San Diego C++ Meetup Jan 17 2023 – Coroutines

Hello everyone!

On Tuesday, Jan 17 2023 we hosted the 46th session of San Diego C++ Meetup.

This time, I gave a talk on C++20 Coroutines which I named “YACRT – Yet Another Coroutine Talk”. There are many good talks out there and I decided to have another one for the San Diego C++ group.

Here is the recording:

During the talk, I’ve described both Generators and non-Generators techniques, focusing on thread context, the C++20 Coroutine API and the various customization points. I had few CLion gdb/debugger screenshots to demonstrate the various parts of the runtime call flow.

Generators – I showed simple Generator with co_yield.

For non-generators, I was inspired by this blog post Pablo A io_uring and coroutine post which has 3 parts. It talks about the combination of Coroutines and Linux 5.x Kernel’s io_uring feature which is by itself really cool feature to be aware of. Here is a simple diagram. You basically submit work (read/write from/to FD) and the kernel is doing it on your behalf! You just query for completion and carry-on.

And what did I implemented for this session? A Coroutine function that is reading bytes from a UDP socket on a dedicated thread once we are suspending an Awaiter, when done – resuming the coroutine and then submitting a request to the kernel for file write. That’s the second co_await/Awaiter. The resume of this co_await happens in main function where we wait on the Kernel operation completion using a blocked function API. Here is a simple diagram of the main parts:

Obviously, you’d need to watch the recording in order to get the full sense of what’s happening.

It was the first time for me presenting on C++20 coroutine and it’s not easy. Lots of moving parts and details to be aware of. It took me 2 hours to go over 60 slides!

Thanks for reading!

Kobi