Cloud Functions python37: Future attached to a different loop

[bryzgaloff]

I decided to create the issue in the docs repo. However, I don't know whether it is a right place to state the issue. Please point me to a correct place if it is needed.

Good news: python37 runtime environment allows to define handler as async def. This is a huge advantage versus sync-only handlers of AWS, for example.

Bad news: however, the handler is called using asyncio.run. This could be investigated from the traceback in case of exception: File \"/function/runtime/runtime.py\", line 157, in handle_event\n result = asyncio.run(result). This causes RuntimeError of Task … got Future … attached to a different loop if any of the resources are created outside the function (which is a common case for initialising a database connection) since asyncio.run creates a new loop.

Example code:

import aioch

ch = aioch.Client(…)  # attached to an initially created loop

async def echo(event, ctx):
    await ch.execute('SELECT 1')  # RuntimeError

Response:

{
    "errorMessage": "Task <Task pending coro=<echo() running at /function/code/index.py:16> cb=[_run_until_complete_cb() at /function/runtime/lib/python3.7/asyncio/base_events.py:157]> got Future <Future pending cb=[_chain_future.<locals>._call_check_cancel() at /function/runtime/lib/python3.7/asyncio/futures.py:351]> attached to a different loop",
    "errorType": "RuntimeError",
    "stackTrace": [
        "  File \"/function/runtime/runtime.py\", line 157, in handle_event\n    result = asyncio.run(result)\n",
        "  File \"/function/runtime/lib/python3.7/asyncio/runners.py\", line 43, in run\n    return loop.run_until_complete(main)\n",
        "  File \"/function/runtime/lib/python3.7/asyncio/base_events.py\", line 583, in run_until_complete\n    return future.result()\n",
        "  File \"/function/code/index.py\", line 16, in echo\n    await ch.execute('SELECT 1')\n",
        "  File \"/function/code/aioch/client.py\", line 38, in execute\n    **kwargs)\n"
    ]
}

The proper way to call async serverless functions handlers is asyncio.get_event_loop().run_until_complete(result) which preserves the initially created event loop. Please see a more detailed explanation in my Stack Overflow answer for Amazon Web Services.

Could you please provide any expectations on whether it will be fixed and when? Thank you in advance.

[myusosnovskay]

Здравствуйте!

Вы можете попробовать протестировать новое поведение, использовав environment-переменную PYTHON_ASYNCIO_SAFE и присвоив ей значение True.