IHostedService和Asp.net Core中计划任务的Task有什么区别? [英] What's the difference between IHostedService and Task for scheduled task in asp.net core?
问题描述
我想每5分钟将数据从内存数据库更新到关系数据库
I wanna update data from an in-memory database to a relational database every 5 minutes.
每个人都建议我使用源.net核心中的 IHostedService 或其他一些第三方程序包，例如 Hangfire .
Everyone suggests me to use the IHostedService from origin .net core or some other third-party package such as Hangfire.
鉴于此，我认为它太麻烦了，因为它必须编写很多代码.
Whereas, I think it is so troublesome for it must code much.
我有一个奇怪的想法，可以通过循环任务来实现它，例如:
I have a strange idea that achieves it by the looping task, for example:
using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading;
using System.Threading.Tasks;
using Microsoft.AspNetCore.Mvc;
namespace WebApplication3.Controllers
{
[Route("api/")]
public class TestController : Controller
{
public TestController()
{
Task.Run(() => {
while (true)
{
Console.WriteLine("123");//code something to transfer data to the database
Thread.Sleep(5000);
//Task.Delay(5000);
}
});
}
[Route("ABC")]
public void ABC()
{
}
}
}
此外，它是如此奇怪，以至于如果我使用 Task.Delay 都不会延迟任何延迟，而如果我使用 Thread.Sleep 则可以正常工作.
What's more, it is so strange that it won't delay any if I use the Task.Delay while it works well if I use the Thread.Sleep.
我想知道为什么没有人通过 System.Threading.Tasks 的 Task 实现它吗?
I wonder why no people achieve it by the Task of System.Threading.Tasks?
也许这是一个愚蠢的问题，但我想找到原因.谢谢.
Maybe it is a stupid question but I want to find the reason. Thank you.
推荐答案
通常是由于该过程的工作原理.我假设您没有将 Task.Run()放在控制器上，而是放在启动上.如果在控制器上使用它，它将仅在每个请求中启动一个新线程.
Generally is because of how the process works. I will assume that you don't place the Task.Run() on the controller but on the startup. If you use it on the controller it will simply start a new thread in each and every request.
ASP.NET Core的工作方式是启动一个进程，侦听传入的请求，并为每个请求创建一个新线程.请记住，使用任务运行创建新线程与在后台运行的线程不同.为了使其在后台运行，您需要一个新进程，而不是线程池中的线程.通常，这将是一个始终运行且永远不会释放给服务器其他请求的线程.
The way ASP.NET Core works is that it starts a process that listens for incoming request and for each request it creates a new thread for it. Remember that creating a new thread with task run is not the same as something running in the background. In order for it to run on the background you would require a new process not a thread from the thread pool. Generally this will be a thread that will always run and never be freed to server other requests.
此外，它是如此奇怪，以至于如果我使用Task.Delay都不会延迟任何延迟，而如果我使用Thread.Sleep则可以正常工作.
What's more, it is so strange that it won't delay any if I use the Task.Delay while it works well if I use the Thread.Sleep.
使用Task.Delay.它需要async关键字，并且不会阻塞线程.您可能没有使用 await 关键字.
Use Task.Delay. It requires the async keyword and it doesnt block the thread. You were probably not using the await keyword.
我想知道为什么没有人通过System.Threading.Tasks的任务实现它吗?
I wonder why no people achieve it by the Task of System.Threading.Tasks?
通常，您可以防御性地实现它，但重要的是对它的控制.每5分钟，您的cpu和io使用量就会猛增一次.但是，如果将应用程序拆分到同一主机的2个容器中，则可以控制每个容器具有多少CPU分配，从而使API的性能不会出现峰值.
Generally you could defently implement it but the important thing is the control you have over it. Every 5 minutes your cpu and io usage will spike. But if you split the application in 2 containers in the same host, you can control how much CPU allocation each container will have thus allowing you not to have spikes in performance for the API.
关于托管服务，从文档中可以看到ASP.NET Core启动Web服务器，然后在其他服务上启动IHostedService.这就是为什么它是首选.这是后台任务，而不是API线程池中的线程
About hosted service as you can see from the documentation ASP.NET Core starts a web server and then starts a IHostedService on a different service. Thats why it's preferred. It's a background task not a thread from the thread pool of your API
关于IHostedService，我错了，它不会启动新进程，但是您应该使用它只是因为它更易于管理，并且可以轻松交换新进程并以更加结构化的方式进行维护.
About the IHostedService I was wrong it doesn't start a new process but you should use it just because it's more manageable and it allows you swap a new process easily and maintain in a much more structured way.
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