"Minimum" Async Runtime

Take it easy! Asynchronous programming in Rust is actually easy to understand once you get a sense of its philosophy. This repository is used for educational purposes and demonstrates how to build a minimal async runtime from scratch for Rust.

Usage

git clone https://github.com/cubicYYY/minimum-async-runtime-rs.git
cd minimum-async-runtime-rs

Then:

RUST_LOG=INFO cargo run
# For Windows: 
# cmd /V /C "set RUST_LOG=INFO && cargo run"

Overview

The executor is designed to schedule and run tasks asynchronously in a single-threaded environment, but you can modify it for a multi-threaded model easily. It uses a task queue and a signaling mechanism to manage task execution and ensure that tasks are processed in order.

Key Components

• SignalReactor: A simple signaling mechanism using an atomic boolean for task notification. In a real-world async runtime framework, a reactor is responsible for interacting with the kernel and "waking" the corresponding task. Waking a task involves putting the task somewhere the executor will find it and execute it.
• Task: A wrapper around a Future with no return value, allowing it to be scheduled and executed by the executor. It can be tricky to spawn a task with a return value. For more details, refer to tokio and async-std to check their implementation (JoinHandle and type erasure).
• Executor Queue: Consists of tasks that are ready to be polled, applying a simple FIFO scheduling policy to tasks in this simple runtime. In a real-world async runtime framework, additional technical details are introduced to prevent task starvation, but the basic idea is the same.

Code Structure

• SignalReactor: Provides methods to notify and wait for signals.
• Task: Contains the future to be executed and the signal reactor. Implements the Wake trait for scheduling.
• TimerFuture: An example to show how sleep function works in an async runtime.
• spawn: Spawns a new task and adds it to the executor queue.
• block_on: Blocks the current thread until the given future completes, polling tasks in the executor queue.