如何在ASP.net核心中手动重新启动BackgroundService

Question

我创建BackgroundService:

public class CustomService : BackgroundService
{
protected override async Task ExecuteAsync(CancellationToken cancellationToken)
{
//...
}
}

我添加到项目中：

public class Startup
{
//...
public void ConfigureServices(IServiceCollection services)
{
services.AddHostedService<CustomService>();
//...
}
//...
}

如何从其他类中找到CustomService？
如何重新开始？

Answer 1

只为调用StartAsync:创建一个接口

public interface ICustomServiceStarter
{
Task StartAsync(CancellationToken token = default);
}
public class CustomService : BackgroundService, ICustomServiceStarter
{
//...
Task ICustomServiceStarter.StartAsync(CancellationToken token = default) => base.StartAsync(token);
//...
}

将接口注册为单例：

public class Startup
{
//...
public void ConfigureServices(IServiceCollection services)
{
//...
services.AddSingleton<ICustomServiceStarter, CustomService>();
}
//...
}

并在需要时注入ICustomServiceStarter：

public class MyServiceControllerr : Controller
{
ICustomServiceStarter _starter;
public MyServiceController(ICustomServiceStarter starter)
{
_starter = starter;
}
[HttpPost]
public async Task<IActionResult> Start()
{
await _starter.StartAsync();
return Ok();
}
}

Answer 2

当涉及到控制器的操作时，使用"等待BackgroundService.StartAsync"；是长时间运行任务的错误方式。

例如，主ussue可能是请求的超时取决于代理设置。

下面是一个如何使BackgroundService可重新启动的示例。

后台服务实现：

public class MyBackgroundService: BackgroundService
{
private volatile bool _isFinished = false;
private SemaphoreSlim _semaphore = new SemaphoreSlim(0,1);
protected override async Task ExecuteAsync(CancellationToken stoppingToken)
{
_isFinished = false;
// DoSomeWork
_isFinished = true;
await WaitToRestartTask(stoppingToken);
}
private async Task WaitToRestartTask(CancellationToken stoppingToken)
{
// wait until _semaphore.Release()
await _semaphore.WaitAsync(stoppingToken);
// run again
await base.StartAsync(stoppingToken);
}
public void RestartTask()
{
if (!_isFinished)
throw new InvalidOperationException("Background service is still working");
// enter from _semaphore.WaitAsync
_semaphore.Release();
}  
}

控制器的动作(例如(：

public async Task<IActionResult> Restart()
{
var myBackgroundService= _serviceProvider.GetServices<IHostedService>()
.OfType<MyBackgroundService>()
.First();
try
{
myBackgroundService.RestartTask();
return Ok($"MyBackgroundService was restarted");
}
catch (InvalidOperationException exception)
{
return BadRequest(exception.Message);
}
}