python runtime_error ai_generated true

RuntimeError: asyncio.run() cannot be called from a running event loop

ID: python/starlette-loop-already-running

Also available as: JSON · Markdown · 中文
80%Fix Rate
87%Confidence
0Evidence
2024-04-21First Seen

Version Compatibility

VersionStatusIntroducedDeprecatedNotes
0.27+ active — — —

Root Cause

A synchronous FastAPI/Starlette route or dependency called asyncio.run() while the server's event loop was already running.

generic

中文

同步的 FastAPI/Starlette 路由或依赖项在服务器事件循环已运行时调用了 asyncio.run()。

Workarounds

  1. 95% success 
    @app.get('/x')
async def handler():
    return await some_coroutine()
  2. 75% success 
    import anyio
result = anyio.from_thread.run(some_coroutine)

Dead Ends

Common approaches that don't work:

  1. 70% fail

    Patches the loop but breaks uvicorn's task scheduling and can deadlock under load.

  2. 85% fail

    Raises 'This event loop is already running' since the loop cannot be re-entered.