為什么 Spring 引導調度程序中的 @Async 任務不是每 1 秒運行一次

Question

我無法理解使用@Async注釋定義的方法的行為。 據我了解，該方法應每 1 秒執行一次。 但我認為並非如此。

@EnableAsync
@Component
public class AsyncSchedulingDemo {

    private static final SimpleDateFormat dateFormat = new SimpleDateFormat("MM/dd/yyyy HH:mm:ss");

    //every 1 second, INSTANT start of job but waits for the first job to finish hence takes 10 seconds
    //here the next execution will start after 10 seconds because the job takes 10 seconds to finish
    @Scheduled(fixedRate = 1000)
    public void performFixedRateTask_W_LongRunningJob() throws InterruptedException {
        System.out.println("Task performed every 1 second but waits for the first one to finish before the next execution starts " + dateFormat.format(new Date()));
        Thread.sleep(10000);
    }

    //should be executed every 1 second because of @Async
    //here the next execution should start IMMEDIATELY and does NOT wait for the first one to finish
    @Async
    @Scheduled(fixedRate = 1000)
    public void performFixedRateTask_With_Async() throws InterruptedException {
        System.out.println("Async Task performed every 1 second as it does NOT wait for the first one to finish " + dateFormat.format(new Date()));
        Thread.sleep(10000);
    }

}

控制台日志：

Task performed every 1 second but waits for the first one to finish before the next execution starts 05/13/2020 15:54:51
Async Task performed every 1 second as it does NOT wait for the first one to finish 05/13/2020 15:54:51

Task performed every 1 second but waits for the first one to finish before the next execution starts 05/13/2020 15:55:01
Async Task performed every 1 second as it does NOT wait for the first one to finish 05/13/2020 15:55:01

Task performed every 1 second but waits for the first one to finish before the next execution starts 05/13/2020 15:55:11
Async Task performed every 1 second as it does NOT wait for the first one to finish 05/13/2020 15:55:11

===更新===

如果我完全注釋掉第一個方法並再次執行應用程序，我會看到第二個方法每秒執行一次。 為什么？？ 第一種方法如何防止執行第二種方法？

控制台日志：

Async Task performed every 1 second as it does NOT wait for the first one to finish 05/13/2020 16:45:48
Async Task performed every 1 second as it does NOT wait for the first one to finish 05/13/2020 16:45:49
Async Task performed every 1 second as it does NOT wait for the first one to finish 05/13/2020 16:45:50
Async Task performed every 1 second as it does NOT wait for the first one to finish 05/13/2020 16:45:51

Answer 1

我認為，這是因為根據spring 文檔，用於執行@Scheduled注釋方法的線程的默認池大小為 1：“如果您不提供 'pool-size' 屬性，則默認線程池將只有一個線。”

由於第一種方法不是@Async ，它阻塞了唯一的線程。