Functional hot reloading

Makefile

@@ -1,8 +1,8 @@
 INTERFACEDIR:=$(shell pkg-config --variable=pkgdatadir wayland-protocols)
-CFLAGS=-Wall -Wextra -Og -ggdb3 -Wno-unused-but-set-variable -Wno-unused-parameter
+CFLAGS=-Wall -Wextra -Og -ggdb3 -Wno-unused-but-set-variable -Wno-unused-parameter -Wl,--export-dynamic
 LIBS=-lwayland-client -lwayland-egl -lEGL -lOpenGL -lxkbcommon -levdev
-wayland: wayland.c xdg-shell-protocol.c xdg-shell-client-protocol.h zwp-text-input-unstable-v3-client-protocol.c zwp-text-input-unstable-v3-protocol.h xdg-decoration-unstable-v1.c xdg-decoration-unstable-v1.h
-	gcc $(CFLAGS) $(LIBS) wayland.c xdg-shell-protocol.c xdg-decoration-unstable-v1.c zwp-text-input-unstable-v3-client-protocol.c -o wayland
+wayland: wayland.c xdg-shell-protocol.c xdg-shell-client-protocol.h zwp-text-input-unstable-v3-client-protocol.c zwp-text-input-unstable-v3-protocol.h xdg-decoration-unstable-v1.c xdg-decoration-unstable-v1.h game.h
+	gcc $(CFLAGS) $(LIBS) $^ -o wayland
 
 # TODO: Normalize these annoying names
 xdg-shell-protocol.c:
@@ -18,4 +18,4 @@ xdg-decoration-unstable-v1.c:
 xdg-decoration-unstable-v1.h:
 	wayland-scanner client-header $(INTERFACEDIR)/unstable/xdg-decoration/xdg-decoration-unstable-v1.xml xdg-decoration-unstable-v1.h
 game.so: game.c game.h
-	gcc $(CFLAGS) game.c --shared -o game.so
+	gcc $(CFLAGS) game.c -shared -o game.so

game.c

@@ -3,5 +3,5 @@
 void simulate_frame(game_state_t *state)
 {
     // TODO: Do something amazing here
-    ;
+    state->version = 1;
 }

game.h

@@ -11,6 +11,7 @@ typedef struct {
     int32_t window_w;
     int64_t frame;
     double dt;
+    int32_t version;
 } game_state_t;
 
 #endif

wayland.c

@@ -18,6 +18,7 @@
 #include <fcntl.h>
 #include <errno.h>
 #include <dlfcn.h>
+#include <sys/stat.h>
 // libevdev
 #include <libevdev-1.0/libevdev/libevdev.h>
 // generated header using wayland-scanner
@@ -70,12 +71,14 @@ error_level_t error_verbosity = { ERROR_LEVEL_DEBUG };
 
 typedef void (*simulate_frame_fn)(game_state_t*);
 
-/* Game layer */
+/* Game layer and hot reload */
 typedef struct {
     simulate_frame_fn simulate_frame;
 } game_api_t;
 
 game_api_t game_api = {};
+time_t hr_timestamp = 0;
+void *dlhandle = NULL;
 
 char *egl_s(int code)
 {
@@ -742,16 +745,25 @@ int main()
     wl_surface_commit(surface);
 
     // Trying to link with game layer
-    void *dlhandle = dlopen("./game.so", RTLD_NOW);
+    dlhandle = dlopen("./game.so", RTLD_NOW | RTLD_LOCAL);
+
     if (!dlhandle)
+    {
         console_err_ss(MODULE_HOTRELOAD, "Could not load game layer\n");
         dlerror();
+    }
 
+    struct stat fs;
+    if (stat("./game.so", &fs) == -1)
+        console_err_ss(MODULE_HOTRELOAD, "Could not get info for game library: %s\n", strerror(errno));
+
+    {
+        hr_timestamp = fs.st_mtime;
         game_api.simulate_frame = (simulate_frame_fn)dlsym(dlhandle, "simulate_frame");
-
         char *dlerr = NULL;
         if ((dlerr = dlerror()))
             console_err_ss(MODULE_HOTRELOAD, "Could not link game layer: %s\n", dlerr);
+    }
 
     // Main event loop
     int framecount = 0;
@@ -759,6 +771,37 @@ int main()
     {
         wl_display_dispatch_pending(display);
 
+        // TODO: Do not try to hot-reload every frame. Lmao
+        struct stat file_stats;
+        if (stat("./game.so", &file_stats) == -1)
+        {
+            console_err_ss(MODULE_HOTRELOAD, "Could not get info for game library: %s\n", strerror(errno));
+        }
+        else if (hr_timestamp < file_stats.st_mtime)
+        {
+            console_log_ss(MODULE_HOTRELOAD, "Game library has changed: trying to hot reload\n");
+
+            // NOTE: We cannot load new symbols from the same path unless we close the currently open handle.
+            //       However, until the linker is done with the file it will fail on dlopen.
+            //       For now we just busywait trying to link it.
+            dlclose(dlhandle);
+            while (!(dlhandle = dlopen("./game.so", RTLD_NOW | RTLD_LOCAL)));
+
+
+            hr_timestamp = fs.st_mtime;
+            game_api.simulate_frame = (simulate_frame_fn)dlsym(dlhandle, "simulate_frame");
+            char *dlerr = NULL;
+            if ((dlerr = dlerror()))
+                console_err_ss(MODULE_HOTRELOAD, "Could not link game layer: %s\n", dlerr);
+
+            hr_timestamp = file_stats.st_mtime;
+            char *error_string = dlerror();
+            if (error_string)
+                console_err_ss(MODULE_HOTRELOAD, "Error loading game code: %s\n", error_string);
+
+            console_log_ss(MODULE_HOTRELOAD, "Successfully hot reloaded game layer\n");
+        }
+
         /* Controller input handling */
         if (libevdev_get_fd(libevdev) != -1) // check if we actually found a controller to query
         {
@@ -848,8 +891,9 @@ int main()
         game_state.frame = framecount;
         // TODO: Get delta time since last frame
         game_state.dt = 0;
-
         game_api.simulate_frame(&game_state);
+        if (game_state.version != 1)
+            console_debug_ss(MODULE_HOTRELOAD, "Version %d\n", game_state.version);
         //console_debug_ss(MODULE_WAYLAND, "Frame %d\n", framecount);
         glClearColor(0.5, 0.3, 0.0, 1.0);
         glClear(GL_COLOR_BUFFER_BIT);