.net 核心`IHostedService` 是否应该启动一个新线程

Question

.net coreBackgroundService或IHostedService的 start 方法是异步的：

//IHostedService
Task StartAsync(CancellationToken cancellationToken);
//BackgroundService
Task ExecuteAsync(CancellationToken stoppingToken);

那么我应该在ExecuteAsync/StartAsync方法中编写所有逻辑，还是应该启动一个新线程并立即返回？

例如，以下哪两个是正确的实现？

1.

protected override async Task ExecuteAsync(CancellationToken stoppingToken)
{
    new Thread(async () => await DoWork(stoppingToken)).Start();

    await Task.CompletedTask;
}

private async Task DoWork(CancellationToken stoppingToken) 
{
    while (!stoppingToken.IsCancellationRequested)
        //actual works
}

2.

protected override async Task ExecuteAsync(CancellationToken stoppingToken)
{
    while (!stoppingToken.IsCancellationRequested)
    {
        //actual works
        await Task.Delay(1000);//e.g
    }
}

从语义上讲，我认为第二个似乎是正确的，但是如果有几个IHostedServices，它们可以与第二种形式并行运行吗？

编辑 1

我还编写了一个示例程序，说明托管服务本身不是作为单独的线程运行的。

在"Waiting for signal.."我键入 a 之前，不会将消息写入控制台q：

using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Hosting;
using System;
using System.Threading;
using System.Threading.Tasks;

namespace BackgroundTaskTest
{
    public class Program
    {
        public static async Task Main(string[] args)
        {
            var host = new HostBuilder()
                .ConfigureServices((hostContext, services) =>
                {
                    IConfiguration config = hostContext.Configuration;

                    //register tasks
                    services.AddHostedService<ReadService>();
                    services.AddHostedService<BlockService>();
                })
                .UseConsoleLifetime()
                .Build();

            await host.RunAsync();
        }
    }

    public static class WaitClass
    {
        public static AutoResetEvent Event = new AutoResetEvent(false);
    }

    public class ReadService : BackgroundService
    {
        protected override async Task ExecuteAsync(CancellationToken stoppingToken)
        {
            while (!stoppingToken.IsCancellationRequested)
            {
                var c = Console.ReadKey();
                if (c.KeyChar == 'q')
                {
                    Console.WriteLine("\nTrigger event");
                    WaitClass.Event.Set();
                }
                await Task.Delay(1);
            }
        }
    }

    public class BlockService : BackgroundService
    {
        protected override Task ExecuteAsync(CancellationToken stoppingToken)
        {
            while (!stoppingToken.IsCancellationRequested)
            {
                Console.WriteLine("Waiting for signal..");
                WaitClass.Event.WaitOne();
                Console.WriteLine("Signal waited");
            }
            return Task.CompletedTask;
        }
    }
}

Answer 1

只需使用async/实现它await，如您的第二个示例所示。不需要额外的Thread.

旁注：Thread应该只用于 COM 互操作；如今，对于Thread. 只要您输入new Thread，您就已经拥有遗留代码。