GetCharacteristicsAsync function gets stuck in Windows 11 while discovering characteristics of Bluetooth Low Energy devices

Question

Hello,
Context:
I have a code snippet that discovers Bluetooth Low Energy device characteristics using GetCharacteristicsAsync function. I am storing the async process returned by this function and waiting for it to be over to obtain the result.

Issue:
This is working fine in Windows 10 but in Windows 11 the async process gets stuck and never finishes execution. I generally use the Uncached mode but I have tried both Cached and Uncached in Windows 11 and it didn't help.

Query:
Is this a known issue in UWP BLE library in Windows 11 and more importantly how do I workaround this? If anybody has useful experience/input relating to this issue it would be much appreciated.

Answer 1

Hello!
I have the same problem. Sometimes GetCharacteristicsAsync does not return calling something like this:

CancellationTokenSource cts = new CancellationTokenSource();
cts.CancelAfter(TimeSpan.FromSeconds(5));
await service.service.GetCharacteristicsAsync(BluetoothCacheMode.Uncached).AsTask<GattCharacteristicsResult>(cts.Token);

If I pause execution I see that this task is scheduled but not started yet since way over 15 seconds.
It seems that this is happening if I try to reconnect to a device which had a power cycle so connection was aborted before.

Is there some news on this?

Answer 2

In our case it does not get stuck but the status is access denied.

auto chars = s.GetCharacteristicsAsync(BluetoothCacheMode::Uncached).get();  
GattCommunicationStatus status = chars.Status();  
  

Status gets set to GattCommunicationStatus::AccessDenied

Same laptop (Dell XPS 15), Windows 10 no problem, only Windows 11

Answer 3

This could be related to your situation:
https://developercommunity.visualstudio.com/t/ble-using-winrt-access-denied-when-executing-getch/1703310

[Possible solution at the last EDIT]

But it can be altogether a different thing.
In my case (using Windows 10, but not an UWP application, calling WinRT libs) this happens:
Only the first call gives me the attributes, then "Access Denied".
After some time a single call will give a valid answer again, but it's pretty rare (in one case after 52 seconds, in another 21 seconds).

In this case I will try to make a solution when everytime I'm asking for data, I will build the BLE from ground up (device detection, looking for correct device, getting attributes), get the data and then destroy everything, then do it again everytime I need data from a device.
This feels very wrong and could lead to more problems.
The reasoning behind this that the first time I collect information, everything is accessible.

Hope this helps someone.

EDIT1: This is not the case for every Characteristics! For example.: "Battery Level" works every time, but some other characteristics have this behaviour (but only on Windows devices, an Android phone or tablet works everytime, with every characteristic).

EDIT2: The problem is at a deeper level. Rebuilding the connection from zero each time does not solve the problem. The second time I still can't have the data. But with every program start it works.

EDIT3: SOLUTION!
Dispose is the key! After the first request you have to Dispose both the BluetoothLEDevice and the GattDeviceService you get while connecting! The system thinks it is still inuse!