It is not possible to use synchronous and asynchronous calls together

[vovochka404]

ls = fs.ls("/path")
f = await fs.open_async("/path/file1")
data = await f.read()

Will lead to:

Task <Task pending name='Task-1' coro=<main() running at /.../test.py:100> cb=[_run_until_complete_cb() at /opt/homebrew/Cellar/python@3.9/3.9. 17/Frameworks/Python.framework/Versions/3.9/lib/python3.9/asyncio/base_events.py:184]> got Future <Future pending cb=[shield.<locals>._outer_done_callback() at /opt/homebrew/ Cellar/python@3.9/3.9.17/Frameworks/Python.framework/Versions/3.9/lib/python3.9/asyncio/tasks.py:907]> attached to a different loop

The exception occurs here: aiohttp/connector.py:1145

The problem arises due to the use of the same session within which the aiohttp.TCPConnector is saved, which upon creation receives the current event_loop.
But synchronous and asynchronous requests are executed in different event_loops. And if the current event_loop does not match what it was when aiohttp.TCPConnector was created, we always get an exception.

The simplest solution is to set refresh to True in s3fs.core.S3FileSystem.set_session, but it seems that this is not the best solution.

[martindurant]

Yes, you are completely right: it is expected that the event loop is either in the same thread as the execution (in which case you use the async methods) or not (in which case you don't). The argument asynchronous= can be used to make this difference, as it will bust the caching mechanism; originally this argument made a real difference, but that difference has shrunk to nothing.

The simplest solution is to set refresh to True in s3fs.core.S3FileSystem.set_session

You should create two S3FileSystem instances, one in a coroutine for use with async, and one outside.

[vovochka404]

May be we can have sync/async session inside one fs instance?

[martindurant]

The session is always async, so that you can do bulk operations even in sync code. The difference is where the event loop is running, so trying to maintain multiple loops running in different threads within the one instance seems to me to be a bad idea.