Heh, I'm not the only one who always wrote his own async mutex for any non-trivial async codebase.

It may seem like single-threaded execution doesn't need mutexes, but it is a fact that async/await is just another implementation of userspace threads. And like all threads, it may lead to data races if you have yield points (await) inside a critical section.

People may say what they want about bad design and reactive programming, but thread model is inherently easier to reason about.