Add SemaphoreSlim

Author: TheCodeTraveler

src/CommunityToolkit/Xamarin.CommunityToolkit/ObjectModel/Internals/BaseCommand.shared.cs

@@ -1,5 +1,7 @@
 using System;
 using System.ComponentModel;
+using System.Threading;
+using System.Threading.Tasks;
 using Xamarin.CommunityToolkit.Helpers;
 using Xamarin.Forms;
 
@@ -12,9 +14,10 @@ namespace Xamarin.CommunityToolkit.ObjectModel.Internals
 	public abstract partial class BaseCommand<TCanExecute>
 	{
 		readonly Func<TCanExecute?, bool> canExecute;
+		readonly SemaphoreSlim semaphoreSlim = new SemaphoreSlim(1, 1);
 		readonly DelegateWeakEventManager weakEventManager = new DelegateWeakEventManager();
 
-		volatile int executionCount;
+		int executionCount;
 
 		/// <summary>
 		/// Initializes BaseCommand
@@ -51,18 +54,11 @@ protected int ExecutionCount
 			get => executionCount;
 			set
 			{
-				var shouldRaiseCanExecuteChanged = (AllowsMultipleExecutions, executionCount, value) switch
-				{
-					(true, _, _) => false,
-					(false, 0, >0) => true,
-					(false, >0, 0) => true,
-					(false, _, _) => false
-				};
+				var previousExecutionCount = executionCount;
 
 				executionCount = value;
 
-				if (shouldRaiseCanExecuteChanged)
-					RaiseCanExecuteChanged();
+				HandleExecutionCountChanged(previousExecutionCount, value).SafeFireAndForget();
 			}
 		}
 
@@ -95,5 +91,28 @@ public void RaiseCanExecuteChanged()
 		/// </summary>
 		[EditorBrowsable(EditorBrowsableState.Never)]
 		public void ChangeCanExecute() => RaiseCanExecuteChanged();
+
+		async Task HandleExecutionCountChanged(int updatedExecutionCount, int previousExecutionCount)
+		{
+			await semaphoreSlim.WaitAsync().ConfigureAwait(true);
+
+			try
+			{
+				var shouldRaiseCanExecuteChanged = (AllowsMultipleExecutions, updatedExecutionCount, previousExecutionCount) switch
+				{
+					(true, _, _) => false,
+					(false, 0, > 0) => true,
+					(false, > 0, 0) => true,
+					(false, _, _) => false
+				};
+
+				if (shouldRaiseCanExecuteChanged)
+					RaiseCanExecuteChanged();
+			}
+			finally
+			{
+				semaphoreSlim.Release();
+			}
+		}
 	}
 }