今天在工作群里，领导发了一个代码片段的截图。并且要大家对这种代码进行排查。
这个代码逻辑很明显。通过线程池异步执行子任务，然后主线程阻塞。直到所有子任务执行完毕。
他采取的办法是，主线程在死循环对taskQueue进行isEmpty判断。如果有多个这种代码片段存在，这可能导致CPU飙升。而且子任务执行异常的话，有可能会导致下面的while死循环。
通过JUC实现线程同步
juc包下就有很这种场景的并发工具类。不要在自己写while(true)了。
- CountDownLatch
- CompletableFuture
2种方式的实现代码都很简单，这里不做过多说明了。
package io.springcloud.test;
import java.util.LinkedList;
import java.util.List;
import java.util.concurrent.CompletableFuture;
import java.util.concurrent.CountDownLatch;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.ThreadLocalRandom;
import lombok.extern.slf4j.Slf4j;
@Slf4j
public class MainTest {
public static void main(String[] args) throws Exception {
// CountDownLatch
test1();
// CompletableFuture
test2();
}
public static void test2() throws InterruptedException, ExecutionException {
ExecutorService executor = Executors.newFixedThreadPool(2); // 2个线程
LinkedList<String> queue = new LinkedList<String>(List.of("1", "2", "3", "4", "5"));
CompletableFuture<?>[] completableFutureArray = new CompletableFuture<?>[queue.size()];
for (int i = 0; i < queue.size(); i++) {
String val = queue.get(i);
// 使用线程池异步执行任务
CompletableFuture<Void> completableFuture = CompletableFuture.runAsync(() -> {
try {
Thread.sleep(ThreadLocalRandom.current().nextLong(1000, 2000));
} catch (InterruptedException e) {
e.printStackTrace();
}
log.info("val = {}", val);
}, executor);
completableFutureArray[i] = completableFuture;
}
CompletableFuture<Void> future = CompletableFuture.allOf(completableFutureArray);
// 阻塞，直到执行完毕
future.join();
log.info("执行完毕");
executor.shutdown();
}
public static void test1() throws InterruptedException {
LinkedList<String> queue = new LinkedList<String>(List.of("1", "2", "3", "4", "5"));
CountDownLatch countDownLatch = new CountDownLatch(queue.size());
for (String val : queue) {
new Thread(() -> {
try {
Thread.sleep(ThreadLocalRandom.current().nextLong(1000, 2000));
} catch (InterruptedException e) {
e.printStackTrace();
}
log.info("val = {}", val);
countDownLatch.countDown();
}).start();
}
countDownLatch.await();
log.info("执行完毕");
}
}
日志输出
17:25:39.367 [Thread-4] INFO io.springcloud.test.MainTest - val = 5
17:25:39.459 [Thread-3] INFO io.springcloud.test.MainTest - val = 4
17:25:39.757 [Thread-0] INFO io.springcloud.test.MainTest - val = 1
17:25:39.785 [Thread-1] INFO io.springcloud.test.MainTest - val = 2
17:25:40.131 [Thread-2] INFO io.springcloud.test.MainTest - val = 3
17:25:40.131 [main] INFO io.springcloud.test.MainTest - 执行完毕
17:25:41.369 [pool-1-thread-1] INFO io.springcloud.test.MainTest - val = 1
17:25:41.389 [pool-1-thread-2] INFO io.springcloud.test.MainTest - val = 2
17:25:42.694 [pool-1-thread-2] INFO io.springcloud.test.MainTest - val = 4
17:25:42.909 [pool-1-thread-1] INFO io.springcloud.test.MainTest - val = 3
17:25:43.781 [pool-1-thread-2] INFO io.springcloud.test.MainTest - val = 5
17:25:43.781 [main] INFO io.springcloud.test.MainTest - 执行完毕
