Methodologies to handling multiple clients in C++ winsock

Question

I'm developing a peer to peer message parsing application. So one peer may need to handle many clients. And also there is a possibility to send and receive large data (~20 MB data as one message). There can be situations like many peers send large data to the same peer. I heard there are many solutions to handle these kind of a situation.

• Use thread per peer
• Using a loop to go through the peers and if there are data we can recive
• Using select function
• etc.

What is the most suitable methodology or most common and accepted way to handle these kind of a situation? Any advice or hint are welcome.

Updated: Is there a good peer to peer distributed computing library or framework for C++ on windows platform

Answer 1

Don't use a thread per peer; past the number of processors, additional threads is likely only to hurt performance. You'd also have been expected to tweak the dwStackSize so that 1000 idle peers doesn't cost you 1000MB of RAM.

You can use a thread-pool (X threads handling Y sockets) to get a performance boost (or, ideally, IO Completion Ports), but this tends to work incredibly well for certain kinds of applications, and not at all for other kinds of applications. Unless you're certain that yours is suited for this, I wouldn't justify taking the risk.

It's entirely permissible to use a single thread and poll/send from a large quantity of sockets. I don't know precisely when large would have a concernable overhead, but I'd (conservatively) ballpark it somewhere between 2k-5k sockets (on below average hardware).

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The workaround for WSAEWOULDBLOCK is to have a std::queue<BYTE> of bytes (not a queue of "packet objects") for each socket in your application (you populate this queue with the data you want to send), and have a single background-thread whose sole purpose is to drain the queues into the respective socket send (X bytes at a time); you can use blocking socket for this now (since it's a background-worker), but if you do use a non-blocking socket and get WSAEWOULDBLOCK you can just keep trying to drain the queue (here it won't obstruct the flow of your application).

Answer 2

You could use libtorrent.org which is built on top of boost (boost-asio ). It's focusing on efficiency and scalability.

I have not much experience in developing a socket in C++ but in C# I had really good experience accepting connections asynchronously and pass them to an own thread from a threadpool.