use semaphore instead of lock

Author: Edward Miller

src/Controls/src/Core/ImageSource.cs

@@ -11,7 +11,7 @@ namespace Microsoft.Maui.Controls
 	[System.ComponentModel.TypeConverter(typeof(ImageSourceConverter))]
 	public abstract partial class ImageSource : Element
 	{
-		readonly object _synchandle = new object();
+		readonly SemaphoreSlim _cancellationTokenSourceLock = new(1, 1);
 		CancellationTokenSource _cancellationTokenSource;
 
 		TaskCompletionSource<bool> _completionSource;
@@ -121,7 +121,7 @@ public static implicit operator ImageSource(Uri uri)
 			return FromUri(uri);
 		}
 
-		private protected void OnLoadingCompleted(bool cancelled)
+		private protected async Task OnLoadingCompleted(bool cancelled)
 		{
 			if (!IsLoading || _completionSource == null)
 				return;
@@ -130,18 +130,28 @@ private protected void OnLoadingCompleted(bool cancelled)
 			if (tcs != null)
 				tcs.SetResult(cancelled);
 
-			lock (_synchandle)
+			await _cancellationTokenSourceLock.WaitAsync();
+			try
 			{
 				CancellationTokenSource = null;
 			}
+			finally
+			{
+				_cancellationTokenSourceLock.Release();
+			}
 		}
 
-		private protected void OnLoadingStarted()
+		private protected async Task OnLoadingStarted()
 		{
-			lock (_synchandle)
+			await _cancellationTokenSourceLock.WaitAsync();
+			try
 			{
 				CancellationTokenSource = new CancellationTokenSource();
 			}
+			finally
+			{
+				_cancellationTokenSourceLock.Release();
+			}
 		}
 
 		protected void OnSourceChanged()

src/Controls/src/Core/StreamImageSource.cs

@@ -35,17 +35,17 @@ async Task<Stream> IStreamImageSource.GetStreamAsync(CancellationToken userToken
 			if (IsEmpty)
 				return null;
 
-			OnLoadingStarted();
+			await OnLoadingStarted();
 			userToken.Register(CancellationTokenSource.Cancel);
 			Stream stream = null;
 			try
 			{
 				stream = await Stream(CancellationTokenSource.Token);
-				OnLoadingCompleted(false);
+				await OnLoadingCompleted(false);
 			}
 			catch (OperationCanceledException)
 			{
-				OnLoadingCompleted(true);
+				await OnLoadingCompleted(true);
 				throw;
 			}
 			return stream;

src/Controls/src/Core/UriImageSource.cs

@@ -56,18 +56,18 @@ async Task<Stream> IStreamImageSource.GetStreamAsync(CancellationToken userToken
 			if (IsEmpty)
 				return null;
 
-			OnLoadingStarted();
+			await OnLoadingStarted();
 			userToken.Register(CancellationTokenSource.Cancel);
 			Stream stream;
 
 			try
 			{
 				stream = await GetStreamAsync(Uri, CancellationTokenSource.Token);
-				OnLoadingCompleted(false);
+				await OnLoadingCompleted(false);
 			}
 			catch (OperationCanceledException)
 			{
-				OnLoadingCompleted(true);
+				await OnLoadingCompleted(true);
 				throw;
 			}
 			catch (Exception ex)