新建了一个线程池，但是只能跑核心数量的线程，设置的最大线程数不起作用，是为什么？

@RestController
@RequestMapping("/test")
public class TestController {

   private ExecutorService executor = new ThreadPoolExecutor(3, 10, 20, TimeUnit.SECONDS,
           new ArrayBlockingQueue<Runnable>(20),
           new ThreadPoolExecutor.CallerRunsPolicy());

   @GetMapping("/thread")
   public String testThreadPool() {
       executor.execute(new MyTask("一號"));
       executor.execute(new MyTask("二號"));
       executor.execute(new MyTask("三號"));
       executor.execute(new MyTask("四號"));
       executor.execute(new MyTask("五號"));

       return "success";
   }
}
public class MyTask implements Runnable {

   private String name;

   public MyTask(String name) {
       this.name = name;
   }

   @Override
   public void run() {
       while (true) {
           System.out.println("------ 我是任务：" + name);

           try {
               Thread.sleep(1000L);
           } catch (InterruptedException e) {
               e.printStackTrace();
           }
       }
   }
}