f-94f5-07bf53b674f9]