Fixed exception when unexpected disposed RtMidiCallback

Keep reference to midi event callback in RtMidiIn interop to prevent GC bumbling off with the handler
Daniel127 · Sep 6, 2023 · e10a03d · e10a03d
1 parent afc4adc
commit e10a03d
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Showing 3 changed files with 22 additions and 8 deletions.
diff --git a/RtMidi.Net/InteropServices/RtMidiIn.cs b/RtMidi.Net/InteropServices/RtMidiIn.cs
@@ -16,6 +16,12 @@ namespace RtMidi.Net.InteropServices;
 /// </summary>
 internal class RtMidiIn : RtMidiBase
 {
+#pragma warning disable IDE0052
+    // ReSharper disable once NotAccessedField.Local
+    // Used to prevent garbage collection of the delegate
+    private RtMidiCallback? _midiCallback;
+#pragma warning restore IDE0052
+
     /// <summary>
     /// Default constructor
     /// </summary>
@@ -67,6 +73,7 @@ public override MidiApi GetCurrentApi()
     /// passed to the callback function whenever it is called.</param>
     public void SetCallback(RtMidiCallback callback, byte[]? userData)
     {
+        _midiCallback = callback;
         RtMidiInterop.rtmidi_in_set_callback(RtMidiPtr, callback, userData);
     }
 
@@ -126,6 +133,7 @@ public void IgnoreTypes(bool midiSysex = true, bool midiTime = true, bool midiSe
     /// <inheritdoc />
     protected override void ReleaseUnmanagedResources()
     {
+        _midiCallback = null;
         RtMidiInterop.rtmidi_in_free(RtMidiPtr);
     }
 }
diff --git a/WorkerTest/Program.cs b/WorkerTest/Program.cs
@@ -1,6 +1,6 @@
 using WorkerTest;
 
-IHost host = Host.CreateDefaultBuilder(args)
+var host = Host.CreateDefaultBuilder(args)
     .ConfigureServices(services =>
     {
         services.AddHostedService<Worker>();

diff --git a/WorkerTest/Worker.cs b/WorkerTest/Worker.cs
@@ -9,6 +9,7 @@ public class Worker : BackgroundService
     {
         private readonly ILogger<Worker> _logger;
         private MidiInputClient? _midiInputClient;
+        private const bool UseEventHandler = true; //Change to test
 
         /// <summary>
         /// Constructor
@@ -29,12 +30,14 @@ public override async Task StartAsync(CancellationToken cancellationToken)
             }
             if (devices.Any())
             {
-                var devicePort = 1u; //TODO Change device to test
+                var devicePort = 1u; //Change device to test
                 var device = MidiManager.GetDeviceInfo(devicePort, MidiDeviceType.Input);
                 _midiInputClient = new MidiInputClient(device);
-                //TODO The event throws an exception after a while, i'm not sure why
-                //_midiInputClient.OnMessageReceived += MidiClient_OnMessageReceived;
-                //_midiInputClient.ActivateMessageReceivedEvent();
+                if (UseEventHandler)
+                {
+                    _midiInputClient.OnMessageReceived += MidiClient_OnMessageReceived;
+                    _midiInputClient.ActivateMessageReceivedEvent();
+                }
                 _midiInputClient.Open();
             }
             else
@@ -50,10 +53,13 @@ public override async Task StartAsync(CancellationToken cancellationToken)
         protected override async Task ExecuteAsync(CancellationToken stoppingToken)
         {
             _logger.LogInformation("Executing");
-            while (!stoppingToken.IsCancellationRequested)
+            if (!UseEventHandler)
             {
-                var (message, _) = await _midiInputClient!.GetMessageAsync(stoppingToken);
-                OnMessageReceived(message);
+                while (!stoppingToken.IsCancellationRequested)
+                {
+                    var (message, _) = await _midiInputClient!.GetMessageAsync(stoppingToken);
+                    OnMessageReceived(message);
+                }
             }
         }