From e10a03db1f82f3d084a47b9305d288a3cc13db02 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Daniel=20Qui=C3=B1ones?= <danielqp1@gmail.com>
Date: Wed, 6 Sep 2023 02:41:50 +0200
Subject: [PATCH] Fixed exception when unexpected disposed RtMidiCallback

Keep reference to midi event callback in RtMidiIn interop to prevent GC bumbling off with the handler
---
 RtMidi.Net/InteropServices/RtMidiIn.cs |  8 ++++++++
 WorkerTest/Program.cs                  |  2 +-
 WorkerTest/Worker.cs                   | 20 +++++++++++++-------
 3 files changed, 22 insertions(+), 8 deletions(-)

diff --git a/RtMidi.Net/InteropServices/RtMidiIn.cs b/RtMidi.Net/InteropServices/RtMidiIn.cs
index c372988..da30a16 100644
--- 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);
     }
 }
\ No newline at end of file
diff --git a/WorkerTest/Program.cs b/WorkerTest/Program.cs
index 9c5353c..36183a3 100644
--- 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
index cc9da5c..d9c2319 100644
--- 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);
+                }
             }
         }