Coroutines in C (Simon Tatham, 2000)

I've found myself at this webpage multiple times while trying to minimize the complexity of APIs in my C projects. I think it does a lovely job explaining control flow and it has helped me to think more explicitly about storage of state on and off the stack as well as the readability consequences of different approaches. My conclusion for now is that the choice to use C coroutines is best left to the library user. For example: Mongoose (https://github.com/cesanta/mongoose)…

A really good library that we use is libco[0], it supports different architectures and mechanisms. We use it extensively on Fluent Bit[1] to manage async IO network operations (epoll + coroutines). - [0] https://byuu.org/library/libco/ - [1] https://fluentbit.io

This is very nice in theory, but in practice you can only do it in assembly language, because no commonly used high level language supports the coroutine call primitive. This might have been true when the article was written, but things are slightly different today. JavaScript, Python, and C# have picked up generator primitives that can be abused to provide limited coroutine support. Lua, with actual coroutine support, is gaining in popularity. And it will be interesting to see what…

It is a little unfortunate that one of the few (or only) underlying abstraction of the machine that C chose to leave out was that of coroutines. I find this rather ironic because I have been told that PDPs, the virtual machine model that C is based on, had instruction level support for exchanging control very efficiently. I have also heard that VMs like LLVM aren't that good at portably exposing efficient exchange of control between stack frames (please correct…