python runtime_error ai_generated true

RuntimeError: Cannot create subprocess in event loop that is not running

ID: python/asyncio-cannot-create-subprocess

Also available as: JSON · Markdown · 中文
80%Fix Rate
83%Confidence
0Evidence
2024-08-15First Seen

Version Compatibility

VersionStatusIntroducedDeprecatedNotes
3.8 active — — —
3.9 active — — —
3.10 active — — —

Root Cause

Attempting to create an asyncio subprocess (e.g., via asyncio.create_subprocess_exec) before the event loop is started or after it is stopped.

generic

中文

在事件循环启动前或停止后尝试创建 asyncio 子进程（例如通过 asyncio.create_subprocess_exec）。

Workarounds

  1. 95% success Use asyncio.run() to automatically manage the event loop lifecycle 
    async def main(): proc = await asyncio.create_subprocess_exec('cmd'); asyncio.run(main())
  2. 90% success Ensure the loop is running before creating subprocess 
    loop = asyncio.new_event_loop(); asyncio.set_event_loop(loop); loop.run_until_complete(create_subprocess())

Dead Ends

Common approaches that don't work:

  1. Using asyncio.get_event_loop() to get a loop and then calling run_until_complete 60% fail

    get_event_loop() may return a closed loop; subprocess creation requires a running loop.

  2. Setting the event loop policy to WindowsProactorEventLoopPolicy 40% fail

    This only applies to Windows; the error is about loop state, not platform.