Category Archives: C#

C# – Consume non-async API’s as async

Posted on by
Reply

Now that we have the new nifty async support built into C# you might wonder how you can access your old API’s as if they were async.

Now before I show any code, I have to warn that the code posted here will only wrap your existing sync methods as a Task of T.
You will be able to consume them as if they were async, and in some cases this might be enough, and in other cases, such as IO scenarios, you really should rewrite the methods to use the proper async versions of the IO methods.

The wrapper code provided here may still be a decent start for you to do this, since you can start migrating code to use async calls, while you rewrite the methods that need rewriting later.


    class Program
    {
        static void Main(string[] args)
        {
            Consumer();
            Console.WriteLine("----");
            Console.ReadLine();
        }


        private async static void Consumer()
        {
            //consume the sync method as if it was async
            var b = await Wrap(() => NonAsyncMethod(1, ""));
            Console.WriteLine("got result back {0}",b);
        }

        //this might be one of your old or 3rd party methods
        private static int NonAsyncMethod(int a, string b)
        {
            System.Threading.Thread.Sleep(2000); //emulate some slow code
            return 5;
        }

        private static Task<T> Wrap<T>(Func<T> selector)
        {
            return Task.Factory.StartNew(selector);
        }
    }

Fake Fibers using Async CTP

Posted on by
2

This is another PoC, building recursive code with continuations using the Async CTP.

The code creates a fake fiber, which can be suspended and resumed, thus allowing us to “step” through its actions.
This technique could be useful when building an interpreting language where you might want to step through the expressions.

    using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Threading;
using System.Runtime.CompilerServices;


namespace ConsoleApplication7
{
    class Program
    {
        static void Main(string[] args)
        {
            FakeFiber f = new MyFiber();

            f.Run();
            while (true)
            {
                //tell fiber to continue
                f.Continue();
                Console.ReadLine();
            }
        }
    }

    public class MyFiber : FakeFiber
    {

        //recursive loop that never throws stack overflow
        async void DoLoop(int count)
        {
            await Yield(); //clear callstack

            Console.WriteLine("{0} {1}", count, System.Threading.Thread.CurrentThread.ManagedThreadId); 
            
            //we can fetch values from other functions too
            //w/o blowing the call stack
            var i = await IntFunc();
            
            Console.WriteLine("got func result {0}",i);
                     
            if (count == 0)
                return;

            DoLoop(count - 1);
        }

        private async Task<int> IntFunc()
        {
            await Yield(); //clear callstack
            return 1;
        }

        public override void Run()
        {
            DoLoop(100000);
        }
    }

    public abstract class FakeFiber
    {
        public abstract void Run();
        private Task currentTask;
        public bool IsCompleted = false;
        public void Continue()
        {
            var task = currentTask;
            if (task != null)
            {
                task.Start();
                task.Wait();
            }
        }

        protected Task Yield()
        {
            currentTask = new Task(() => { this.currentTask = null; });
            return currentTask;
        }
    }
}

F# style Mailbox / Agent using C# async CTP

Posted on by
Reply

More info on TPL DataFlow can be found here : http://www.microsoft.com/downloads/en/details.aspx?FamilyID=d5b3e1f8-c672-48e8-baf8-94f05b431f5c

Here is a (naive) F# style Mailbox / Agent using the C# async CTP :

    class Program
    {
        static void Main(string[] args)
        {
            var agents = new List<MyAgent>();
            //create 100 000 agents
            for (int i = 0; i < 100000; i++)
                agents.Add(new MyAgent());

            //buffer some messages
            agents.AsParallel().ForAll(a => a.Send(DateTime.Now.ToString()));

            //start agents
            agents.AsParallel().ForAll(a => a.Run());

            //send some more messages
            agents.AsParallel().ForAll(a => a.Send(DateTime.Now.ToString()));

            Console.ReadLine();
        }
    }

    public class MyAgent : Mailbox<string>
    {
        
        public override async void Run()
        {
            while (true)
            {
                var message = await Receive();                
                Console.WriteLine("Agent {0} got {1}",this.Id, message);
            }
        }
    }

    public abstract class Mailbox<T>
    {
        private static int id;

        protected Mailbox()
        {
            this.Id = id++;
        }

        public int Id { get;protected set; }

        BufferBlock<T> buffer = new BufferBlock<T>();

        
        public abstract void Run();
        
        
        public void Send(T message)
        {
            buffer.SendAsync(message);
        }

        protected async Task<T> Receive()
        {
            return await buffer.ReceiveAsync();
        }
    }

This way, we can spawn thousands of agents w/o allocating threads for each of them.
The message loop is executed on the threadpool for each iteration and then suspended untill a new message arrives.

Async CTP first impressions

Posted on by
1

This is just my first observations. nothing fancy..

I’ve just installed the new Async CTP (for C# 5 async features)
The SP1 Refresh can be found here: http://msdn.microsoft.com/sv-se/vstudio/async/

The new async and await features makes async programming so much sweeter, it lets you write async code in a sequential manner.
e.g.

static async void ShowGoogleHtmlCode()
{
  WebClient client = new WebClient();
   var result = await client.DownloadStringTaskAsync("http://www.google.com");
   Console.WriteLine(result);
}

This code looks sequential, but the code will return/yield back to the caller when it hits the “await” keyword.
Once the expression after “await” completes, the code will continue to run.

So far so good.
However, there are some design considerations.

Consider this:

public async void SetupUi()
{
  var blogService = new BlogServiceClient();
     var categories = await blogService.GetCategories();
  var latestPosts = away blogService.GetLatestPosts();

     this.Categories.DataSource = categories;
     this.Posts.DataSource = latestPosts;
}

This code will call GetCategories and GetLatestPosts at the same time and then wait for _both_ of them to complete before continuing to fill the GUI elements.
If you are doing a Silverlight app, then you probably want to display each GUI element as soon as possible, and thus, the above code could be rewritten to:

public async void SetupUi()
{
  SetupCategories();
  SetupPosts();
}

public async void SetupCategories()
{
  var blogService = new BlogServiceClient();
     var categories = await blogService.GetCategories();
     this.Categories.DataSource = categories;
}

public async void SetupPosts()
{
  var blogService = new BlogServiceClient();
  var latestPosts = away blogService.GetLatestPosts();
     this.Posts.DataSource = latestPosts;
}

This way, the async calls will be independent of each other and fill the corresponding GUI element once the data it needs has been fetched.

Also, if you were to write the first code in this way:

public async void SetupUi()
{
  var blogService = new BlogServiceClient();
     var categories = await blogService.GetCategories();
     this.Categories.DataSource = categories;

  var latestPosts = away blogService.GetLatestPosts();
     this.Posts.DataSource = latestPosts;
}

In this case, the call to GetCategories would be invoked, and the code waits for it to complete.
Once the categories have been fetched, the GUI element is filled and _then_ the call to GetLatestPost() would be invoked.
Thus, the async calls would not execute at the same time and the time span for the SetupUI to complete would be the same as if all of it were sync code.

Thats all for now..