Fixed loading multiple songs issue.

Harmonia.Core/Engine/BassAudioEngine.cs

@@ -6,6 +6,7 @@ namespace Harmonia.Core.Engine;
 public class BassAudioEngine : IAudioEngine, IDisposable
 {
     private readonly BaseMediaPlayer _mediaPlayer;
+    private readonly SemaphoreSlim _loadLock = new(1, 1);
 
     private CancellationTokenSource? _cancellationTokenSource;
 
@@ -136,27 +137,48 @@ public class BassAudioEngine : IAudioEngine, IDisposable
     private async Task<bool> LoadWaveSourceAsync(string fileName)
     {
         _cancellationTokenSource?.Cancel();
-        _cancellationTokenSource = new CancellationTokenSource();
 
-        CancellationToken token = _cancellationTokenSource.Token;
+        CancellationTokenSource cancellationTokenSource = new();
+        _cancellationTokenSource = cancellationTokenSource;
+
+        CancellationToken token = cancellationTokenSource.Token;
+
+        // Serialize loads so overlapping MediaPlayer.LoadAsync calls can't
+        // race and leave orphaned streams playing.
+        await _loadLock.WaitAsync(CancellationToken.None);
 
         try
-        {
-            await _mediaPlayer.LoadAsync(fileName);
-        }
-        catch (Exception ex)
         {
             if (token.IsCancellationRequested)
                 return false;
 
-            //return new Result(State.Exception, ex.Message);
-            throw new Exception("An error occurred - " + fileName, ex);
+            try
+            {
+                await _mediaPlayer.LoadAsync(fileName);
+            }
+            catch (Exception ex)
+            {
+                if (token.IsCancellationRequested)
+                    return false;
+
+                //return new Result(State.Exception, ex.Message);
+                throw new Exception("An error occurred - " + fileName, ex);
+            }
+
+            if (token.IsCancellationRequested)
+            {
+                // A newer load superseded this one; make sure this stream
+                // doesn't keep playing in the background.
+                _mediaPlayer.Stop();
+                return false;
+            }
+
+            return true;
+        }
+        finally
+        {
+            _loadLock.Release();
         }
-
-        if (token.IsCancellationRequested)
-            return false;
-
-        return true;
     }
 
     private void UpdateSource(string fileName)