1 files changed, 270 insertions, 0 deletions
diff --git a/modules/mono/glue/GodotSharp/GodotPlugins/Main.cs b/modules/mono/glue/GodotSharp/GodotPlugins/Main.cs
new file mode 100644
index 0000000000..8308bada24
--- /dev/null
+++ b/modules/mono/glue/GodotSharp/GodotPlugins/Main.cs
@@ -0,0 +1,270 @@
+using System;
+using System.Collections.Generic;
+using System.IO;
+using System.Reflection;
+using System.Runtime.CompilerServices;
+using System.Runtime.InteropServices;
+using System.Runtime.Loader;
+using Godot.Bridge;
+using Godot.NativeInterop;
+
+namespace GodotPlugins
+{
+    public static class Main
+    {
+        // IMPORTANT:
+        // Keeping strong references to the AssemblyLoadContext (our PluginLoadContext) prevents
+        // it from being unloaded. To avoid issues, we wrap the reference in this class, and mark
+        // all the methods that access it as non-inlineable. This way we prevent local references
+        // (either real or introduced by the JIT) to escape the scope of these methods due to
+        // inlining, which could keep the AssemblyLoadContext alive while trying to unload.
+        private sealed class PluginLoadContextWrapper
+        {
+            private PluginLoadContext? _pluginLoadContext;
+
+            public string? AssemblyLoadedPath
+            {
+                [MethodImpl(MethodImplOptions.NoInlining)]
+                get => _pluginLoadContext?.AssemblyLoadedPath;
+            }
+
+            [MethodImpl(MethodImplOptions.NoInlining)]
+            public static (Assembly, PluginLoadContextWrapper) CreateAndLoadFromAssemblyName(
+                AssemblyName assemblyName,
+                string pluginPath,
+                ICollection<string> sharedAssemblies,
+                AssemblyLoadContext mainLoadContext
+            )
+            {
+                var wrapper = new PluginLoadContextWrapper();
+                wrapper._pluginLoadContext = new PluginLoadContext(
+                    pluginPath, sharedAssemblies, mainLoadContext);
+                var assembly = wrapper._pluginLoadContext.LoadFromAssemblyName(assemblyName);
+                return (assembly, wrapper);
+            }
+
+            [MethodImpl(MethodImplOptions.NoInlining)]
+            public WeakReference CreateWeakReference()
+            {
+                return new WeakReference(_pluginLoadContext, trackResurrection: true);
+            }
+
+            [MethodImpl(MethodImplOptions.NoInlining)]
+            internal void Unload()
+            {
+                _pluginLoadContext?.Unload();
+                _pluginLoadContext = null;
+            }
+        }
+
+        private static readonly List<AssemblyName> SharedAssemblies = new();
+        private static readonly Assembly CoreApiAssembly = typeof(Godot.Object).Assembly;
+        private static Assembly? _editorApiAssembly;
+        private static PluginLoadContextWrapper? _projectLoadContext;
+
+        private static readonly AssemblyLoadContext MainLoadContext =
+            AssemblyLoadContext.GetLoadContext(Assembly.GetExecutingAssembly()) ??
+            AssemblyLoadContext.Default;
+
+        private static DllImportResolver? _dllImportResolver;
+
+        // Right now we do it this way for simplicity as hot-reload is disabled. It will need to be changed later.
+        [UnmanagedCallersOnly]
+        // ReSharper disable once UnusedMember.Local
+        private static unsafe godot_bool InitializeFromEngine(IntPtr godotDllHandle, godot_bool editorHint,
+            PluginsCallbacks* pluginsCallbacks, ManagedCallbacks* managedCallbacks,
+            IntPtr unmanagedCallbacks, int unmanagedCallbacksSize)
+        {
+            try
+            {
+                _dllImportResolver = new GodotDllImportResolver(godotDllHandle).OnResolveDllImport;
+
+                SharedAssemblies.Add(CoreApiAssembly.GetName());
+                NativeLibrary.SetDllImportResolver(CoreApiAssembly, _dllImportResolver);
+
+                AlcReloadCfg.Configure(alcReloadEnabled: editorHint.ToBool());
+                NativeFuncs.Initialize(unmanagedCallbacks, unmanagedCallbacksSize);
+
+                if (editorHint.ToBool())
+                {
+                    _editorApiAssembly = Assembly.Load("GodotSharpEditor");
+                    SharedAssemblies.Add(_editorApiAssembly.GetName());
+                    NativeLibrary.SetDllImportResolver(_editorApiAssembly, _dllImportResolver);
+                }
+
+                *pluginsCallbacks = new()
+                {
+                    LoadProjectAssemblyCallback = &LoadProjectAssembly,
+                    LoadToolsAssemblyCallback = &LoadToolsAssembly,
+                    UnloadProjectPluginCallback = &UnloadProjectPlugin,
+                };
+
+                *managedCallbacks = ManagedCallbacks.Create();
+
+                return godot_bool.True;
+            }
+            catch (Exception e)
+            {
+                Console.Error.WriteLine(e);
+                return godot_bool.False;
+            }
+        }
+
+        [StructLayout(LayoutKind.Sequential)]
+        private struct PluginsCallbacks
+        {
+            public unsafe delegate* unmanaged<char*, godot_string*, godot_bool> LoadProjectAssemblyCallback;
+            public unsafe delegate* unmanaged<char*, IntPtr, int, IntPtr> LoadToolsAssemblyCallback;
+            public unsafe delegate* unmanaged<godot_bool> UnloadProjectPluginCallback;
+        }
+
+        [UnmanagedCallersOnly]
+        private static unsafe godot_bool LoadProjectAssembly(char* nAssemblyPath, godot_string* outLoadedAssemblyPath)
+        {
+            try
+            {
+                if (_projectLoadContext != null)
+                    return godot_bool.True; // Already loaded
+
+                string assemblyPath = new(nAssemblyPath);
+
+                (var projectAssembly, _projectLoadContext) = LoadPlugin(assemblyPath);
+
+                string loadedAssemblyPath = _projectLoadContext.AssemblyLoadedPath ?? assemblyPath;
+                *outLoadedAssemblyPath = Marshaling.ConvertStringToNative(loadedAssemblyPath);
+
+                ScriptManagerBridge.LookupScriptsInAssembly(projectAssembly);
+
+                return godot_bool.True;
+            }
+            catch (Exception e)
+            {
+                Console.Error.WriteLine(e);
+                return godot_bool.False;
+            }
+        }
+
+        [UnmanagedCallersOnly]
+        private static unsafe IntPtr LoadToolsAssembly(char* nAssemblyPath,
+            IntPtr unmanagedCallbacks, int unmanagedCallbacksSize)
+        {
+            try
+            {
+                string assemblyPath = new(nAssemblyPath);
+
+                if (_editorApiAssembly == null)
+                    throw new InvalidOperationException("The Godot editor API assembly is not loaded.");
+
+                var (assembly, _) = LoadPlugin(assemblyPath);
+
+                NativeLibrary.SetDllImportResolver(assembly, _dllImportResolver!);
+
+                var method = assembly.GetType("GodotTools.GodotSharpEditor")?
+                    .GetMethod("InternalCreateInstance",
+                        BindingFlags.Static | BindingFlags.NonPublic | BindingFlags.Public);
+
+                if (method == null)
+                {
+                    throw new MissingMethodException("GodotTools.GodotSharpEditor",
+                        "InternalCreateInstance");
+                }
+
+                return (IntPtr?)method
+                           .Invoke(null, new object[] { unmanagedCallbacks, unmanagedCallbacksSize })
+                       ?? IntPtr.Zero;
+            }
+            catch (Exception e)
+            {
+                Console.Error.WriteLine(e);
+                return IntPtr.Zero;
+            }
+        }
+
+        private static (Assembly, PluginLoadContextWrapper) LoadPlugin(string assemblyPath)
+        {
+            string assemblyName = Path.GetFileNameWithoutExtension(assemblyPath);
+
+            var sharedAssemblies = new List<string>();
+
+            foreach (var sharedAssembly in SharedAssemblies)
+            {
+                string? sharedAssemblyName = sharedAssembly.Name;
+                if (sharedAssemblyName != null)
+                    sharedAssemblies.Add(sharedAssemblyName);
+            }
+
+            return PluginLoadContextWrapper.CreateAndLoadFromAssemblyName(
+                new AssemblyName(assemblyName), assemblyPath, sharedAssemblies, MainLoadContext);
+        }
+
+        [UnmanagedCallersOnly]
+        private static godot_bool UnloadProjectPlugin()
+        {
+            try
+            {
+                return UnloadPlugin(ref _projectLoadContext).ToGodotBool();
+            }
+            catch (Exception e)
+            {
+                Console.Error.WriteLine(e);
+                return godot_bool.False;
+            }
+        }
+
+        private static bool UnloadPlugin(ref PluginLoadContextWrapper? pluginLoadContext)
+        {
+            try
+            {
+                if (pluginLoadContext == null)
+                    return true;
+
+                Console.WriteLine("Unloading assembly load context...");
+
+                var alcWeakReference = pluginLoadContext.CreateWeakReference();
+
+                pluginLoadContext.Unload();
+                pluginLoadContext = null;
+
+                int startTimeMs = Environment.TickCount;
+                bool takingTooLong = false;
+
+                while (alcWeakReference.IsAlive)
+                {
+                    GC.Collect(GC.MaxGeneration, GCCollectionMode.Forced);
+                    GC.WaitForPendingFinalizers();
+
+                    if (!alcWeakReference.IsAlive)
+                        break;
+
+                    int elapsedTimeMs = Environment.TickCount - startTimeMs;
+
+                    if (!takingTooLong && elapsedTimeMs >= 2000)
+                    {
+                        takingTooLong = true;
+
+                        // TODO: How to log from GodotPlugins? (delegate pointer?)
+                        Console.Error.WriteLine("Assembly unloading is taking longer than expected...");
+                    }
+                    else if (elapsedTimeMs >= 5000)
+                    {
+                        // TODO: How to log from GodotPlugins? (delegate pointer?)
+                        Console.Error.WriteLine(
+                            "Failed to unload assemblies. Possible causes: Strong GC handles, running threads, etc.");
+
+                        return false;
+                    }
+                }
+
+                Console.WriteLine("Assembly load context unloaded successfully.");
+
+                return true;
+            }
+            catch (Exception e)
+            {
+                // TODO: How to log exceptions from GodotPlugins? (delegate pointer?)
+                Console.Error.WriteLine(e);
+                return false;
+            }
+        }
+    }
+}