Asyncio: A library with too many sharp corners
9 months ago
- #asyncio
- #concurrency
- #python
- asyncio was introduced in Python 3.4 and became non-provisional in Python 3.5, adding async/await keywords.
- asyncio has significant design flaws, including broken cancellation, task destruction issues, and problematic I/O handling.
- Cancellation in asyncio is edge-triggered, leading to potential deadlocks and swallowed cancellations, unlike Trio's level-triggered approach.
- asyncio does not keep strong references to tasks, causing tasks to be garbage collected mid-execution, leading to warnings like 'Task was destroyed but it is pending!'.
- asyncio's I/O handling is callback-based and non-linear, making it harder to use compared to Trio's straightforward socket API.
- asyncio.Queue lacks proper backpressure mechanisms and can lead to memory leaks or deadlocks if not managed carefully.
- Trio and AnyIO offer better alternatives with structured concurrency, level-triggered cancellations, and more intuitive APIs.
- Other minor issues include poor thread integration, signal handling, and task group cancellation problems in asyncio.