.net core BackgroundService
orIHostedService
的启动方法是异步的:
//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
}
}
语义上我认为第二种似乎是对的,但是如果有几个IHostedService
s,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来说明托管服务本身并不是作为单独的线程运行的。
在我输入 a 之前,该消息"Waiting for signal.."
不会被写入控制台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;
}
}
}