Fix exception when using ALContext after disposing an extension (#2596)

* Start of fixing multiple calls to Dispose()

* Fix multiple disposal of UnmanagedLibrary

* Fix disposing of extension breaking parent context

* Create ExtensionsDisposalTests.cs

Author: midare160

src/Core/Silk.NET.Core/Loader/UnmanagedLibrary.cs

@@ -15,6 +15,8 @@ public class UnmanagedLibrary : IDisposable
         private static readonly LibraryLoader SPlatformDefaultLoader = LibraryLoader.GetPlatformDefaultLoader();
         private readonly LibraryLoader _loader;
 
+        private nint _handle;
+
         /// <summary>
         ///     Constructs a new NativeLibrary using the platform's default library loader.
         /// </summary>
@@ -55,7 +57,7 @@ public UnmanagedLibrary(string[] names, LibraryLoader loader) : this(names, load
         private UnmanagedLibrary(LibraryLoader loader, nint handle)
         {
             _loader = loader;
-            Handle = handle;
+            _handle = handle;
         }
 
         /// <summary>
@@ -82,7 +84,7 @@ public static bool TryCreate(string name, LibraryLoader loader, PathResolver pat
         public UnmanagedLibrary(string name, LibraryLoader loader, PathResolver pathResolver)
         {
             _loader = loader;
-            Handle = _loader.LoadNativeLibrary(name, pathResolver);
+            _handle = _loader.LoadNativeLibrary(name, pathResolver);
         }
 
         /// <summary>
@@ -94,20 +96,26 @@ public UnmanagedLibrary(string name, LibraryLoader loader, PathResolver pathReso
         public UnmanagedLibrary(string[] names, LibraryLoader loader, PathResolver pathResolver)
         {
             _loader = loader;
-            Handle = _loader.LoadNativeLibrary(names, pathResolver);
+            _handle = _loader.LoadNativeLibrary(names, pathResolver);
         }
 
         /// <summary>
         ///     The operating system handle of the loaded library.
         /// </summary>
-        public nint Handle { get; }
+        public nint Handle => _handle;
 
         /// <summary>
         ///     Frees the native library. Function pointers retrieved from this library will be void.
         /// </summary>
         public void Dispose()
         {
+            if (_handle == 0)
+            {
+                return;
+            }
+            
             _loader.FreeNativeLibrary(Handle);
+            _handle = 0;
         }
 
         /// <summary>

src/Core/Silk.NET.Core/Native/NativeAPI.cs

@@ -20,6 +20,13 @@ public NativeAPI(INativeContext ctx)
             Context = ctx;
         }
 
+        public override void Dispose()
+        {
+            Context.Dispose();
+            
+            base.Dispose();
+        }
+
         /// <summary>
         /// Whether or not an extension is present. This function might not be valid for some APIs.
         /// </summary>

src/Core/Silk.NET.Core/Native/NativeApiContainer.cs

@@ -31,9 +31,8 @@ public NativeApiContainer(INativeContext ctx)
 
         public IVTable CurrentVTable => _vTable;
 
-        public void Dispose()
+        public virtual void Dispose()
         {
-            _ctx.Dispose();
             CurrentVTable.Dispose();
         }
 

src/OpenAL/Silk.NET.OpenAL.Tests/ExtensionsDisposalTests.cs

@@ -0,0 +1,43 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using Silk.NET.OpenAL.Extensions.Enumeration;
+using Xunit;
+
+namespace Silk.NET.OpenAL.Tests;
+
+public class ExtensionsDisposalTests
+{
+    private static nint GetProcAddress(ALContext alc) =>
+        alc.Context.GetProcAddress("alcIsExtensionPresent");
+    
+    [Fact]
+    public unsafe void TestALContextExtensionDispose()
+    {
+        var alc = ALContext.GetApi();
+        alc.TryGetExtension<Enumeration>(null, out var ext);
+
+        // Disposing the same object multiple times should not throw
+        ext.Dispose();
+        alc.Dispose();
+
+        alc.Dispose();
+        ext.Dispose();
+    }
+
+    [Fact]
+    public unsafe void TestALContextExtensionDisposeState()
+    {
+        using var alc = ALContext.GetApi();
+        alc.TryGetExtension<Enumeration>(null, out var ext);
+        
+        var address = GetProcAddress(alc);
+        Assert.NotEqual(0, address);
+        
+        ext.Dispose();
+        
+        // Disposing the extension should not affect the parent context
+        address = GetProcAddress(alc);
+        Assert.NotEqual(0, address);
+    }
+}