RuntimeError when using the latest uvloop

[tjkemp]

Description

Ray fails with a RuntimeError when using the latest uvloop version.

Expected Behavior

The script should execute successfully without any RuntimeError.
The same example works with earlier uvloop versions (uvloop==0.21.0).

Observed Behavior

The script fails with:

RuntimeError: There is no current event loop in thread 'MainThread'.

Notes

• Related issue asyncio.get_event_loop raises error instead of spawning new loop when no loop is running. MagicStack/uvloop#702

Versions / Dependencies

ray==2.50.1
vllm==0.11.1rc2
uvloop==0.22.1

Reproduction script

1. Start a Docker container, for example rocm/vllm:rocm6.4.1_vllm_0.10.1_20250909
2. Install the latest uvloop: pip install uvloop==0.22.1
3. Download and run the Ray LLM example: curl -O https://raw.githubusercontent.com/ray-project/ray/9746a94393de8cf331e1906541a1df002072dad2/doc/source/data/doc_code/working-with-llms/basic_llm_example.py
4. Run the example: python basic_llm_example.py

Issue Severity

None

[jjyao]

@tjkemp if I understand correctly, it's a uvloop bug and the fix should be on their side?

[sepastian]

I ran into the same error trying the batch inference example locally, in Jupyter.

Workaround: Downgrading to uvloop==0.21.0 solves the problem, as suggested elsewhere,

uv pip install uvloop==0.21.0

Don't forget to restart the Jupyter kernel.

---

On a sidenote, the example I tried to run requires to install vllm==0.7.2, which is quite of of date. I ran into other issues and had to use the latest vllm==0.11.0 at the time of writing. Thus, I fixed my packages running:

uv pip install -U vllm uvloop==0.21.0

[han-steve]

Same here, running ray==2.52.0 and vllm==0.11.1. Downgrading to uvloop==0.21.0 worked.