这篇文章非原创,来自两位大神的代码:
常用的两种方式:
ExecutorService taskExecutor = Executors.newFixedThreadPool(4);
while(...) {
taskExecutor.execute(new MyTask());
}
taskExecutor.shutdown();
try {
taskExecutor.awaitTermination(Long.MAX_VALUE, TimeUnit.NANOSECONDS);
} catch (InterruptedException e) {
...
}
CountDownLatch latch = new CountDownLatch(totalNumberOfTasks);
ExecutorService taskExecutor = Executors.newFixedThreadPool(4);
while(...) {
taskExecutor.execute(new MyTask());
}
try {
latch.await();
} catch (InterruptedException E) {
// handle
}
然后在线程方法中加入:
try {
...
} catch (Exception e) {
e.printStackTrace();
}finally {
countDownLatch.countDown();
}
作者建议用第二种方式,即用 CountDownLatch 来实现。
完整实例如下:
我们先定义一个 Runnable 类:CountDownLatchRunnable
关键点1:我们要通过 CountDownLatch 来计数,因此我需要把 CountDownLatch 对象传到这个 Runnable 类中。
关键点2:每次执行完后,一定要 countDownLatch.countDown()
@Slf4j
public class CountDownLatchRunnable implements Runnable {
private final String command;
private final CountDownLatch countDownLatch;
public CountDownLatchRunnable(String command, CountDownLatch countDownLatch) {
this.command = command;
this.countDownLatch = countDownLatch;
}
@Override
public void run() {
log.info(Thread.currentThread().getName() + " start. Command = " + command);
processCommand(command);
log.info(Thread.currentThread().getName() + " finish.");
}
private void processCommand(String command) {
log.info(Thread.currentThread().getName() + ":, doing work:" + command);
try {
Thread.sleep(1000);
} catch (Exception e) {
e.printStackTrace();
} finally {
countDownLatch.countDown();
}
}
}
然后实现运行:
@Slf4j
public class Run {
public static void main(String[] args) throws InterruptedException {
log.info("Main thread start.");
int theadNum = 3;
// CountDownLatch 需要将对象传入需要'等待完成'的线程对象中
CountDownLatch countDownLatch = new CountDownLatch(theadNum);
ExecutorService executorService = Executors.newFixedThreadPool(theadNum);
Runnable worker = new CountDownLatchRunnable("Task", countDownLatch);
// 创建5个线程, 提交到线程池
for (int i = 0; i < theadNum; i++) {
executorService.execute(worker); // 同一个实例对象
}
// 等待所有线程执行完成(线程阻塞)
countDownLatch.await();
log.info("Main thread finish.");
// 停止接受新任务,当已有任务将执行完,关闭线程池
executorService.shutdown();
// 等待线程池中所有的任务执行完成, 前提是执行了 shutdown
while (!executorService.isTerminated()) {
// 等待所有线程执行完成
}
log.info("exit");
}
}
运行结果如下:
Connected to the target VM, address: '127.0.0.1:32229', transport: 'socket'
[zhang-console] INFO 2023-11-18 03:07:48 j.b.j.t.t.t2_wait_countdownlatch.Run: Main thread start.
[zhang-console] INFO 2023-11-18 03:07:48 j.b.j.t.t.t.CountDownLatchRunnable: pool-1-thread-1 start. Command = Task
[zhang-console] INFO 2023-11-18 03:07:48 j.b.j.t.t.t.CountDownLatchRunnable: pool-1-thread-1:, doing work:Task
[zhang-console] INFO 2023-11-18 03:07:48 j.b.j.t.t.t.CountDownLatchRunnable: pool-1-thread-2 start. Command = Task
[zhang-console] INFO 2023-11-18 03:07:48 j.b.j.t.t.t.CountDownLatchRunnable: pool-1-thread-2:, doing work:Task
[zhang-console] INFO 2023-11-18 03:07:48 j.b.j.t.t.t.CountDownLatchRunnable: pool-1-thread-3 start. Command = Task
[zhang-console] INFO 2023-11-18 03:07:48 j.b.j.t.t.t.CountDownLatchRunnable: pool-1-thread-3:, doing work:Task
[zhang-console] INFO 2023-11-18 03:07:49 j.b.j.t.t.t.CountDownLatchRunnable: pool-1-thread-3 finish.
[zhang-console] INFO 2023-11-18 03:07:49 j.b.j.t.t.t2_wait_countdownlatch.Run: Main thread finish.
[zhang-console] INFO 2023-11-18 03:07:49 j.b.j.t.t.t.CountDownLatchRunnable: pool-1-thread-1 finish.
[zhang-console] INFO 2023-11-18 03:07:49 j.b.j.t.t.t.CountDownLatchRunnable: pool-1-thread-2 finish.
[zhang-console] INFO 2023-11-18 03:07:49 j.b.j.t.t.t2_wait_countdownlatch.Run: exit
Disconnected from the target VM, address: '127.0.0.1:32229', transport: 'socket'