Convert APM Iterative calls to TAP

Question

Since MS had said that both APM and EAP are outdated, TAP is the recommended approach to asynchronous programming in the .NET Framework. Then I want to convert my code from APM to TAP:

public class RpcHelper
{
    public void DoReadViaApm(IRpc rpc, BlockingCollection<ArraySegment<byte>> bc)
    {
        byte[] buf = new byte[4096];
        rpc.BeginRead(buf, 0, buf.Length,
            ar =>
            {
                IRpc state = (IRpc) ar.AsyncState;
                try
                {
                    int nb = state.EndRead(ar);
                    if (nb > 0)
                    {
                        bc.Add(new ArraySegment<byte>(buf, 0, nb));
                    }
                }
                catch (Exception ignored)
                {
                }
                finally
                {
                    DoReadViaApm(state, bc);
                }
            }, 
            rpc);
    }

    public void DoReadViaTap(IRpc rpc, BlockingCollection<ArraySegment<byte>> bc)
    {
        Task.Factory.StartNew(() =>
        {
            while (true)
            {
                Task<byte[]> task = rpc.ReadAsync();
                try
                {
                    task.Wait(-1);
                    if (task.Result != null && task.Result.Length > 0)
                    {
                        bc.Add(new ArraySegment<byte>(task.Result));
                    }
                }
                catch (Exception ignored)
                {
                }
            }
        }, TaskCreationOptions.LongRunning);
    }
}

public interface IRpc
{
    IAsyncResult BeginRead(byte[] buffer, int offset, int size, AsyncCallback callback, Object state);
    int EndRead(IAsyncResult asyncResult);

    Task<byte[]> ReadAsync();
}

The TAP method DoReadViaTap() use TaskCreationOptions.LongRunning, it looks very ugly. Can I make DoReadViaTap() looks better like DoReadViaApm() ?

score 0 · Answer 1 · answered Mar 07 '16 at 15:15

0

I am not entirely sure what your code is supposed to do, but I guess it's some worker waiting for input? You could simplify it by using await and make the started operation asynchronous. Be aware that a task has a timeout, so you might want to set that appropriately or catch the exception.

public void DoReadViaTap(IRpc rpc, BlockingCollection<ArraySegment<byte>> bc)
{
    Task.Factory.StartNew(async () =>
    {
        while (true)
        {
            byte[] result = await rpc.ReadAsync();
            if (result.Length > 0)
            {
                bc.Add(new ArraySegment<byte>(result));
            }
            catch (AggregateException ignored)
            {
            }
        }
    }, TaskCreationOptions.LongRunning);
}

answered Mar 07 '16 at 15:15

Benji Wa

147
7

You code looks better, but not what I expected. I want to kill the long running task, because DoReadViaApm() only use IO thread shortly. – Cauchy Song Mar 08 '16 at 03:23
You mean the task created by `Task.Factory.StartNew()`? You could use a cancellation token to check if that task is supposed to be cancelled. [Example](http://stackoverflow.com/a/19932396/2300387) – Benji Wa Mar 08 '16 at 14:45
Where did the `try` go? The `catch` won't compile without it. – svick Mar 09 '16 at 00:02

score 0 · Answer 2 · answered Mar 09 '16 at 00:01

What you should do is to use async-await. And when you do that, you don't need to start a Task:

public async Task DoReadViaTap(IRpc rpc, BlockingCollection<ArraySegment<byte>> bc)
{
    while (true)
    {
        try
        {
            byte[] result = await rpc.ReadAsync().ConfigureAwait(false);
            if (result != null && result.Length > 0) // or result?.Length > 0 on C# 6
            {
                bc.Add(new ArraySegment<byte>(result));
            }
        }
        catch (Exception ignored)
        {
        }
    }
}

To me, this reads much better than the APM version.

Note that I don't think completely ignoring exceptions and infinite loops with no way to end them are good practices, I just copied those from your code.

I'm looks for a infinite chained task construction: start: Task task = rpc.ReadAsync(); task.ContinueWith { bc.Add(new ArraySegment(result)); goto start: } — Cauchy Song, Mar 09 '16 at 10:11
@CauchySong Why? It's going to be more messy than using `async`-`await`, just like like your APM code. — svick, Mar 09 '16 at 11:19

Convert APM Iterative calls to TAP

2 Answers2