shinyorg / shiny

Component/Nuget

GPS or Geofencing (Shiny.Locations)

What operating system(s) are effected?

iOS (13+ supported)
Mac Catalyst
Android (8+ supported)
Windows (.NET 7 Target - only Core is currently supported, BLE is coming)

Version(s) of Operation Systems

Any

Hosting Model

MAUI
Native/Classic Xamarin
Manual

Steps To Reproduce

Invoke IGpsManager.GetCurrentPosition() from two threads.

Expected Behavior

Invoking static IObservable<GpsReading> GetCurrentPosition(this IGpsManager gpsManager) yiels a location or throws an exception. It does this by possibly starting the gps listener, and then stopping the listener once finished.

Actual Behavior

Despite the use of a semaphore a race condition appears to be possible: by looking at the code it seems like it releases the semaphore before stopping the GPS manager, meaning a second thread can invoke GetCurrentPosition() as well, starting the GPS manager, only for the first thread to continue with stopping the listener.

I think the semaphore should only be released after the gps manager is stopped.

Extension method here:

shiny/src/Shiny.Locations/Extensions.cs

Line 59 in 9d09a0a

    
           public static IObservable<GpsReading> GetCurrentPosition(this IGpsManager gpsManager) => Observable.FromAsync(async ct =>

            ...
        }
        finally
        {
            currentLocSemaphore.Release();
            if (iStarted)
                await gpsManager.StopListener().ConfigureAwait(false);
        }

If I'm mistaken, I'm happy to hear why.

Exception or Log output

No response

Code Sample