Question

I’m currently writing an HTTP server in C so that I’ll learn about C, network programming and HTTP. I’ve implemented most of the simple stuff, but I’m only handling one connection at a time. Currently, I’m thinking about how to efficiently add multitasking to my project. Here are some of the options I thought about:

1. Use one thread per connection. Simple but can’t handle many connections.
2. Use non-blocking API calls only and handle everything in one thread. Sounds interesting but using select()s and such excessively is said to be quite slow.
3. Some other multithreading model, e.g. something complex like lighttpd uses. (Probably) the best solution, but (probably) too difficult to implement.

Any thoughts on this?

Answer 1

There is no single best model for writing multi-tasked network servers. Different platforms have different solutions for high performance (I/O completion ports, epoll, kqueues). Be careful about going for maximum portability: some features are mimicked on other platforms (i.e. select() is available on Windows) and yield very poor performance because they are simply mapped onto some other native model.

Also, there are other models not covered in your list. In particular, the classic UNIX “pre-fork” model.

In all cases, use any form of asynchronous I/O when available. If it isn’t, look into non-blocking synchronous I/O. Design your HTTP library around asynchronous streaming of data, but keep the I/O bit out of it. This is much harder than it sounds. It usually implies writing state machines for your protocol interpreter.

That last bit is most important because it will allow you to experiment with different representations. It might even allow you to write a compact core for each platform local, high-performance tools and swap this core from one platform to the other.