Initial version of single binary hot-reloading

compile/build.odin

@@ -32,8 +32,6 @@ PROJECT_NAME :: "sindri"
 BUILD_DIRECTORY :: "out/"
 
 GAME_SRC_DIR :: "game/"
-GAME_LIB_PATH :: BUILD_DIRECTORY + "game" + LIB_EXT
-GAME_LIB_TMP_PATH :: BUILD_DIRECTORY + "game_tmp" + LIB_EXT
 
 ENGINE_DIR :: "src/"
 ENGINE_OUTPUT :: BUILD_DIRECTORY + PROJECT_NAME
@@ -47,6 +45,7 @@ Options :: struct {
 	debug:        bool `args:"optional"            usage:"Build project in debug-mode."`,
 	release:      bool `args:"optional"            usage:"Build project in release-mode."`,
 	run:          bool `args:"optional"            usage:"Run project."`,
+	hot_reload:   bool `args:"optional"            usage:"Hot-reload project."`,
 	wgpu_init:    bool `args:"optional"            usage:"Prepare wgpu-native."`,
 	wgpu_version: string `args:"optional"          usage:"Override the wgpu release version to init."`,
 	fmt:          bool `args:"optional"            usage:"Run odinfmt."`,
@@ -77,6 +76,7 @@ main :: proc() {
 	if opts.debug do build_project(true, opts.overflow[:])
 	if opts.release do build_project(false, opts.overflow[:])
 	if opts.run do run_project(opts.overflow[:])
+	if opts.hot_reload do hot_reload(!opts.release, opts.overflow[:])
 	if opts.wgpu_init do wgpu_init(opts.wgpu_version)
 	if opts.fmt do format_source()
 	if opts.pre_commit do pre_commit()
@@ -91,17 +91,12 @@ main :: proc() {
 // Build project
 
 // Build the game library ('game/') and the engine ('src/')
-build_project :: proc(debug: bool, odin_extra_args: []string) {
+build_project :: proc(debug: bool, extra_args: []string) {
 	version := project_version()
 
 	// Setup compiled wgpu binary
 	wgpu_init()
 
-	// ----------------------------------------
-	// Game compile
-
-	build_game(debug, version, odin_extra_args)
-
 	// ----------------------------------------
 	// Engine compile
 
@@ -111,7 +106,7 @@ build_project :: proc(debug: bool, odin_extra_args: []string) {
 		return
 	}
 
-	build_engine(debug, version, odin_extra_args)
+	build_engine(debug, version, extra_args)
 }
 
 // Shared builder between game/engine
@@ -124,6 +119,7 @@ build_common :: proc(
 	b := brokkr.builder_make()
 	brokkr.build(&b, dir)
 	brokkr.append(&b, "-show-timings")
+	brokkr.collection(&b, "game", ".")
 	brokkr.collection(&b, PROJECT_NAME, "src")
 	brokkr.collection(&b, "gram", "vendor/gram/src")
 	brokkr.collection(&b, "wgpu", "vendor")
@@ -144,24 +140,6 @@ build_common :: proc(
 	return b
 }
 
-// Build the game as a dynamic library loaded by the engine
-build_game :: proc(debug: bool, version: string, extra_args: []string) {
-	b := build_common(GAME_SRC_DIR, debug, version, extra_args)
-	defer brokkr.builder_destroy(&b)
-	brokkr.mode(&b, .Dynamic)
-	// Use a temp file because it first writes an empty file, which the engine
-	// would load before it is actually fully written
-	brokkr.out(&b, GAME_LIB_TMP_PATH)
-	if err := brokkr.execute(&b); err != nil {
-		os.exit(1)
-	}
-
-	if !os.is_file(GAME_LIB_TMP_PATH) {
-		die("build produced no game lib %q", GAME_LIB_TMP_PATH)
-	}
-	os.rename(GAME_LIB_TMP_PATH, GAME_LIB_PATH)
-}
-
 // Build the engine executable
 build_engine :: proc(debug: bool, version: string, extra_args: []string) {
 	b := build_common(ENGINE_DIR, debug, version, extra_args)
@@ -174,8 +152,7 @@ build_engine :: proc(debug: bool, version: string, extra_args: []string) {
 
 run_project :: proc(extra_args: []string) {
 	// Build project if it wasnt already
-	if !os.exists(ENGINE_OUTPUT) ||
+	if !os.exists(output_path(ENGINE_OUTPUT)) do build_project(true, {})
-	   !os.exists(GAME_LIB_PATH) { build_project(true, {}) }
 
 	cmd := []string{output_path(ENGINE_OUTPUT)}
 	line := slice.concatenate(
@@ -206,6 +183,34 @@ run_project :: proc(extra_args: []string) {
 	os.exit(res.exit_code)
 }
 
+hot_reload :: proc(debug: bool, extra_args: []string) {
+	if engine_is_running() {
+		process := output_path(PROJECT_NAME)
+		when ODIN_OS == .Windows {
+			// Ask process to shut down gracefully (equivalent to SIGTERM)
+			_, ok, _ := exec([]string{"taskkill", "/IM", process + ".exe"})
+			if !ok {
+				die("hot reload: failed to terminate running %s", process)
+			}
+		} else {
+			_, ok, _ := exec([]string{"pkill", "-TERM", "-x", process})
+			if !ok {
+				die(
+					"hot reload: failed to send SIGTERM to running %s",
+					process,
+				)
+			}
+		}
+
+		// Wait for process to terminate
+		for engine_is_running() {
+			time.sleep(time.Millisecond * 20)
+		}
+	}
+
+	run_project(extra_args)
+}
+
 // -----------------------------------------
 // wgpu setup
 

docs/hot-reloading.md

@@ -0,0 +1,47 @@
+# Hot Reloading
+
+Instead of having the engine as an exe and game as a dll, and having to jump
+through hoops to share libraries internal state between them we do it
+differently. The engine and game live in the same binary, compiled fully each
+time. We rely mostly on static memory, and register these memory regions. Then
+when we want to hot reload: we send a close signal to the running instance, it
+writes a snapshot of the active memory to disk, instance closes, recompile,
+restart the application, it restores the memory from the snapshot.
+
+## Byte Layout On Disk
+
+```odin
+Snapshot_Header :: struct #packed #all_or_none {
+	magic_string:     u32,
+	version:          u16, // spec of the snapshot
+    app_version:      [4 + time.MIN_YYYY_DATE_LEN + 8]u8, // example: `dev-2026-09-23-a4084b3`
+    region_count:     u32,
+}
+
+Region_Header :: struct #packed #all_or_none {
+	name_size: u32,
+	data_size: u32,
+}
+```
+
+[ Snapshot_Header  ]
+[ Region_Header    ]
+[   name bytes     ]
+[   data bytes     ]
+[ Region_Header    ]
+[   name bytes     ]
+[   data bytes     ]
+[ etc..            ]
+
+## Diff Checking
+
+Use hashing per memory segment to do a sanity diff-check.
+
+```odin
+import "core:crypto/hash"
+
+data: []byte = ...
+
+digest := hash.hash_bytes(hash.Algorithm.SHA256, data)
+defer delete(digest)
+```

game/game.odin

@@ -7,39 +7,42 @@ import "sindri:base"
 import "sindri:core"
 
 // -----------------------------------------
+// Types
 
 Game_Memory :: struct {
 	should_close: bool,
 }
 
-g: ^Game_Memory
+Test_Memory :: struct {
+	asd: int,
+	qwe: int,
+}
 
 // -----------------------------------------
+// Variables
 
-@(export)
+g: Game_Memory
-memory :: proc() -> rawptr {
+t: Test_Memory
-	return g
+
+game_api := core.Game_API {
+	settings      = settings,
+	init_once     = init_once,
+	init          = init,
+	update        = update,
+	render        = render,
+	destroy       = destroy,
+	should_close  = should_close,
+	force_reload  = force_reload,
+	force_restart = force_restart,
 }
 
-@(export)
+// -----------------------------------------
-memory_free :: proc() {
+// Public functions
-	free(g)
+
+api :: proc() -> ^core.Game_API {
+	return &game_api
 }
 
-@(export)
-memory_size :: proc() -> int {
-	return size_of(Game_Memory)
-}
-
-@(export)
-memory_set :: proc(mem: rawptr) {
-	g = (^Game_Memory)(mem)
-
-	// Here you can also set your own global variables. A good idea is to make
-	// your global variables into pointers that point to something inside `g`.
-}
-
-@(export)
 settings :: proc() -> base.Settings {
 	return base.Settings {
 		width = 960,
@@ -51,36 +54,40 @@ settings :: proc() -> base.Settings {
 	}
 }
 
-@(export)
 init_once :: proc() {
 	fmt.println("init once")
+
+	base.register_region("game_memory", &g, size_of(Game_Memory))
+	base.register_region("test_memory", &t, size_of(Test_Memory))
 }
 
-@(export)
 init :: proc() {
 	fmt.println("hello from .dll!")
 
-	g = new(Game_Memory)
+	g.should_close = false
-	memory_set(g)
 }
 
-@(export)
 update :: proc(dt: f32) {
 	fmt.println("dt:", dt)
 
 	if core.key_state(.Key_Escape) == .Press {
 		g.should_close = true
 	}
+
+	if core.key_state(.Key_F5) == .Press do t.asd = 555
+	if core.key_state(.Key_F6) == .Press do t.asd = 666
 }
 
-@(export)
+render :: proc() {  }
+
 destroy :: proc() {
 	fmt.println("bye")
+
+	fmt.println(t.asd, t.qwe)
 }
 
 start := time.tick_now()
 
-@(export)
 should_close :: proc() -> bool {
 	elapsed := time.tick_since(start)
 	seconds := time.duration_seconds(elapsed)
@@ -89,12 +96,10 @@ should_close :: proc() -> bool {
 	return g.should_close
 }
 
-@(export)
 force_reload :: proc() -> bool {
 	return core.key_state(.Key_F5) == .Press
 }
 
-@(export)
 force_restart :: proc() -> bool {
 	return core.key_state(.Key_F6) == .Press
 }

ols.json

@@ -1,7 +1,8 @@
 {
     "collections": [
+        { "name": "game",   "path": "." },
         { "name": "sindri", "path": "src" },
         { "name": "gram",   "path": "vendor/gram/src" },
-        { "name": "wgpu",    "path": "vendor" }
+        { "name": "wgpu",   "path": "vendor" }
     ]
 }

src/base/base.odin

@@ -0,0 +1,3 @@
+package base
+
+should_close: bool

src/base/event.odin

@@ -158,8 +158,6 @@ on_event :: proc(data: Event_Data) {
 drain_event_queue :: proc() {
 	assert(event_bus.queue != nil)
 
-	fmt.println("toby!")
-
 	for &event in event_bus.queue {
 
 		#partial switch e in event.data {

src/base/hot_reload.odin

@@ -1,231 +1,302 @@
 package base
 
-import "core:c"
+import "base:runtime"
-import "core:dynlib"
+import "core:crypto/hash"
 import "core:fmt"
+import "core:mem"
 import "core:os"
+import "core:strings"
 import "core:time"
 
-when ODIN_OS == .Windows {
+SNAPSHOT_NAME :: "snapshot"
-	LIB_EXT :: ".dll"
+SNAPSHOT_EXTENSION :: "sndr"
-} else when ODIN_OS == .Darwin {
-	LIB_EXT :: ".dylib"
-} else {
-	LIB_EXT :: ".so"
-}
 
-GAME_LIB_DIR :: "out/"
+MAGIC_STRING :: 0x72646E73 // "rdns" -> "sndr" in little endian
-GAME_LIB_PATH :: GAME_LIB_DIR + "game" + LIB_EXT
+HOT_RELOAD_VERSION :: 1
+APP_VERSION_SIZE :: 4 + time.MIN_YYYY_DATE_LEN + 8 + 6 // example: `dev-2026-09-23-a4084b3-debug`
 
 // -----------------------------------------
+// Types
 
+@(private)
+Snapshot_Header :: struct #packed #all_or_none {
+	magic_string: u32,
+	version:      u16, // spec of the snapshot
+	app_version:  [APP_VERSION_SIZE]u8,
+	region_count: u32,
+}
+
+@(private)
+Region_Header :: struct #packed #all_or_none {
+	name_size: u32,
+	data_size: u32,
+}
+
+@(private)
+Memory_Region :: struct {
+	ptr_location: rawptr,
+	// TODO: How do we do hash compare without having to hash current memory every frame?
+	digest:       []u8, // hash of this region in last snapshot
+}
+
+@(private)
 Hot_Reload :: struct {
-	loaded_libs: [dynamic]Game_API,
+	allocator:           runtime.Allocator,
-}
+	snapshot_path:       string,
-
+	snapshot_header:     Snapshot_Header,
-Hot_Reload_Error :: enum u8 {
+	region_headers:      map[string]Region_Header, // hash of name:size
-	None                 = 0,
+	regions:             map[string]Memory_Region, // hash of name:size
-	Load_Game_Lib_Failed = 1,
+	write_full_snapshot: bool,
-	Unimplemented        = 127,
-	Okay                 = None,
-}
-
-Error :: union #shared_nil {
-	Hot_Reload_Error,
-}
-
-Game_API :: struct {
-	lib:               dynlib.Library,
-	memory:            proc() -> rawptr,
-	memory_free:       proc(),
-	memory_size:       proc() -> int,
-	memory_set:        proc(mem: rawptr),
-	settings:          proc() -> Settings,
-	init_once:         proc(),
-	init:              proc(),
-	update:            proc(_: f32),
-	render:            proc(),
-	destroy:           proc(),
-	should_close:      proc() -> bool,
-	force_reload:      proc() -> bool,
-	force_restart:     proc() -> bool,
-	modification_time: time.Time,
-	api_version:       int, // iteration of the game lib
 }
 
 // -----------------------------------------
+// Variables
 
-hot_reload_init :: proc() -> (hr: Hot_Reload, error: Error) {
+@(private)
-	api: Game_API
+hr: Hot_Reload
-
-	api_ok := load_game_lib(&api)
-	if !api_ok {
-		fmt.println("error: failed to load Game API")
-		return {}, .Load_Game_Lib_Failed
-	}
-
-	hr.loaded_libs = make([dynamic]Game_API, 0, 0, context.allocator)
-	append(&hr.loaded_libs, api)
-
-	return hr, nil
-}
-
-hot_reload_destroy :: proc(state: ^Hot_Reload) {
-	for &api in state.loaded_libs {
-		unload_game_lib(&api)
-	}
-
-	delete(state.loaded_libs)
-}
 
 // -----------------------------------------
+// Constructor & destructor
 
-active_lib :: proc(hr: ^Hot_Reload) -> ^Game_API {
+hot_reload_init :: proc(
-	return &hr.loaded_libs[len(hr.loaded_libs) - 1]
+	app_version: string,
-}
+	allocator := context.allocator,
-
+) -> os.Error {
-should_close :: proc(hr: ^Hot_Reload) -> bool {
+	// Get snapshot path
-	api := active_lib(hr)
+	out := os.get_executable_directory(allocator) or_return
-	if api.lib == nil do return true
+	defer delete(out, allocator)
-	return api.should_close()
+	snapshot_path := fmt.tprintf(
-}
+		"%v/%v.%v",
-
+		out,
-copy_lib :: proc(to: string) -> bool {
+		SNAPSHOT_NAME,
-	copy_err := os.copy_file(to, GAME_LIB_PATH)
+		SNAPSHOT_EXTENSION,
-	if copy_err != nil {
-		fmt.printfln(
-			"error: failed to copy {0} to {1}: {2:v}",
-			GAME_LIB_PATH,
-			to,
-			copy_err,
-		)
-		return false
-	}
-
-	return true
-}
-
-// Load game lib symbols
-load_game_lib :: proc(api: ^Game_API) -> bool {
-	mod_time, mod_time_err := os.last_write_time_by_name(GAME_LIB_PATH)
-	if mod_time_err != os.ERROR_NONE {
-		fmt.printfln(
-			"error: failed getting last write time of {0}, error code: {1}",
-			GAME_LIB_PATH,
-			mod_time_err,
-		)
-		return false
-	}
-	api.modification_time = mod_time
-
-	lib_name := fmt.tprintf(
-		GAME_LIB_DIR + "game_{0}" + LIB_EXT,
-		api.api_version,
 	)
-	copy_lib(lib_name) or_return
+	snapshot_path_cpy := strings.clone(snapshot_path, allocator)
 
-	// Match the names of the fields in Game_API to symbols in the game DLL
+	// Copy version string
-	_, ok := dynlib.initialize_symbols(api, lib_name, "", "lib")
+	version: [APP_VERSION_SIZE]u8
-	if !ok {
+	n := min(len(app_version), APP_VERSION_SIZE)
-		fmt.printfln(
+	copy(version[:n], app_version[:n])
-			"error: failed initializing symbols: {0}",
+
-			dynlib.last_error(),
+	hr = {
+		allocator = allocator,
+		snapshot_path = snapshot_path_cpy,
+		snapshot_header = {
+			magic_string = MAGIC_STRING,
+			version = HOT_RELOAD_VERSION,
+			app_version = version,
+			region_count = 0,
+		},
+		region_headers = make(map[string]Region_Header, 1, allocator), // initial capacity for nil checks
+		regions = make(map[string]Memory_Region, 1, allocator), // initial capacity for nil checks
+		write_full_snapshot = true,
+	}
+
+	return nil
+}
+
+hot_reload_destroy :: proc() {
+	assert(
+		hr.region_headers != nil,
+		"[hot-reload] destroying uninitialized data",
+	)
+
+	assert(hr.regions != nil, "[hot-reload] destroying uninitialized data")
+
+	delete(hr.snapshot_path, hr.allocator)
+
+	for key, region in hr.region_headers do delete(key, hr.allocator)
+	for key, region in hr.regions {
+		if region.digest != nil do delete(region.digest, hr.allocator)
+	}
+
+	delete(hr.region_headers)
+	delete(hr.regions)
+}
+
+// -----------------------------------------
+// Public functions
+
+register_region :: proc(
+	name: string,
+	ptr_location: rawptr,
+	data_size: u32,
+) -> os.Error {
+	assert(hr.region_headers != nil, "[hot-reload] uninitialized")
+	assert(hr.regions != nil, "[hot-reload] uninitialized")
+	assert(ptr_location != nil, "[hot_reload] invalid location")
+	assert(data_size > 0, "[hot_reload] invalid type size")
+
+	hash := fmt.tprintf("%v:%d", name, data_size)
+	assert(!(hash in hr.regions), "[hot_reload] double registration")
+	hash_cpy := strings.clone(hash, hr.allocator)
+	hr.region_headers[hash_cpy] = Region_Header {
+		name_size = cast(u32)len(name),
+		data_size = data_size,
+	}
+	hr.regions[hash_cpy] = Memory_Region {
+		ptr_location = ptr_location,
+	}
+
+	hr.snapshot_header.region_count += 1
+
+	hr.write_full_snapshot = true
+
+	return nil
+}
+
+read_snapshot :: proc() -> os.Error {
+	assert(hr.region_headers != nil, "[hot-reload] uninitialized")
+	assert(hr.regions != nil, "[hot-reload] uninitialized")
+
+	if !os.exists(hr.snapshot_path) {
+		hr.write_full_snapshot = true
+		return nil
+	}
+
+	snapshot := os.open(hr.snapshot_path, {.Read}) or_return
+	defer os.close(snapshot)
+
+	offset: i64
+
+	// Read snapshot header
+	snapshot_header: Snapshot_Header
+	header_bytes := mem.ptr_to_bytes(&snapshot_header)
+	os.read_at(snapshot, header_bytes, offset) or_return
+	offset += size_of(Snapshot_Header)
+	assert(
+		snapshot_header.magic_string == MAGIC_STRING,
+		"[hot-reload] unknown filetype",
+	)
+	assert(
+		snapshot_header.version == HOT_RELOAD_VERSION,
+		"[hot-reload] incompatible snapshot version",
+	)
+
+	region_header: Region_Header
+	for i in 0 ..< snapshot_header.region_count {
+
+		// Read region header
+		header_bytes := mem.ptr_to_bytes(&region_header)
+		os.read_at(snapshot, header_bytes, offset) or_return
+		offset += size_of(Region_Header)
+
+		// Read region name
+		name_bytes := make([]byte, region_header.name_size, hr.allocator)
+		defer delete(name_bytes, hr.allocator)
+		os.read_at(snapshot, name_bytes, offset) or_return
+		offset += cast(i64)region_header.name_size
+		name := transmute(string)name_bytes[:]
+
+		// Read region data
+		data_bytes := make([]byte, region_header.data_size, hr.allocator)
+		defer delete(data_bytes, hr.allocator)
+		os.read_at(snapshot, data_bytes, offset) or_return
+		offset += cast(i64)region_header.data_size
+
+		// Compare currently registered region with the loaded region
+		key := fmt.tprintf("%v:%d", name, region_header.data_size)
+		new_region_header, ok := hr.region_headers[key]
+		if !ok || region_header.data_size != new_region_header.data_size {
+			hr.write_full_snapshot = true
+			fmt.println("[hot-reload] bail loading region:", name)
+			continue
+		}
+
+		// Create digest and store in registered regions
+		digest := hash.hash_bytes(
+			hash.Algorithm.SHA256,
+			data_bytes,
+			hr.allocator,
 		)
-	} else {
+		region := &hr.regions[key]
-		// Odin's shared libraries don't register a constructor, so the lib's
+		region.digest = digest
-		// runtime init (@init procs like os.stdout setup) never runs on load.
-		// Call it explicitly.
-		// Windows doesn't need this: its dynamic build exports DllMain, which
-		// the OS calls on load and which runs _startup_runtime itself.
-		when ODIN_OS != .Windows {
-			Entry :: #type proc "c" () -> c.int
-			entry_ptr, entry_ok := dynlib.symbol_address(
-				api.lib,
-				"_odin_entry_point",
-			)
-			if entry_ok do (transmute(Entry)entry_ptr)()
-		}
-	}
 
-	return ok
+		// Write snapshot memory to the memory region
-}
+		dest := mem.byte_slice(
-
+			region.ptr_location,
-// Unload game lib, used during full restarts
+			cast(int)region_header.data_size,
-unload_game_lib :: proc(api: ^Game_API) {
-	if api.lib != nil {
-		if !dynlib.unload_library(api.lib) {
-			fmt.eprintfln(
-				"error: failed unloading lib: {0}",
-				dynlib.last_error(),
-			)
-		}
-	}
-
-	if os.remove(
-		   fmt.tprintf(GAME_LIB_DIR + "game_{0}" + LIB_EXT, api.api_version),
-	   ) !=
-	   nil {
-		fmt.printfln(
-			"error: failed to remove {0}game_{1}{2} copy",
-			GAME_LIB_DIR,
-			api.api_version,
-			LIB_EXT,
 		)
+		copy(dest, data_bytes)
 	}
+
+	return nil
 }
 
-reload_game_lib :: proc(hr: ^Hot_Reload) -> (lib: ^Game_API, err: Error) {
+// Next write will be a full memory snapshot
-	api := active_lib(hr)
+set_write_full_snapshot :: proc() {
-	force_reload := api.force_reload()
+	hr.write_full_snapshot = true
-	force_restart := api.force_restart()
+}
-	reload := force_reload || force_restart
 
-	lib_mod, lib_mod_err := os.last_write_time_by_name(GAME_LIB_PATH)
+// Write memory snapshot, save on writes by diff-ing
-	// TODO: Handle error
+write_snapshot :: proc() -> os.Error {
-	if lib_mod_err == os.ERROR_NONE && api.modification_time != lib_mod {
+	assert(hr.region_headers != nil, "[hot-reload] uninitialized")
-		reload = true
+	assert(hr.regions != nil, "[hot-reload] uninitialized")
-	}
 
-	if !reload do return api, nil
+	snapshot: ^os.File
-
+	if hr.write_full_snapshot || !os.exists(hr.snapshot_path) {
-	new_api: Game_API
+		snapshot = os.create(hr.snapshot_path) or_return
-	new_api.api_version = api.api_version + 1
-	new_api_ok := load_game_lib(&new_api)
-	if !new_api_ok {
-		fmt.println("error: failed to load Game API")
-		return nil, .Load_Game_Lib_Failed
-	}
-
-	force_restart = force_restart || api.memory_size() != new_api.memory_size()
-
-	if !force_restart {
-		// This does the normal hot reload
-
-		// Note that we don't unload the old game APIs because that
-		// would unload the lib. The lib can contain stored info
-		// such as string literals. The old libs are only unloaded
-		// on a full reset or on shutdown.
-		memory := api.memory()
-		new_api.memory_set(memory)
 	} else {
-		// This does a full reset. That's basically like opening and
+		snapshot = os.open(hr.snapshot_path, {.Read, .Write}) or_return
-		// closing the game, without having to restart the executable.
+	}
-		//
+	defer os.close(snapshot)
-		// You end up in here if the game requests a full reset OR
-		// if the size of the game memory has changed. That would
-		// probably lead to a crash anyways.
 
-		api.memory_free()
+	offset: i64
 
-		for &g in hr.loaded_libs {
+	// Write header
-			unload_game_lib(&g)
+	if hr.write_full_snapshot {
+		header_bytes := mem.ptr_to_bytes(&hr.snapshot_header)
+		n := os.write_at(snapshot, header_bytes, offset) or_return
+	}
+	offset += size_of(Snapshot_Header)
+
+	for key, &region in hr.regions {
+		header := hr.region_headers[key]
+
+		// Write region header
+		if hr.write_full_snapshot {
+			header_bytes := mem.ptr_to_bytes(&header)
+			os.write_at(snapshot, header_bytes, offset) or_return
 		}
-		clear(&hr.loaded_libs)
+		offset += size_of(Region_Header)
 
-		new_api.init()
+		// Write region name
+		if hr.write_full_snapshot {
+			name := key[:header.name_size] // get name from first part of the hash
+			name_bytes := transmute([]byte)name
+			os.write_at(snapshot, name_bytes, offset) or_return
+		}
+		offset += cast(i64)header.name_size
+
+		// Write region data (if bytes differ)
+		data_bytes := mem.byte_slice(region.ptr_location, header.data_size)
+		digest := hash.hash_bytes(
+			hash.Algorithm.SHA256,
+			data_bytes,
+			hr.allocator,
+		)
+		if hr.write_full_snapshot || mem.compare(digest, region.digest) != 0 {
+			delete(region.digest, hr.allocator)
+			region.digest = digest
+			os.write_at(snapshot, data_bytes, offset) or_return
+		} else {
+			delete(digest, hr.allocator)
+		}
+		offset += cast(i64)header.data_size
 	}
 
-	append(&hr.loaded_libs, new_api)
+	hr.write_full_snapshot = false
 
-	return active_lib(hr), nil
+	return nil
+}
+
+force_reload :: proc() {
+	should_close = true
+}
+
+force_restart :: proc() -> os.Error {
+	should_close = true
+	os.remove(hr.snapshot_path) or_return
+
+	return nil
 }

src/core/api.odin

@@ -0,0 +1,18 @@
+package core
+
+import "sindri:base"
+
+// -----------------------------------------
+// Types
+
+Game_API :: struct {
+	settings:      proc() -> base.Settings,
+	init_once:     proc(),
+	init:          proc(),
+	update:        proc(dt: f32),
+	render:        proc(),
+	destroy:       proc(),
+	should_close:  proc() -> bool,
+	force_reload:  proc() -> bool,
+	force_restart: proc() -> bool,
+}

src/main.odin

@@ -3,6 +3,7 @@ package sindri
 import "core:fmt"
 import "core:time"
 
+import "game:game"
 import "sindri:base"
 import "sindri:platform"
 
@@ -14,8 +15,13 @@ main :: proc() {
 	fmt.println("hello world!", VERSION)
 
 	// Hot reload development functionality
-	hr, err := base.hot_reload_init()
+	base.hot_reload_init(VERSION)
-	defer base.hot_reload_destroy(&hr)
+	defer base.hot_reload_destroy()
+
+	// Load game API & settings
+	api := game.api()
+	defer api.destroy()
+	settings := api.settings()
 
 	// Event system
 	base.event_bus_init()
@@ -23,8 +29,9 @@ main :: proc() {
 
 	base.event_subscribe(base.Key_Press_Event, test)
 
-	api := base.active_lib(&hr)
+	// Listen for OS signals (SIGINT, SIGTERM)
-	settings := api.settings()
+	platform.signals_init()
+	defer platform.signals_destroy()
 
 	// Initialize Window
 	platform.os_init(settings)
@@ -36,29 +43,41 @@ main :: proc() {
 	defer platform.instance_destroy()
 
 	api.init_once()
+
+	base.read_snapshot()
+
 	api.init()
 
-	gt: f64 = 0
+	dt: f64
-	dt: f32
+	gt: f64
+	st: f64
+
+	for !api.should_close() &&
+	    !platform.os_should_close() &&
+	    !base.should_close {
 
-	for !platform.os_should_close() && !base.should_close(&hr) {
 		start := time.tick_now()
 
 		platform.os_poll_events()
 		base.drain_event_queue()
-		api.update(dt)
+		api.update(cast(f32)dt)
+		base.write_snapshot()
 
-		platform.frame(dt)
+		platform.frame()
+		api.render()
 
-		dt = f32(time.duration_seconds(time.tick_since(start)))
+		dt = time.duration_seconds(time.tick_since(start))
-		gt += f64(dt)
+		gt += dt
+		st += dt
 
-		// Hot reload
+		if st > 5 {
-		api, err = base.reload_game_lib(&hr)
+			st -= 5
-		if err != nil do break
+			base.set_write_full_snapshot()
+		}
+
+		if api.force_reload() do base.force_reload()
+		if api.force_restart() do base.force_restart()
 	}
-
-	api.destroy()
 }
 
 test :: proc(e: ^base.Key_Press_Event, _: rawptr) -> bool {

src/platform/glfw.odin

@@ -1,5 +1,6 @@
 package platform
 
+import "base:intrinsics"
 import "core:fmt"
 import "core:strings"
 import "vendor:glfw"
@@ -113,7 +114,8 @@ os_set_callback_proc :: proc(window: rawptr) {
 }
 
 os_should_close :: proc() -> bool {
-	return bool(glfw.WindowShouldClose(state.os.window))
+	window_close := bool(glfw.WindowShouldClose(state.os.window))
+	return window_close || intrinsics.atomic_load(&quit_signal_received)
 }
 
 os_set_should_close :: proc(val: bool) {

src/platform/signals.odin

@@ -0,0 +1,48 @@
+package platform
+
+import "base:intrinsics"
+import "core:c/libc"
+import "core:fmt"
+
+// -----------------------------------------
+// Variables
+
+// Read with atomic_load, safe across threads / interrupt contexts
+quit_signal_received: bool
+
+// -----------------------------------------
+// Public functions
+
+// Register signal handlers
+signals_init :: proc() {
+	// SIGINT = Interrupt, typically Ctrl+C
+	if libc.signal(libc.SIGINT, signal_handler) ==
+	   cast(proc "c" (_: i32))libc.SIG_ERR {
+		fmt.eprintln("error: failed to register SIGINT handler")
+	}
+
+	// SIGTERM = Normal termination
+	if libc.signal(libc.SIGTERM, signal_handler) ==
+	   cast(proc "c" (_: i32))libc.SIG_ERR {
+		fmt.eprintln("error: failed to register SIGTERM handler")
+	}
+}
+
+// Restore default signal handlers
+signals_destroy :: proc() {
+	libc.signal(libc.SIGINT, cast(proc "c" (_: i32))libc.SIG_DFL)
+	libc.signal(libc.SIGTERM, cast(proc "c" (_: i32))libc.SIG_DFL)
+}
+
+@(private = "file")
+signal_handler :: proc "c" (sig: i32) {
+	switch sig {
+		case libc.SIGINT:
+			fallthrough
+		case libc.SIGTERM:
+			intrinsics.atomic_store(&quit_signal_received, true)
+		case:
+			context = state.ctx
+			panic("[signal] unhandled signal type")
+	}
+}

src/platform/wgpu.odin

@@ -96,7 +96,7 @@ resize :: proc "c" () {
 	wgpu.SurfaceConfigure(state.surface, &state.config)
 }
 
-frame :: proc "c" (dt: f32) {
+frame :: proc "c" () {
 	context = state.ctx
 
 	surface_texture := wgpu.SurfaceGetCurrentTexture(state.surface)