Async IO with epoll, io_uring, and C++ coroutines

• Introduction
• Project setup
• Errors
• File descriptors and sockets
• HTTP client interface and buffers
• Blocking HTTP client
• Epoll HTTP client
• io_uring
• io_uring HTTP client
• io_uring with "manual" state machine
• Coroutines
  • Coroutine API
  • An async coroutine type (Z)
  • Coroutine handle awaiter
• io_uring event loop with coroutines
• HTTP client with io_uring and coroutines
• Combining coroutines

Introduction

Why does the C++ coroutine API look the way it does? This was the main question on my mind when I started the explorations documented in this post. Most C++ coroutine explanations focus on the mechanics of the API, the many customization points, and maybe a few examples. This post approaches C++ coroutines from one of its motivating use cases: concurrent IO with event loops. I find that it's much…