resource stuff

Nerfed.Runtime/Resource/ResourceManager.cs

@@ -1,43 +1,209 @@
+using System;
+using System.Collections.Concurrent;
+using System.Collections.Generic;
+using System.IO;
+using System.Threading;
+
 namespace Nerfed.Runtime;
 
+/// <summary>
+/// A highly scalable, multithreaded resource manager that handles asynchronous asset 
+/// loading and automatic reference-counted memory management.
+/// </summary>
 public static class ResourceManager
 {
-    private const string rootName = "Resources";
-    private static readonly Dictionary<string, Resource> loadedResources = new Dictionary<string, Resource>();
+    private const string RootName = "Resources";
 
-    public static T Load<T>(string resourcePath) where T : Resource
+    // Track resources by their Guid ID instead of simple strings.
+    private static readonly ConcurrentDictionary<Guid, Resource> _resourceCache = new();
+
+    // Mapping a string path to its runtime Guid identifier
+    private static readonly ConcurrentDictionary<string, Guid> _pathToGuid = new();
+
+    // Queues for background processing
+    private static readonly ConcurrentQueue<Resource> _loadQueue = new();
+
+    // Loader threads
+    private static readonly Thread _loaderThread;
+    private static bool _isRunning = true;
+
+    // A registry of how to create concrete Resource instances from a generic type without massive switch statements.
+    private static readonly Dictionary<Type, Func<Resource>> _resourceFactories = new()
     {
-        if (loadedResources.TryGetValue(resourcePath, out Resource resource))
+        { typeof(Shader), () => new Shader() }
+    };
+
+    static ResourceManager()
+    {
+        _loaderThread = new Thread(LoaderWorkerLoop)
         {
-            return (T)resource;
+            Name = "Nerfed Asset Loader",
+            IsBackground = true,
+            Priority = ThreadPriority.BelowNormal // Keeps CPU time focused on the main game loop
+        };
+        _loaderThread.Start();
+    }
+
+    /// <summary>
+    /// Synchronously shuts down the loader thread when the engine closes.
+    /// </summary>
+    public static void Shutdown()
+    {
+        _isRunning = false;
+        _loaderThread.Join();
+    }
+
+    /// <summary>
+    /// Registers a new resource type factory so the manager knows how to instantiate it.
+    /// Example: RegisterResourceType<Texture>(() => new Texture());
+    /// </summary>
+    public static void RegisterResourceType<T>(Func<T> factory) where T : Resource
+    {
+        _resourceFactories[typeof(T)] = factory;
+    }
+
+    /// <summary>
+    /// Gets the Guid associated with a specific asset path, making an initial id pass if required.
+    /// In a fully baked engine, the Guid is known at compile time or baked in the map data.
+    /// </summary>
+    public static Guid GetId(string resourcePath)
+    {
+        return _pathToGuid.GetOrAdd(resourcePath, _ => Guid.NewGuid());
+    }
+
+    /// <summary>
+    /// Begins an asynchronous load for a resource by its Guid.
+    /// In ECS systems, Entities should strictly prefer this overload over the string one.
+    /// </summary>
+    public static T Retain<T>(Guid id, string expectedPath) where T : Resource
+    {
+        var resource = _resourceCache.GetOrAdd(id, (assetId) =>
+        {
+            if (!_resourceFactories.TryGetValue(typeof(T), out var factory))
+            {
+                throw new Exception($"Failed to create resource. No factory registered for {typeof(T).Name}");
+            }
+
+            var newResource = factory();
+            newResource.Id = assetId;
+            // The path is still required so the background thread knows which file to open from disk.
+            newResource.Path = expectedPath; 
+            newResource.State = ResourceState.Unloaded;
+            
+            return newResource;
+        });
+
+        lock (resource)
+        {
+            resource.ReferenceCount++;
+            
+            if (resource.State == ResourceState.Unloaded)
+            {
+                resource.State = ResourceState.Queued;
+                _loadQueue.Enqueue(resource);
+            }
         }
 
-        if (typeof(T) == typeof(Shader))
-        {
-            resource = new Shader();
-        }
-        else
-        {
-            throw new Exception("Failed to create resource");
-        }
-
-        Assert.Always(resource != null);
-        resource.Path = resourcePath;
-        resource.Load(StorageContainer.OpenStream(Path.Combine(AppContext.BaseDirectory, rootName, resourcePath) + ".bin"));
-
-        loadedResources.Add(resourcePath, resource);
         return (T)resource;
     }
 
-    public static void Unload(Resource resource)
+    /// <summary>
+    /// Begins an asynchronous load utilizing the string path to find the matching Guid. 
+    /// This should generally be avoided in tight ECS loops.
+    /// </summary>
+    public static T Retain<T>(string resourcePath) where T : Resource
     {
-        if (!loadedResources.ContainsKey(resource.Path))
-        {
-            return;
-        }
+        Guid id = GetId(resourcePath);
+        return Retain<T>(id, resourcePath);
+    }
 
-        resource.Unload();
-        resource.Path = string.Empty;
-        loadedResources.Remove(resource.Path);
+    /// <summary>
+    /// Gets the current loading state of a resource by its Guid without altering its reference count.
+    /// </summary>
+    public static ResourceState GetState(Guid id)
+    {
+        if (_resourceCache.TryGetValue(id, out var resource))
+        {
+            return resource.State;
+        }
+        return ResourceState.Unloaded;
+    }
+
+    /// <summary>
+    /// Decrements the reference count of a resource by its Guid.
+    /// </summary>
+    public static void Release(Guid id)
+    {
+        if (_resourceCache.TryGetValue(id, out var resource))
+        {
+            Release(resource);
+        }
+    }
+
+    /// <summary>
+    /// Decrements the reference count of a resource. 
+    /// If the count reaches 0, the asset is automatically unloaded from memory.
+    /// </summary>
+    public static void Release(Resource resource)
+    {
+        if (resource == null) return;
+
+        lock (resource)
+        {
+            resource.ReferenceCount--;
+
+            if (resource.ReferenceCount <= 0)
+            {
+                // Fully unused! We should unload it safely.
+                if (resource.State == ResourceState.Loaded)
+                {
+                    resource.Unload();
+                }
+
+                resource.State = ResourceState.Unloaded;
+                _resourceCache.TryRemove(resource.Id, out _);
+            }
+        }
+    }
+
+    /// <summary>
+    /// Background thread loop that pulls from the queue and does the slow file I/O operations.
+    /// </summary>
+    private static void LoaderWorkerLoop()
+    {
+        while (_isRunning)
+        {
+            if (_loadQueue.TryDequeue(out var resource))
+            {
+                // Safety check: Was the resource released before we even got around to loading it?
+                if (resource.ReferenceCount <= 0)
+                {
+                    resource.State = ResourceState.Unloaded;
+                    continue;
+                }
+
+                try
+                {
+                    resource.State = ResourceState.Loading;
+                    string fullPath = Path.Combine(AppContext.BaseDirectory, RootName, resource.Id.ToString()) + ".bin";
+                    
+                    // Do the slow synchronous disk read
+                    using var stream = StorageContainer.OpenStream(fullPath);
+                    resource.Load(stream);
+
+                    resource.State = ResourceState.Loaded;
+                }
+                catch (Exception e)
+                {
+                    Log.Error($"Failed to background load asset '{resource.Path}': {e.Message}");
+                    resource.State = ResourceState.Failed;
+                }
+            }
+            else
+            {
+                // Sleep cleanly if queue is empty to avoid burning total CPU usage on an infinite while-loop
+                Thread.Sleep(10);
+            }
+        }
     }
 }