Is it possible to call async function more than once at certain time interval?

[ujur007]

• bleak version:Latest
• Python version:3.8.10
• Operating System: Linux Mint-64bit
• BlueZ version (bluetoothctl -v) in case of Linux: 5.56

Description

I realized that calling the async function more than once or creating two saparate async function gives a runtime error "event loop is already closed". While searching for solution I found the suggestion to move everything with await in one function. While I may want to create another async function or call the same function more than once to see if the device is discover or new devices are available.

[dlech]

There should only ever be one run loop run in your application. Please see the example programs for how to write a program that uses a single call to asyncio.run() to do this.

You can use asyncio.create_task(), asyncio.gather(), asyncio.wait(), etc. to run multiple tasks in parallel.

[ujur007]

Thanks. Do you refer to any specific example in this case? because, I think that most of the examples are pretty basics.
What I want to see is how to wait for some unknown time.

I am actually working on creating an application. The example scenario would be to let's say first check the available devices, then to connect to one of then and then send some values for the characteristics. The delay in this case would be user input based.

[dlech]

What I want to see is how to wait for some unknown time.

This is generally done with asyncio.Event if you don't need to pass any information from the trigger to the waiter or asyncio.Future if you do need to pass a value.

[ujur007]

I tried with asyncio.Event, await, create_task etc but as I am using kivy buttons where a callback must be defined with 'def' syntax only this seems not possible to me. Cause when the awaitables are running everything else just stops.

[dlech]

Can you share a simple reproducible example code?

[ujur007]

Yes, sure. The following is a part of my code where I have tasks running in event loop. The scanview_task does not finish and showrgbmatrix does not run at all. I have to define btn_press methods with def syntax and then wait in other task using either while(variable=True) loop or other methods to wait until task can run till end.

def __init__(self, **kwargs):
     self.disconnect = False
     super(DeviceList,self).__init__(**kwargs)
     self.cols = 2
     asyncio.run(self.scandevices())

 async def scandevices(self):
     self.event = asyncio.Event()
     scan_task = asyncio.create_task(self.scanview_task(self.event))
     await scan_task
     
     self.event2 = asyncio.Event()
     wait_task = asyncio.create_task(self.waiting(self.event2))
     await wait_task
     
 async def scanview_task(self, event):        
     self.searchdevices = await BleakScanner.discover(5)
     for i in self.searchdevices:
         self.connectbutton = Button(text = 'Connect', size_hint =(0.2,0.4), pos_hint = {'center_x' : 0.5, 'center_y':0.5})
         self.address = i.address
         client = BleakClient(self.address)            
         self.connectbutton.bind(on_press = partial(self.showrgbmatrix, client))
         self.label = Label(text = str(i.name + '\n' + i.address + '\n' + str(i.rssi)))
         self.add_widget(self.label)
         self.add_widget(self.connectbutton)

  def showrgbmatrix(self, client, instance):
     self.disconnect = True 
     print("Client...")
     print(client)        
     self.interesting_device = client     
     self.clear_widgets()
     self.colorpicker = ColorPicker()
     self.add_widget(self.colorpicker)
     self.sendbtn = Button(text = 'Send', size_hint=(0.5,0.1))
     self.add_widget(self.sendbtn)
     self.sendbtn.bind(on_press = partial(self.send_rgb_colors, self.interesting_device))

 async def waiting(self, event):
     await asyncio.sleep(3600)

[ujur007]

I think I have got some hints. Instead of running the tasks in one single flow, I can put them inside a While() loop. But not sure that ordinary functions(without async) functions will work. Basically, I need them for the button triggers.
I will check a very simple example and let you know.

[ujur007]

I think that with Kivy it will be difficult to deal with this issue. Because for buttons it needs only non-synchronous def functions. Which will close the event loop or starting again will give error.
Another way is to keep the event loop running but then the button's bind methods will not work.!!

[dlech]

Are you using app.async_run("asyncio") to run the Kivy app? https://kivy.org/doc/master/api-kivy.app.html#asynchronous-app

Anyway, this seems like a discussion for Kivy, not Bleak.

[ujur007]

Yes, but there are issue with kivy asyncio. Anyways will try every possible approach.

[ujur007]

I can confirm that the problem was not with the Bleak but with Kivy's asyncio implementation.
Because, I can run the same code with other GUI platforms.