java并发初探CountDownLatch
CountDownLatch是同步工具类能够允许一个或者多个线程等待直到其他线程完成操作。
当前前程A调用CountDownLatch的await方法进入阻塞（LockSupportd的park方法），
其他线程调用CountDownLatch调用countDown()，CountDownLatch的内部变量
count为零时，线程A唤醒。
* A synchronization aid that allows one or more threads to wait until
* a set of operations being performed in other threads completes.
*
例子
package com.java.javabase.thread.base.concurrent.lock;
import lombok.extern.slf4j.Slf4j;
import java.util.concurrent.CountDownLatch;
/**
* @author
*/
@Slf4j
public class CountDownLatchTest {
private static CountDownLatch countDownLatch = new CountDownLatch(5);
public static void main(String[] args) {
new Thread() {
@Override
public void run() {
try {
log.info("thread {} call wait ",Thread.currentThread().getName());
sleep(1000);
countDownLatch.await();
log.info("thread {} end ",Thread.currentThread().getName());
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}.start();
for (int i = 0; i < 5; i++) {
new Thread() {
@Override
public void run() {
log.info("thread {} run ",Thread.currentThread().getName());
try {
sleep(1000);
} catch (InterruptedException e) {
e.printStackTrace();
}
countDownLatch.countDown();
}
}.start();
}
log.info("current thread is {}",Thread.currentThread().getName());
try {
countDownLatch.await();
log.info("thread is {} end",Thread.currentThread().getName());
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}
例子结果
2019-08-09 17:40:10,492 [Thread-1] INFO CountDownLatchTest - thread Thread-1 run
2019-08-09 17:40:10,492 [Thread-3] INFO CountDownLatchTest - thread Thread-3 run
2019-08-09 17:40:10,492 [Thread-2] INFO CountDownLatchTest - thread Thread-2 run
2019-08-09 17:40:10,492 [Thread-0] INFO CountDownLatchTest - thread Thread-0 call wait
2019-08-09 17:40:10,492 [main] INFO CountDownLatchTest - current thread is main
2019-08-09 17:40:10,492 [Thread-4] INFO CountDownLatchTest - thread Thread-4 run
2019-08-09 17:40:10,492 [Thread-5] INFO CountDownLatchTest - thread Thread-5 run
2019-08-09 17:40:11,491 [main] INFO CountDownLatchTest - thread is main end
2019-08-09 17:40:11,491 [Thread-0] INFO CountDownLatchTest - thread Thread-0 end