Async asset loading

2025-08-30 23:52:54 +05:00
parent 9fdd997be6
commit 3f1c0aa2f8
6 changed files with 309 additions and 78 deletions
--- a/src/assets.zig
+++ b/src/assets.zig
@@ -1,104 +1,285 @@
 const std = @import("std");
-const sdl = @import("sdl");
 const err = @import("error.zig");
-const c = @import("c.zig");
-const comp = @import("components.zig");
 const Game = @import("game.zig");
-const Graphics = @import("graphics.zig");
+const FileLoader = @import("assets/file.zig");
+const TextureLoader = @import("assets/texture.zig");
 const Assets = @This();

-const Storage = comp.Storage(Asset, .{});
+pub const Texture = AssetContainer(TextureLoader);

-var storage: Storage = undefined;
+const WORKERS_MAX = 4;
+var next_worker_update: usize = 0;
+var workers: [WORKERS_MAX]WorkerState = undefined;
+const WorkerState = struct {
+    running: bool = false,
+    thread: ?std.Thread = null,
+};
+
+const AssetMap = std.HashMapUnmanaged(AssetId, *AssetCell, AssetContext, 80);
+var asset_map_mutex: std.Thread.Mutex = .{};
+var asset_map: AssetMap = undefined;
+
+const RequestBoard = std.ArrayListUnmanaged(*AssetCell);
+var request_board_mutex: std.Thread.Mutex = .{};
+var request_board: RequestBoard = undefined;
+var request_board_counter: usize = 0;
+
+const FreeBoard = std.ArrayListUnmanaged(*AssetCell);
+var free_board_mutex: std.Thread.Mutex = .{};
+var free_board: FreeBoard = undefined;
+
+const AssetId = struct {
+    type: AssetType,
+    path: []const u8,
+};
+const AssetContext = struct {
+    pub fn hash(self: @This(), key: AssetId) u64 {
+        _ = self;
+        var hasher = std.hash.Wyhash.init(@intFromEnum(key.type));
+        hasher.update(key.path);
+        return hasher.final();
+    }
+    pub fn eql(self: @This(), a: AssetId, b: AssetId) bool {
+        _ = self;
+        return a.type == b.type and std.mem.eql(u8, a.path, b.path);
+    }
+};
+
+pub const LoadError = error{
+    DependencyError,
+} || std.mem.Allocator.Error || std.fs.File.OpenError || std.fs.File.ReadError;

 pub const AssetType = enum {
+    file,
    texture,
-};
-pub const Texture = struct {
-    handle: Storage.Key,
+
+    pub fn getType(comptime self: @This()) type {
+        return switch (self) {
+            .file => FileLoader,
+            .texture => TextureLoader,
+        };
+    }
 };

-const Asset = struct {
+const AssetState = union(enum) {
+    not_loaded,
+    loaded,
+    fail: LoadError,
+};
+
+pub const AssetCell = struct {
+    mutex: std.Thread.Mutex,
+    type: AssetType,
+    data: *void,
    path: []const u8,
-    data: union(AssetType) {
-        texture: AssetTexture,
+    loader: *const fn (*AssetCell, std.mem.Allocator) LoadError!void,
+    unloader: *const fn (*AssetCell, std.mem.Allocator) void,
+    state: AssetState,
+    counter: usize,
+
+    fn load(self: *AssetCell, alloc: std.mem.Allocator) void {
+        self.loader(self, alloc) catch |e| {
+            self.state = .{ .fail = e };
+            return;
+        };
+        self.state = .loaded;
+    }
+    fn unload(self: *AssetCell, alloc: std.mem.Allocator) void {
+        self.unloader(self, alloc);
+    }
+};
+
+pub fn AssetContainer(comptime T: type) type {
+    return struct {
+        data_pointer: ?*T = null,
+        asset_pointer: *AssetCell,
+        last_state: AssetState = .not_loaded,
+
+        pub fn get(self: *@This()) ?*T {
+            switch (self.last_state) {
+                .loaded => {
+                    @branchHint(.likely);
+                    return self.data_pointer;
                },
-};
-pub const AssetTexture = struct {
-    texture: *sdl.GPUTexture,
-    sampler: *sdl.GPUSampler,
-};
+                .fail => {
+                    return null;
+                },
+                .not_loaded => {
+                    if (self.asset_pointer.mutex.tryLock()) {
+                        defer self.asset_pointer.mutex.unlock();
+                        self.last_state = self.asset_pointer.state;
+                    }
+                    if (self.last_state == .loaded) {
+                        self.data_pointer = @alignCast(@ptrCast(self.asset_pointer.data));
+                        return self.data_pointer;
+                    } else return null;
+                },
+            }
+        }
+        /// To be used by worker threads to request other assets
+        pub fn getSync(self: *@This()) !*T {
+            sw: switch (self.last_state) {
+                .loaded => {
+                    return self.data_pointer.?;
+                },
+                .fail => |e| {
+                    return e;
+                },
+                .not_loaded => {
+                    // TODO: Do something else while the asset is locked?
+                    self.asset_pointer.mutex.lock();
+                    defer self.asset_pointer.mutex.unlock();
+                    self.asset_pointer.load(Game.alloc);
+                    self.last_state = self.asset_pointer.state;
+                    if (self.last_state == .loaded) {
+                        self.data_pointer = @alignCast(@ptrCast(self.asset_pointer.data));
+                    }
+                    continue :sw self.last_state;
+                },
+            }
+        }
+    };
+}

 pub fn init() void {
-    Assets.storage = Storage.init();
+    Assets.next_worker_update = 0;
+    Assets.workers = .{WorkerState{}} ** WORKERS_MAX;
+    Assets.asset_map_mutex = .{};
+    Assets.asset_map = AssetMap.empty;
+    Assets.request_board_mutex = .{};
+    Assets.request_board = RequestBoard.empty;
+    Assets.request_board_counter = 0;
+    Assets.free_board_mutex = .{};
+    Assets.free_board = FreeBoard.empty;
 }
 pub fn deinit() void {
-    var iter = Assets.storage.iter();
+    for (&Assets.workers) |*worker| {
+        if (worker.thread == null) continue;
+        worker.thread.?.join();
+    }
+    var iter = Assets.asset_map.valueIterator();
    while (iter.next()) |asset| {
-        Assets.freeAsset(asset);
+        std.debug.assert(asset.*.counter == 0);
+        if (asset.*.state == .loaded)
+            asset.*.unload(Game.alloc);
+        Game.alloc.destroy(asset.*);
    }
-    Assets.storage.deinit();
+    Assets.asset_map.clearAndFree(Game.alloc);
+    Assets.request_board.clearAndFree(Game.alloc);
+    Assets.free_board.clearAndFree(Game.alloc);
 }
-pub fn load(comptime asset_type: AssetType, path: []const u8) typeFromAssetType(asset_type) {
-    switch (asset_type) {
-        .texture => {
-            const data = loadFile(Game.alloc, path) catch |e| err.file(e, path);
-            var x: i32 = undefined;
-            var y: i32 = undefined;
-            var z: i32 = undefined;
-            const image = c.stbi_load_from_memory(@ptrCast(data), @intCast(data.len), &x, &y, &z, 4);
-            Game.alloc.free(data);
-            if (image == null) err.stbi();
-            const image_slice = image[0..@intCast(x * y * z)];
-            const texture, const sampler = Graphics.loadTexture(@intCast(x), @intCast(y), image_slice);
-            c.stbi_image_free(image);
-            return .{ .handle = Assets.storage.add(.{
-                .path = path,
-                .data = .{ .texture = .{
-                    .texture = texture,
-                    .sampler = sampler,
-                } },
-            }) };
-        },
+pub fn update() void {
+    const worker = &Assets.workers[Assets.next_worker_update];
+    if (!@atomicLoad(bool, &worker.running, .acquire) and worker.thread != null) {
+        worker.thread.?.join();
+        worker.thread = null;
    }
-}
-pub fn free(asset: anytype) void {
-    if (Assets.storage.free(asset.handle)) |stored| {
-        freeAsset(stored);
+    if (worker.thread == null and @atomicLoad(usize, &Assets.request_board_counter, .monotonic) > 4 * Assets.next_worker_update) {
+        worker.running = true;
+        worker.thread = std.Thread.spawn(.{}, loaderLoop, .{Assets.next_worker_update}) catch err.oom();
    }
-}
-pub fn freeAsset(asset: *Asset) void {
-    switch (asset.data) {
-        .texture => {
-            Graphics.unloadTexture(asset.data.texture.texture, asset.data.texture.sampler);
-        },
+
+    Assets.next_worker_update += 1;
+    if (Assets.next_worker_update >= WORKERS_MAX) {
+        Assets.next_worker_update = 0;
    }
-}
-pub fn get(asset: anytype) ?assetTypeFromType(@TypeOf(asset)) {
-    if (Assets.storage.get(asset.handle)) |stored| {
-        switch (@TypeOf(asset)) {
-            Texture => {
-                return stored.data.texture;
-            },
-            else => @compileError("Cannot get asset of type " ++ @typeName(@TypeOf(asset))),
+
+    Assets.free_board_mutex.lock();
+    defer Assets.free_board_mutex.unlock();
+    if (Assets.free_board.items.len == 0) return;
+
+    // TODO: Delegate freeing to worker threads?
+    Assets.asset_map_mutex.lock();
+    defer Assets.asset_map_mutex.unlock();
+    while (Assets.free_board.pop()) |request| {
+        if (@atomicLoad(usize, &request.counter, .monotonic) == 0) {
+            if (!Assets.asset_map.remove(.{ .type = request.type, .path = request.path })) continue;
+            request.unload(Game.alloc);
+            Game.alloc.destroy(request);
        }
    }
-    unreachable;
 }

-fn loadFile(alloc: std.mem.Allocator, path: []const u8) ![]u8 {
-    const file = try std.fs.cwd().openFile(path, .{});
-    defer file.close();
-    return file.readToEndAlloc(alloc, std.math.maxInt(i32));
+pub fn load(comptime asset_type: AssetType, path: []const u8) AssetContainer(asset_type.getType()) {
+    const asset = mapAsset(asset_type, path);
+    {
+        Assets.request_board_mutex.lock();
+        Assets.request_board.append(Game.alloc, asset) catch err.oom();
+        _ = @atomicRmw(usize, &Assets.request_board_counter, .Add, 1, .monotonic);
+        Assets.request_board_mutex.unlock();
+    }
+    return .{ .asset_pointer = asset };
 }
-fn typeFromAssetType(comptime asset_type: AssetType) type {
-    return switch (asset_type) {
-        .texture => Texture,
+
+pub fn free(asset: anytype) void {
+    const prev = @atomicRmw(usize, &asset.asset_pointer.counter, .Sub, 1, .monotonic);
+    if (prev == 1) {
+        Assets.free_board_mutex.lock();
+        Assets.free_board.append(Game.alloc, asset.asset_pointer) catch err.oom();
+        Assets.free_board_mutex.unlock();
+    }
+}
+
+fn loaderLoop(worker_id: usize) void {
+    var processed: usize = 0;
+    defer @atomicStore(bool, &Assets.workers[worker_id].running, false, .release);
+    while (true) {
+        const asset = blk: {
+            Assets.request_board_mutex.lock();
+            defer Assets.request_board_mutex.unlock();
+
+            const request = Assets.request_board.pop() orelse return;
+            _ = @atomicRmw(usize, &Assets.request_board_counter, .Sub, 1, .monotonic);
+            break :blk request;
        };
+
+        defer processed += 1;
+        asset.mutex.lock();
+        if (asset.state == .not_loaded)
+            asset.load(Game.alloc);
+        asset.mutex.unlock();
+    }
 }
-fn assetTypeFromType(comptime T: type) type {
-    return switch (T) {
-        Texture => AssetTexture,
-        else => unreachable,
+
+fn mapAsset(comptime asset_type: AssetType, path: []const u8) *AssetCell {
+    Assets.asset_map_mutex.lock();
+    defer Assets.asset_map_mutex.unlock();
+
+    const res = Assets.asset_map.getOrPut(Game.alloc, .{ .type = asset_type, .path = path }) catch err.oom();
+    if (!res.found_existing) {
+        res.value_ptr.* = Game.alloc.create(AssetCell) catch err.oom();
+        res.value_ptr.*.* = .{
+            .mutex = .{},
+            .type = asset_type,
+            .data = undefined,
+            .path = path,
+            .loader = Assets.makeLoader(asset_type.getType(), asset_type.getType().load),
+            .unloader = Assets.makeUnloader(asset_type.getType(), asset_type.getType().unload),
+            .state = .not_loaded,
+            .counter = 1,
        };
+    } else _ = @atomicRmw(usize, &res.value_ptr.*.counter, .Add, 1, .monotonic);
+    return res.value_ptr.*;
+}
+
+fn makeLoader(comptime T: type, comptime func: *const fn ([]const u8, std.mem.Allocator) LoadError!T) *const fn (*AssetCell, std.mem.Allocator) LoadError!void {
+    const Container = struct {
+        pub fn loader(cell: *AssetCell, alloc: std.mem.Allocator) LoadError!void {
+            const mem = try alloc.create(T);
+            errdefer alloc.destroy(mem);
+            mem.* = try func(cell.path, alloc);
+            cell.data = @ptrCast(mem);
+        }
+    };
+    return Container.loader;
+}
+
+fn makeUnloader(comptime T: type, comptime func: *const fn (T, std.mem.Allocator) void) *const fn (*AssetCell, std.mem.Allocator) void {
+    const Container = struct {
+        pub fn unloader(cell: *AssetCell, alloc: std.mem.Allocator) void {
+            func(@as(*T, @alignCast(@ptrCast(cell.data))).*, alloc);
+            alloc.destroy(@as(*T, @alignCast(@ptrCast(cell.data))));
+        }
+    };
+    return Container.unloader;
 }
--- a/src/assets/file.zig
+++ b/src/assets/file.zig
@@ -0,0 +1,14 @@
+const std = @import("std");
+const Assets = @import("../assets.zig");
+
+bytes: []u8,
+
+pub fn load(path: []const u8, alloc: std.mem.Allocator) Assets.LoadError!@This() {
+    const file = try std.fs.cwd().openFile(path, .{});
+    defer file.close();
+    return .{ .bytes = try file.readToEndAlloc(alloc, std.math.maxInt(i32)) };
+}
+
+pub fn unload(self: @This(), alloc: std.mem.Allocator) void {
+    alloc.free(self.bytes);
+}
--- a/src/assets/texture.zig
+++ b/src/assets/texture.zig
@@ -0,0 +1,34 @@
+const std = @import("std");
+const sdl = @import("sdl");
+const err = @import("../error.zig");
+const c = @import("../c.zig");
+const Assets = @import("../assets.zig");
+const Graphics = @import("../graphics.zig");
+
+texture: *sdl.GPUTexture,
+sampler: *sdl.GPUSampler,
+
+pub fn load(path: []const u8, alloc: std.mem.Allocator) Assets.LoadError!@This() {
+    _ = alloc;
+    var file = Assets.load(.file, path);
+    defer Assets.free(file);
+    const data = (try file.getSync()).bytes;
+
+    var x: i32 = undefined;
+    var y: i32 = undefined;
+    var z: i32 = undefined;
+    const image = c.stbi_load_from_memory(@ptrCast(data), @intCast(data.len), &x, &y, &z, 4);
+    if (image == null) err.stbi();
+    const image_slice = image[0..@intCast(x * y * z)];
+    const texture, const sampler = Graphics.loadTexture(@intCast(x), @intCast(y), image_slice);
+    c.stbi_image_free(image);
+    return .{
+        .texture = texture,
+        .sampler = sampler,
+    };
+}
+
+pub fn unload(self: @This(), alloc: std.mem.Allocator) void {
+    _ = alloc;
+    Graphics.unloadTexture(self.texture, self.sampler);
+}
--- a/src/game.zig
+++ b/src/game.zig
@@ -62,6 +62,7 @@ pub fn run() void {
            World.draw();
            Game.endDraw();
        }
+        Assets.update();
    }
 }

--- a/src/graphics.zig
+++ b/src/graphics.zig
@@ -420,9 +420,9 @@ pub fn clearDepth() void {
    sdl.PushGPUVertexUniformData(Graphics.command_buffer, 0, &Graphics.camera.matrix, 16 * 4);
 }

-pub fn drawMesh(mesh: Mesh, texture: Assets.Texture, transform: Transform) void {
+pub fn drawMesh(mesh: Mesh, texture: *Assets.Texture, transform: Transform) void {
    if (Graphics.render_pass == null) return;
-    const asset_texture = Assets.get(texture) orelse return;
+    const asset_texture = texture.get() orelse return;

    sdl.PushGPUVertexUniformData(Graphics.command_buffer, 1, &transform.matrix(), 16 * 4);
    sdl.BindGPUFragmentSamplers(Graphics.render_pass, 0, &sdl.GPUTextureSamplerBinding{
--- a/src/world.zig
+++ b/src/world.zig
@@ -91,6 +91,7 @@ pub fn initDebug() void {
        };
        World.object_map.put(Game.alloc, @intCast(i), i) catch err.oom();
    }
+    Assets.free(Assets.load(.texture, "data/yakuza.png"));

    World.plane_mesh = Graphics.loadMesh(@ptrCast(&PLANE_MESH_DATA));
    World.cube_mesh = Graphics.loadMesh(@ptrCast(&CUBE_MESH_DATA));
@@ -323,16 +324,16 @@ pub fn updateObject(object: *Object, delta: f32) void {
 }

 pub fn draw() void {
-    Graphics.drawMesh(World.table_mesh, World.texture, .{});
+    Graphics.drawMesh(World.table_mesh, &World.texture, .{});

    for (World.objects.items) |*object| {
        if (object.parent != .dock)
-            Graphics.drawMesh(object.mesh, object.texture, object.drawingTransform());
+            Graphics.drawMesh(object.mesh, &object.texture, object.drawingTransform());
    }

    Graphics.drawMesh(
        World.plane_mesh,
-        World.hand_texture,
+        &World.hand_texture,
        Graphics.Transform.combineTransforms(
            .{
                .position = .{ World.hand_scale * 0.5, -World.hand_scale * 0.5, 0 },
@@ -345,7 +346,7 @@ pub fn draw() void {
    Graphics.clearDepth();
    for (World.objects.items) |*object| {
        if (object.parent == .dock)
-            Graphics.drawMesh(object.mesh, object.texture, object.drawingTransform());
+            Graphics.drawMesh(object.mesh, &object.texture, object.drawingTransform());
    }
 }