Streaming is blocking and cannot be cancelled

[varunursekar]

Describe the bug

RunResultStreamed.stream_events() cannot be cancelled using asyncio primitives. In the script below, we'd like to time out if a streaming event takes longer than 5 seconds to arrive. However, using asyncio.wait_for's cancellation event is not propagated to the stream_events iterator.

Debug information

• Agents SDK version: (e.g. v0.0.3)
• Python version (e.g. Python 3.10)

Repro steps

from agents import Agent, Runner, function_tool
import asyncio
import datetime


@function_tool
async def get_secret_key():
    await asyncio.sleep(120)
    return "secret_key"


async def main():
    agent = Agent(
        name="secret_key_agent",
        model="gpt-4.1-mini",
        tools=[get_secret_key],
    )

    result = Runner.run_streamed(agent, input="What is the secret key?")
    event_iter = aiter(result.stream_events())

    while True:
        try:
            event = await asyncio.wait_for(anext(event_iter), timeout=5)
            print(datetime.datetime.now(), event)
        except StopAsyncIteration:
            break
        except asyncio.TimeoutError:
            print("Timed out waiting for next event")
            break  # or continue if you want to keep waiting

if __name__ == "__main__":
    asyncio.run(main())

Expected behavior

The iterator should respond as expected to asyncio cancellations. The loop above should time out.

[ihower]

@varunursekar I’m not sure whether this is a bug or expected behavior, but currently if the caller times out, the SDK won’t cancel streaming immediately. It “safely” waits for any background task to finish (see _await_task_safely function).

If you need streaming timeouts today, the best approach seems to be implementing your own timer and call result.cancel() directly. It supports "immediate" and "after_turn". See: #1896 and #1895

[seratch]

This use case was not supported by design, but enabling to use the timeout this way may be useful for other developers too. My pull request #2226 may resolve it. Feedback is welcome!