Asyncio.get_event_loop does not work with fsspec.asyn.sync

[omerXfaruq]

Hello, the example below does not work, while I believe it should work.

import asyncio
import fsspec.asyn

print("yey")
loop = asyncio.get_event_loop()
fsspec.asyn.sync(loop, asyncio.sleep, delay=5)
print("yey")

After printing out the first "yey" the program does not output anything, and when it is stopped, it outputs this:

yey
Traceback (most recent call last):
  File "F:\SecondaryDownloads\git_repos\gradio\dev_mode.py", line 7, in <module>
    print("yey")
  File "F:\SecondaryDownloads\git_repos\gradio\venv\lib\site-packages\fsspec\asyn.py", line 54, in sync
    if event.wait(1):
  File "C:\Program Files\WindowsApps\PythonSoftwareFoundation.Python.3.9_3.9.2800.0_x64__qbz5n2kfra8p0\lib\threading.py", line 574, in wait
    signaled = self._cond.wait(timeout)
  File "C:\Program Files\WindowsApps\PythonSoftwareFoundation.Python.3.9_3.9.2800.0_x64__qbz5n2kfra8p0\lib\threading.py", line 316, in wait
    gotit = waiter.acquire(True, timeout)
KeyboardInterrupt

However, it works perfectly when fsspec.asyn.get_loop is used.

import asyncio
import fsspec.asyn

print("yey")
loop = fsspec.asyn.get_loop()
fsspec.asyn.sync(loop, asyncio.sleep, delay=5)
print("yey")

[omerXfaruq]

I am unsure why it does not raise an error, and waits indefinitely. It should raise an error according to this line

[martindurant]

You are not calling sync from within a loop, you are calling sync with a loop in the same thread, and then blocking waiting on a thread event to be set. The event wait and the event loop cannot progress at the same time, so you deadlock.

[omerXfaruq]

Then what about this situation, is it still not from a loop?

from fastapi import FastAPI

app = FastAPI()


@app.get("/")
async def main():
    import asyncio
    import fsspec.asyn
    print("yey")
    print(asyncio.get_running_loop())
    loop = asyncio.get_event_loop()
    fsspec.asyn.sync(loop, asyncio.sleep, delay=5)
    print("yey")

[martindurant]

Ah, well if you are in a loop already, you should not be using sync at all. All async backends offer async versions of their methods, and you would simply await them.

[omerXfaruq]

Ah, well if you are in a loop already, you should not be using sync at all. All async backends offer async versions of their methods, and you would simply await them.

Well, this is actually a use-case that is missing in python. For example in Gradio we allow users to launch the server in sync functions for ease of use, and later need async calls.

[graingert]

asyncio.get_event_loop() is being made an alias of asyncio.get_running_loop() on python 3.12