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深入理解JUC:第四章:CountDownLatch倒计时器

南陵王梁枫 2022-05-16 阅读 43


理论:

深入理解JUC:第四章:CountDownLatch倒计时器_i++

CountDownLatch是一个非常实用的多线程控制工具类。常用的就下面几个方法:

CountDownLatch(int count) //实例化一个倒计数器,count指定计数个数
countDown() // 计数减一
await() //等待,当计数减到0时,所有线程并行执行

未使用CountDownLatch的代码:

public class Demo {

public static void main(String[] args) {
for (int i = 0; i < 5; i++) {
new Thread(()->{
System.out.println(Thread.currentThread().getName()+"\t 工作任务完成,离开公司");
},String.valueOf(i)).start();
}
System.out.println(Thread.currentThread().getName()+"\t 最后将公司门锁死,离开公司");
}
}

控制台:

深入理解JUC:第四章:CountDownLatch倒计时器_i++_02

使用CountDownLatch的代码:

public class Demo {

public static void main(String[] args) throws Exception{
CountDownLatch countDownLatch = new CountDownLatch(5);
for (int i = 0; i < 5; i++) {
new Thread(()->{
System.out.println(Thread.currentThread().getName()+"\t 工作任务完成,离开公司");
countDownLatch.countDown();
},String.valueOf(i)).start();
}
countDownLatch.await();
System.out.println(Thread.currentThread().getName()+"\t 最后将公司门锁死,离开公司");
}
}

控制台:

深入理解JUC:第四章:CountDownLatch倒计时器_ide_03

案例二:

package tst.project;

import java.util.concurrent.CountDownLatch;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

public class Test {

public static void main(String[] args) {
int tasks = 3;
final CountDownLatch latch = new CountDownLatch(tasks);
ExecutorService executorService = Executors.newFixedThreadPool(tasks);
executorService.submit(new Runnable() {
@Override
public void run() {
try {
Thread.sleep(5000);
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println("5秒完成:"+latch);
latch.countDown();
}
});
executorService.submit(new Runnable() {
@Override
public void run() {
try {
Thread.sleep(3000);
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println("3秒完成:"+latch);
latch.countDown();
}
});
executorService.submit(new Runnable() {
@Override
public void run() {
try {
Thread.sleep(1000);
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println("1秒完成:"+latch);
latch.countDown();
}
});
executorService.shutdown();
try {
latch.await();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}

控制台:

深入理解JUC:第四章:CountDownLatch倒计时器_ide_04 




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