Cancel Async Tasks

Overview

This skill provides guidance for implementing robust asyncio task cancellation in Python, particularly when dealing with signal handling (SIGINT/KeyboardInterrupt), semaphore-based concurrency limiting, and ensuring proper cleanup of all tasks including those waiting in queues.

Key Concepts

Signal Propagation in Asyncio

Understanding how signals interact with asyncio is critical:

1. KeyboardInterrupt vs CancelledError: When SIGINT is received during asyncio.run(), the behavior differs from catching exceptions inside async code. The event loop typically converts the interrupt to CancelledError that propagates through tasks.

2. Signal handler context: Signal handlers run in the main thread, but asyncio tasks may be in various states (running, waiting on semaphore, waiting on I/O).

3. Event loop state: The event loop's handling of SIGINT depends on whether it's running asyncio.run() vs manual loop management.

Task Lifecycle States