java - 不明白ExecutorService#shutdown

Question

以下是ExecutorService#shutdown的javadoc

/**
 * Initiates an orderly shutdown in which previously submitted
 * tasks are executed, but no new tasks will be accepted.
 * Invocation has no additional effect if already shut down.
 *
 * <p>This method does not wait for previously submitted tasks to
 * complete execution.  Use {@link #awaitTermination awaitTermination}
 * to do that.
 *
 * @throws SecurityException if a security manager exists and
 *         shutting down this ExecutorService may manipulate
 *         threads that the caller is not permitted to modify
 *         because it does not hold {@link
 *         java.lang.RuntimePermission}{@code ("modifyThread")},
 *         or the security manager's {@code checkAccess} method
 *         denies access.
 */
void shutdown();

上面写着

1. 不会接受新任务
2. 威尔 NOT等待提交的任务完成

我对第一点没有疑问，但我认为执行器会等待提交的任务完成，如下面的代码:

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

public class Main {
    public static void main(String[] args) throws InterruptedException {
        ExecutorService es = Executors.newFixedThreadPool(1);
        es.submit(new Runnable() {
            @Override
            public void run() {
                System.out.println("starts to run 1");
                try {
                    Thread.sleep(10 * 1000);
                    System.out.println("end to run 1");
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        });

        es.submit(new Runnable() {
            @Override
            public void run() {
                System.out.println("starts to run 2");
                try {
                    Thread.sleep(10 * 1000);
                    System.out.println("end to run 2");
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        });
        Thread.sleep(1 * 1000);
        es.shutdown();

        System.out.println("Job is done");


    }


}

两个任务都提交了，由于池中只有一个线程，所以有一个任务正在运行，另一个在队列中等待调度。

但是，这两个任务最终都会运行。

所以，我想问javadoc This method does not wait for previously submitted tasks to complete execution 是什么意思？

Answer 1

这意味着shutdown方法立即返回。在返回调用者之前，它不会等待计划的和已运行的任务完成。这意味着 ExecutorService 仍然需要一些时间来清理并终止自身(在所有正在运行的任务完成后，它最终会这样做)。