Update ICameraProvider, Use SemaphoreSlim in CameraProvider to avoid async/await race conditions, Implement IDisplosable

Author: TheCodeTraveler

samples/CommunityToolkit.Maui.Sample/ViewModels/Views/CameraView/CameraViewViewModel.cs

@@ -42,12 +42,15 @@ public partial class CameraViewViewModel(ICameraProvider cameraProvider) : BaseV
 	[ObservableProperty]
 	public partial string ResolutionText { get; set; } = string.Empty;
 
-	public async Task InitializeAsync()
+	public async ValueTask InitializeAsync()
 	{
-		await cameraProvider.InitializeAsync(CancellationToken.None);
-		foreach (var camera in cameraProvider.AvailableCameras ?? [])
+		if (!cameraProvider.IsInitialized)
 		{
-			Cameras.Add(camera);
+			await cameraProvider.InitializeAsync(CancellationToken.None);
+			foreach (var camera in cameraProvider.AvailableCameras ?? [])
+			{
+				Cameras.Add(camera);
+			}
 		}
 	}
 

src/CommunityToolkit.Maui.Camera/Interfaces/ICameraProvider.shared.cs

@@ -14,19 +14,19 @@ public interface ICameraProvider
 	/// List is initialized using <see cref="InitializeAsync"/>, and can be refreshed using <see cref="RefreshAvailableCameras(CancellationToken)"/>
 	/// </remarks>
 	IReadOnlyList<CameraInfo>? AvailableCameras { get; }
+	
+	/// <summary>
+	/// Gets a value indicating whether the camera provider has been successfully initialized.
+	/// </summary>
+	bool IsInitialized { get; }
 
 	/// <summary>
 	/// Refreshes <see cref="AvailableCameras"/> with the cameras available on device.
 	/// </summary>
 	/// <param name="token"></param>
 	/// <returns></returns>
 	[MemberNotNull(nameof(AvailableCameras))]
-	ValueTask RefreshAvailableCameras(CancellationToken token);
-
-	/// <summary>
-	/// Gets a value indicating whether the camera provider has been successfully initialized.
-	/// </summary>
-	bool IsInitialized { get; }
+	Task RefreshAvailableCameras(CancellationToken token);
 
 	/// <summary>
 	/// Initialize the camera provider by refreshing the <see cref="AvailableCameras"/>. 

src/CommunityToolkit.Maui.Camera/Providers/CameraProvider.android.cs

@@ -16,7 +16,7 @@ partial class CameraProvider
 {
 	readonly Context context = Android.App.Application.Context;
 
-	internal async partial ValueTask PlatformRefreshAvailableCameras(CancellationToken token)
+	private async partial ValueTask PlatformRefreshAvailableCameras(CancellationToken token)
 	{
 		var cameraProviderFuture = ProcessCameraProvider.GetInstance(context);
 

src/CommunityToolkit.Maui.Camera/Providers/CameraProvider.macios.cs

@@ -9,7 +9,7 @@ partial class CameraProvider
 {
 	static readonly AVCaptureDeviceType[] captureDevices = InitializeCaptureDevices();
 
-	internal partial ValueTask PlatformRefreshAvailableCameras(CancellationToken token)
+	private partial ValueTask PlatformRefreshAvailableCameras(CancellationToken token)
 	{
 		var discoverySession = AVCaptureDeviceDiscoverySession.Create(captureDevices, AVMediaTypes.Video, AVCaptureDevicePosition.Unspecified);
 		var availableCameras = new List<CameraInfo>();

src/CommunityToolkit.Maui.Camera/Providers/CameraProvider.net.cs

@@ -2,5 +2,5 @@ namespace CommunityToolkit.Maui.Core;
 
 partial class CameraProvider
 {
-	internal partial ValueTask PlatformRefreshAvailableCameras(CancellationToken token) => throw new NotSupportedException();
+	private partial ValueTask PlatformRefreshAvailableCameras(CancellationToken token) => throw new NotSupportedException();
 }

src/CommunityToolkit.Maui.Camera/Providers/CameraProvider.shared.cs

@@ -3,50 +3,67 @@
 /// <summary>
 /// Implementation that provides the ability to discover cameras that are attached to the current device.
 /// </summary>
-partial class CameraProvider : ICameraProvider
+partial class CameraProvider : ICameraProvider, IDisposable
 {
-	readonly Lock refreshLock = new();
-	Task? refreshTask;
+	readonly SemaphoreSlim refreshAvailableCamerasSemaphore = new(1, 1);
+	Task? refreshAvailableCamerasTask;
 
-	internal partial ValueTask PlatformRefreshAvailableCameras(CancellationToken token);
+	~CameraProvider()
+	{
+		Dispose(false);
+	}
 
 	/// <inheritdoc/>
-	public IReadOnlyList<CameraInfo>? AvailableCameras { get; private set; }
+	public bool IsInitialized => refreshAvailableCamerasTask?.IsCompletedSuccessfully is true;
 
 	/// <inheritdoc/>
-	public bool IsInitialized => refreshTask?.IsCompletedSuccessfully is true;
+	public IReadOnlyList<CameraInfo>? AvailableCameras { get; private set; }
 
-	ValueTask GetRefreshTask(CancellationToken token)
+	public void Dispose()
+	{
+		Dispose(true);
+		GC.SuppressFinalize(this);
+	}
+
+	/// <inheritdoc/>	
+	public async ValueTask InitializeAsync(CancellationToken token)
 	{
-		if (refreshTask is null || refreshTask.IsCompleted)
+		if (!IsInitialized)
 		{
-			refreshTask = PlatformRefreshAvailableCameras(token).AsTask();
+			await RefreshAvailableCameras(token);
 		}
-
-		return new ValueTask(refreshTask);
 	}
 
-	/// <inheritdoc/>	
-	public ValueTask InitializeAsync(CancellationToken token)
+	/// <inheritdoc/>
+	public async Task RefreshAvailableCameras(CancellationToken token)
 	{
-		lock (refreshLock)
+		await refreshAvailableCamerasSemaphore.WaitAsync(token);
+		
+		try
 		{
-			if (IsInitialized)
+			if (refreshAvailableCamerasTask is null || refreshAvailableCamerasTask.IsCompleted)
 			{
-				return ValueTask.CompletedTask;
+				refreshAvailableCamerasTask = PlatformRefreshAvailableCameras(token).AsTask();
 			}
 
-			return GetRefreshTask(token);
+			await refreshAvailableCamerasTask;
+		}
+		finally
+		{
+			refreshAvailableCamerasSemaphore.Release();
 		}
 	}
 
-	/// <inheritdoc/>
-	public ValueTask RefreshAvailableCameras(CancellationToken token)
+	void Dispose(bool disposing)
 	{
-		lock (refreshLock)
+		if (disposing)
 		{
-			return GetRefreshTask(token);
+			refreshAvailableCamerasSemaphore.Dispose();
+
+			refreshAvailableCamerasTask?.Dispose();
+			refreshAvailableCamerasTask = null;
 		}
 	}
-
-}
+	
+	private partial ValueTask PlatformRefreshAvailableCameras(CancellationToken token);
+}

src/CommunityToolkit.Maui.UnitTests/Mocks/MockCameraProvider.cs

@@ -8,17 +8,16 @@ public class MockCameraProvider : ICameraProvider
 
 	public bool IsInitialized { get; private set; }
 
-	public ValueTask InitializeAsync(CancellationToken token)
+	public async ValueTask InitializeAsync(CancellationToken token)
 	{
-		if (IsInitialized)
+		if (!IsInitialized)
 		{
-			return ValueTask.CompletedTask;
+			await RefreshAvailableCameras(token);
+			IsInitialized = true;
 		}
-		IsInitialized = true;
-		return RefreshAvailableCameras(token);
 	}
 
-	public ValueTask RefreshAvailableCameras(CancellationToken token)
+	public Task RefreshAvailableCameras(CancellationToken token)
 	{
 		AvailableCameras =
 		[
@@ -33,6 +32,6 @@ public ValueTask RefreshAvailableCameras(CancellationToken token)
 				])
 		];
 
-		return ValueTask.CompletedTask;
+		return Task.CompletedTask;
 	}
 }