README.md

Ambient Context

Ambient operation logging and cancellation

GitHub and NuGet, NuGet.

How many times you have been writing something like this passing those tedious logger/token parameters?

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

Enough is enough.

Ambient Cancellation

What we about to do is to use a special Cancellation helper class like this:

        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");
            }
        }

Ambient Logging

Op class helps tracing execution in a logical order instead of chronological as everybody else :)

For example, the following code:

        static async Task MainAsync()
        {
            Op.Log.Subscribe(WriteLine);
            using (new Op())
                await Task.WhenAll(
                    from i in Range(0, 4)
                    select AlphaAsync());
        }

        private static async Task AlphaAsync()
        {
            using (new Op("Alpha function"))
                await BetaAsync();
        }

        private static async Task BetaAsync()
        {
            using (new Op())
            {
                Op.Trace("Waiting...");
                await Task.Delay(100);
                Op.Trace("Continue");
            }
        }

Will generate:

    MainAsync took 116 ms
      Alpha function took 109 ms
        BetaAsync took 108 ms
          Waiting... after 0 ms
          Continue after 108 ms
      Alpha function took 109 ms
        BetaAsync took 109 ms
          Waiting... after 0 ms
          Continue after 109 ms
      Alpha function took 109 ms
        BetaAsync took 109 ms
          Waiting... after 0 ms
          Continue after 109 ms
      Alpha function took 111 ms
        BetaAsync took 111 ms
          Waiting... after 0 ms
          Continue after 111 ms

Which is a way more readable…

ASP.NET Core support

Use AmbientContextAttribute on controller class or controller action method to support execution tracing and cancellation.

Your controller might look like this:

    [Route("/"), AmbientContext]    
    public class GreeterController
    {
        public GreeterController(Greeter greeter) => Greeter = greeter;
        Greeter Greeter { get; }

        [HttpGet]
        public async Task<string> Get() => await Greeter.GreetAsync();
    }

Where:

   public class Greeter
   {
       public async Task<string> GreetAsync()
       {
           using (new Op())
           {
               Op.Trace("Started waiting");
               await Task.Delay(100, Cancellation.Token);
               Op.Trace("Ready");

               return "Hello World";
           }
       }
   }

The expected output would be:

Hosting environment: Production
Content root path: C:\Proj\ambientcontext\Demo\bin\Debug\netcoreapp2.1\
Now listening on: http://localhost:5000
Now listening on: https://localhost:5001
Application started. Press Ctrl+C to shut down.
http://localhost:5000/ took 123 ms
  GreetAsync took 109 ms
    Started waiting after 0 ms
    Ready after 109 ms
http://localhost:5000/ took 100 ms
  GreetAsync took 100 ms
    Started waiting after 0 ms
    Ready after 100 ms

Please see the Demo project for more details.