Writing a highly scalable TCP/IP server in C# 5 with the async/await pattern?

Question

I'm tasked with designing a fairly simple TCP/IP server that must accept connections from multiple clients. It needs to be written in C#, and I'm using .NET 4.5. That said, I'm not sure what is the current "state of the art" for TCP/IP server/client scalability in .NET 4.5.

I did see this post: How to write a scalable Tcp/Ip based server. But that relates to .NET 2.0 and 3.5 and makes no mention of the async/await pattern.

I am capable of writing a server the "old way"... but I want to know what the "new way" is.

• What is the best way to use the new Async methods on Socket, TcpClient or TcpListener to create a scalable server in C#?
• Do the new Async methods leverage I/O Completion Ports?
• Is rolling your own Socket listener more efficient, or are the TcpListener/TcpClient classes pretty good now?

EDIT: Additional questions.

Answer 1

What is the best way to use the new Async methods on Socket, TcpClient or TcpListener to create a scalable server in C#?

There aren't any new async methods on Socket; the methods named *Async on Socket are a special set of APIs to reduce memory usage. TcpClient and TcpListener did get some new async methods.

If you want the best scalability, you're probably best using Stephen Toub's custom awaiters for Socket. If you want the easiest to code, you're probably better off using TcpClient and TcpListener.

Do the new Async methods leverage I/O Completion Ports?

Yes, just like most of the other asynchronous APIs in the BCL. AFAIK, the Stream class is the only one that may possibly not use the IOCP; all other *Begin/*End/*Async methods use the IOCP.

Is rolling your own Socket listener more efficient, or are the TcpListener/TcpClient classes pretty good now?

The classes are pretty good as they are. Stephen Toub has a blog post that is a bit more efficient in terms of memory use.