Bleak and Applications with GUI

• bleak version: 0.7.1
• Python version: 3.8
• Operating System: macOS Catalina 10.15.6

Description

So before anything, I know that this “issue” that I am writing is not actually Bleak’s issue/bug. It is more of a question than a bug report. In summary, I want to use Bleak in an application that has a graphical user interface and I am having issues with the asynchronous nature of Bleak. I explained the steps I’ve taken and the errors I faced in detail below:

What I Did

Since I already had a GUI written in Kivy, I tried to use Bleak and integrate it into the Kivy’s Button callbacks.

For the search (discovery) part, I wrote async def search_for_bles() in which I call await discover(). To call this function from the button’s callback I had to use asyncio.run() method, which worked fine!

I used the same strategy (await, async def, and asyncio.run) connect(), here is a part of the code (I removed the pointless lines)

def connect_btn_callback(self,......):

    self.ble_obj=BLE(found_client, ...... )

    asyncio.run(self.ble_obj.connect()) # [1] Works fine.    
    asyncio.run(self.ble_obj.ask_control()) # [2] Runtime Error: 'Event loop is closed'

in the BLE class:

def __init__ (self, client, .....):
    self.client=client
    ....

async def connect (self):
    await self.client.connect() # [3] works fine
    await self.ask_control() # [4] works fine

async def ask_control(self):
    await self.client.write_gatt_char(constants.CONTROL_HANDLE, bytearray([0x02, 0x73, 0x0a]), False)

The comments in the code are showing where the error occurs (this also happens for the disconnect, and other methods)

What is interesting for me is that the ask_control inside [1], i.e. [4], works without an issue (this means that the ask_control function is healthy). However, [2] gives me an error, RunTime error: 'event loop is closed'

Other things that I have tried:

After a few days working on these issues full-time, I found many related issues but none of the solutions worked:

1. from asgiref.sync import async_to_sync
2. Using loop=asyncio.get_event_loop()
3. Using loop=asyncio.get_running_loop()
4. Using loop=asyncio.new_event_loop and asyncio.set_event_loop(loop)
5. Using nest_asyncio

What I am asking

So I am presenting this issue to you not (specifically) as the developers of Bleak, but as experienced python users/developers. I want to have Bleak and a cross-platform GUI in one app. Even if you think that using another GUI makes using Bleak easier, please let me know.

Thank you.

[bardiabarabadi]

Thank you, @hbldh for your response. So the reason I didn’t use async_run() (Kivy) was that it was only available on the rc versions (not the stable 1.11.1). Anyway, I updated Kivy to 2.0.0rc3 and tried running the Bleak functions using loop=asyncio.get_event_loop() and loop.run_until_complete. Of course, another problem arose; apparently run_until_complete closes the loop after the future function returns, and because the loop is shared with UI, the applictation crashes.

For future reference: the issue can be solved by having these two lines at the beginning of the code:

import nest_asyncio
nest_asyncio.apply()

Thank you for answering my question, everything is working fine now. I am closing this thread.

P.S. @Carglglz Thanks for your comment. As I mentioned in the “Other things that I have tried” section of my initial post, getting the currently running loop (with asyncio.get_event_loop()) gave me the same error. The reason is that the Kivy does not lwt go of the running thread and thus there is not any event loop for asyncio to extract.

[Carglglz]

@bardiabarabadi

The comments in the code are showing where the error occurs (this also happens for the disconnect, and other methods) What is interesting for me is that the ask_control inside [1], i.e. [4], works without an issue (this means that the ask_control function is healthy). However, [2] gives me an error, RunTime error: ‘event loop is closed’

The reason for this is explained in the asyncio.run docstring. The important part:

This function always creates a new event loop and closes it at the end.
It should be used as a main entry point for asyncio programs, and should
ideally only be called once.

(do help(asyncio.run) to see the complete version)

So I use loop.run_until_complete instead and it works great. (at least with PyQt5) 👍