c# - 迁移到 ASP CORE 3 : how to migrate backround services?(通过 AddHostedService 添加的服务卡住 Web 应用程序启动)

Question

迁移到 ASP Core3 后，此行卡住了 Web 应用程序启动过程(使用 VS 调试:浏览器已弹出但页面加载从未结束)

serviceCollection.AddHostedService<BackgroundService>();

它适用于 Core 2。

我在 ASP Core3 文档中看不到与 AddHostedService 相关的任何重大更改:

https://learn.microsoft.com/en-us/aspnet/core/migration/22-to-30?view=aspnetcore-3.0&tabs=visual-studio

似乎阻止后台服务器 StartAsync 阻止了 Web 应用程序启动。可能应该在 WebHost 中配置一些东西以使 StartAsync 再次异步？

后台服务代码如下:

public class MyBackgroundService : IHostedService
{
    private readonly BackgroundServiceHandle backgroundServiceHandle;
    private CancellationTokenSource tokenSource;

    public MyBackgroundService (BackgroundServiceHandle backgroundServiceHandle) => 
        this.backgroundServiceHandle = backgroundServiceHandle;


    public async Task StartAsync(CancellationToken cancellationToken)
    {
        tokenSource = CancellationTokenSource.CreateLinkedTokenSource(cancellationToken);
        while (cancellationToken.IsCancellationRequested == false)
        {
            try
            {
                await Task.Delay(TimeSpan.FromSeconds(3), cancellationToken).ConfigureAwait(false);

               // IMPORTANT: it seems that next line blocks the web app startup, but why this works in CORE 2? 
                var taskSettings = backgroundServiceHandle.Dequeue(tokenSource.Token); 

                // the work
            }
            catch (OperationCanceledException)
            {
                // execution cancelled
            }
        }
    }

    public Task StopAsync(CancellationToken cancellationToken)
    {
        tokenSource.Cancel();
        return Task.CompletedTask;
    }
}

public sealed class BackgroundServiceHandle : IDisposable
{
    private readonly BlockingCollection<TaskSettings> blockingCollection;

    public BackgroundServiceHandle() => blockingCollection = new BlockingCollection<TaskSettings>();

    public void Enqueue(TaskSettings settings) => blockingCollection.Add(settings);

    public TaskSettings Dequeue(CancellationToken token) => blockingCollection.Take(token);

    public void Dispose()
    {
        blockingCollection.Dispose();
    }
}

Answer 1

将基类从 IHostedService 移动到 BackgroundService并将 StartAsync 移动到protected override async Task ExecuteAsync(CancellationToken cancellationToken) 解决问题