Single Thread Asynchronous Runtime

This is a simple runtime for std Futures, single thread only.

Intended usage is small workloads ; for example small desktop daemons having multiple IO sources. The goal is to provide an alternative to a loop with select() with a much nicer API and semantics.

This supports only unix targets due to use of poll, RawFd and libc.

Motivation / technical

This has been built mainly for personnal uses and to discover the Rust async ecosystem, in details.

It is designed with low overhead in mind:

• no Arc/Mutex or atomics due to single thread.
• no thread stacks.
• very few memory allocations.
• low dependency count (mostly libc).

Structural pinning : One of the goal was to minimize dependencies for low compile-time overhead. I tried to avoid using any proc_macro dependent crate. However handling structural pinning is very tedious to do manually, and requires many uses of unsafe. In the end I gave in and used pin-project ; this also improves code documentation by having a clear #[pin] tag instead of doc + unsafe impls. The recent pin-project-lite was tried, but it does not support enums nor docstrings in structs.

Interesting points / features

• Tasks use a single allocation (including the Waker).
• Task frame use trait objects for type erasure, avoiding using unsafe.
• JoinHandle<T> is a nice API, taken from async-task.
• uses poll, so async File IO should be possible.
• A very minimal API for interacting with events (reactor) : a pair of runtime-specific Future types that complete on event trigger.
• Use of an intrusive list design -> those future types require no memory allocation (in place).

Unsafe usage

• Building a Waker with the vtable. Tedious to do. Unavoidable in my case, as I cannot use the From<Arc<W>> where W : Wake.
• PinWeak<T> : missing support for creating Pin<Weak<T>> from Pin<Rc<T>>.
• PinCell<T> : a RefCell like structure propagating pinning.
• Wrapper to poll() syscall.
• The internal intrusive list, which in my opinion is the least robust unsafe use.

TODO

Test with applications : xstalker, ...