Calling method with @Async annotation called after to much time in spring boot

I am using java-11 and spring boot 2.3.8.RELEASE in my project.

In my project, I got the issue in calling @async method.

when i call @async method sometimes it called after to many hours. in most of the cases it executes at the time but sometime it takes to many hours to call the method.

below is my code

public void methodA(){
     logger.info("going to call async method");
     this.methodB();
     logger.info("async method execution completed");
}

@Async
public void methodB(){
      logger.info("inside async method");
}

when i checked logs for above then it i got o/p as below

2023-05-29 03:36:36.893  INFO 3382750 --- [http-nio-auto-1-exec-236] com.demo.web.service      : going to call async method

2023-05-29 04:53:08.893  INFO 3382750 --- [http-nio-auto-1-exec-236] com.demo.web.service      : inside async method

2023-05-29 04:53:08.893  INFO 3382750 --- [http-nio-auto-1-exec-236] com.demo.web.service      : async method execution completed

I don't understand why this is happening.
Sometime it works well as expected and sometime it's working like this

Any help is appreciated

Please guide. Thanks

> . in most of the cases it executes at the time but sometime it takes to many hours to call the method.
> Blockquote

thread issue. If the available thread is busy for other task, you must wait maybe many hours.

1. calling the async method from within the same class — won't work. you may see the detail https://www.baeldung.com/spring-async

2. you should create a ThreadPool and its size should bigger than 1, you may see the detail https://spring.io/guides/gs/async-method/