Blocking call in async (ARCH2028)

Key python.async.blocking-call-in-async · Severity error · Category async

Synchronous blocking calls (time.sleep, blocking IO, sync HTTP/DB drivers) inside an async function stall the event loop and starve all concurrency. Use the asynchronous equivalents instead.

Incorrect

import time

async def poll():
    time.sleep(5)  # blocks the event loop
    return await fetch_status()

Correct

import asyncio

async def poll():
    await asyncio.sleep(5)  # does not block the loop
    return await fetch_status()

Fix

Replace the blocking call with its async equivalent, or offload it to a thread pool via run_in_executor.