操作取消

Question

简洁适用于国王，因为它需要上下文，而上下文则适用于国王。我。

GitHub和NuGet

您已经写了多少次这样的东西，传递那些乏味的记录器/令牌参数？

interface IMyService
{
    void Method1(…, ILogger logger, CancellationToken token);
    void Method2(…, ILogger logger, CancellationToken token);
    …
}

够了够了。有关环境日志记录，请参见这里。下面是关于环境取消。

我们将要做的是使用一个特殊的Cancellation助手类，如下所示：

    static void Main(string[] args)
    {
        using (new Cancellation())
        {
            Task.Run(PingAsync);
            ReadLine();
            Cancellation.Request();
            ReadLine();
        }
    }

    static async Task PingAsync()
    {
        try
        {
            while (!Cancellation.Requested)
            {
                await Task.Delay(100, Cancellation.Token);
                WriteLine("Ping");
            }

            Cancellation.ThrowIfRequested();
        }
        catch(OperationCanceledException)
        {
            WriteLine("Ping cancelled");
        }
    }

其中Cancellation被定义为：

public class Cancellation : IDisposable
{
    static AsyncLocal<CancellationTokenSource> Context { get; } = 
        new AsyncLocal<CancellationTokenSource>();

    public Cancellation()
        : this(CancellationToken.None)
    {
    }

    public Cancellation(CancellationToken cancellationToken)
        : this(cancellationToken, Timeout.InfiniteTimeSpan)
    {
    }

    public Cancellation(int timeout)
        : this(TimeSpan.FromMilliseconds(timeout))
    {
    }

    public Cancellation(TimeSpan timeout)
        : this(CancellationToken.None, timeout)
    {
    }

    public Cancellation(CancellationToken cancellationToken, int timeout)
        : this(cancellationToken, TimeSpan.FromMilliseconds(timeout))
    {
    }

    public Cancellation(CancellationToken cancellationToken, TimeSpan timeout)
    {
        Parent = Context.Value;
        Context.Value = CancellationTokenSource
            .CreateLinkedTokenSource(cancellationToken);

        Context.Value.CancelAfter(timeout);
    }

    public void Dispose()
    {
        var cts = Context.Value;
        Context.Value = Parent;
        cts.Dispose();
    }

    CancellationTokenSource Parent { get; }
    public static CancellationToken Token => 
         Context.Value?.Token ?? CancellationToken.None;

    public static void Request() => Context.Value?.Cancel();
    public static bool Requested => Token.IsCancellationRequested;
    public static void ThrowIfRequested() => Token.ThrowIfCancellationRequested();        
}

Answer 1

不确定它是否可以算作答案，但最重要的缺失部分是以下ASP.NET核心属性：

public class AmbientContextAttribute : Attribute, IAsyncActionFilter
{
    public async Task OnActionExecutionAsync(ActionExecutingContext context, ActionExecutionDelegate next)
    {
        using (new Op(context.HttpContext.Request.GetDisplayUrl()))
        using (new Cancellation(context.HttpContext.RequestAborted))
            await next();
    }
}