wayland: use mutexes to ensure that MwLLDestroyImpl never conflicts with wayland events.

include/Mw/LowLevel/Wayland.h

@@ -16,6 +16,7 @@
 #include <wayland-client.h>
 #include <xkbcommon/xkbcommon.h>
 #include <cairo/cairo.h>
+#include <pthread.h>
 
 MWDECL int MwLLWaylandCallInit(void);
 
@@ -191,6 +192,12 @@ struct _MwLLWayland {
 	struct _MwLLWaylandShmBuffer  cursor;
 	struct _MwLLWaylandShmBuffer* icon;
 
+	/*
+	Events mutex. Any time a keyboard/mouse event happens, we try to lock this for 100 milliseconds, then give up if we can't do it. This is used in conjunction with some code in the MwLLDestroyImpl to make sure that destroy is NEVER interferes with an ongoing event.
+
+	IOI_XD: This sounds like a hilariously rare edge case, so it's almost funnier that this happened with 100% certainty for me and I spent day(s) trying to figure out what was happening. */
+	pthread_mutex_t eventsMutex;
+
 	cairo_surface_t* cs;
 	cairo_t*	 cairo;
 };

src/backend/wayland.c

@@ -340,10 +340,18 @@ static void zwp_primary_selection_device_manager_v1_interface_destroy(struct _Mw
 static void pointer_enter(void* data, struct wl_pointer* wl_pointer, MwU32 serial,
 			  struct wl_surface* surface, wl_fixed_t surface_x,
 			  wl_fixed_t surface_y) {
-	MwLL self		     = data;
+	MwLL		self = data;
+	struct timespec t;
+	t.tv_nsec = 100;
+
+	if(pthread_mutex_timedlock(&self->wayland.eventsMutex, &t) != 0) {
+		return;
+	};
 	self->wayland.pointer_serial = serial;
 
 	wl_pointer_set_cursor(wl_pointer, serial, self->wayland.cursor.surface, 0, 0);
+
+	pthread_mutex_unlock(&self->wayland.eventsMutex);
 };
 
 /* `wl_pointer.leave` callback */
@@ -357,6 +365,12 @@ static void pointer_motion(void* data, struct wl_pointer* wl_pointer, MwU32 time
 	MwLL	  self = data;
 	MwLLMouse p;
 
+	struct timespec t;
+	t.tv_nsec = 100;
+
+	if(pthread_mutex_timedlock(&self->wayland.eventsMutex, &t) != 0) {
+		return;
+	};
 	self->wayland.cur_mouse_pos.x = wl_fixed_to_double(surface_x);
 	self->wayland.cur_mouse_pos.y = wl_fixed_to_double(surface_y);
 
@@ -364,14 +378,22 @@ static void pointer_motion(void* data, struct wl_pointer* wl_pointer, MwU32 time
 	MwLLDispatch(self, move, &p);
 
 	self->wayland.events_pending += 1;
+	pthread_mutex_unlock(&self->wayland.eventsMutex);
 
 	/*timed_redraw(self, time, 50, &self->wayland.cooldown_timer);*/
 };
 
 /* `wl_pointer.button` callback */
 static void pointer_button(void* data, struct wl_pointer* wl_pointer, MwU32 serial, MwU32 time, MwU32 button, MwU32 state) {
-	MwLL	  self = data;
+	MwLL		self = data;
-	MwLLMouse p;
+	MwLLMouse	p;
+	struct timespec t;
+	t.tv_nsec = 100;
+
+	if(pthread_mutex_timedlock(&self->wayland.eventsMutex, &t) != 0) {
+		return;
+	};
+
 	p.point = self->wayland.cur_mouse_pos;
 	if(p.point.x > self->wayland.x && p.point.x < self->wayland.x + self->wayland.ww && p.point.y > self->wayland.y && p.point.y < self->wayland.y + self->wayland.wh) {
 		switch(button) {
@@ -403,6 +425,7 @@ static void pointer_button(void* data, struct wl_pointer* wl_pointer, MwU32 seri
 		MwLLDispatch(self, draw, NULL);
 		self->wayland.events_pending += 1;
 	}
+	pthread_mutex_unlock(&self->wayland.eventsMutex);
 };
 
 /* `wl_pointer.axis` callback */
@@ -450,11 +473,19 @@ static void keyboard_enter(void*	       data,
 			   MwU32	       serial,
 			   struct wl_surface*  surface,
 			   struct wl_array*    keys) {
-	MwLL self		      = data;
+	MwLL		self = data;
+	struct timespec t;
+	t.tv_nsec = 100;
+
+	if(pthread_mutex_timedlock(&self->wayland.eventsMutex, &t) != 0) {
+		return;
+	};
+
 	self->wayland.keyboard_serial = serial;
 
 	MwLLDispatch(self, focus_in, NULL);
 	self->wayland.events_pending += 1;
+	pthread_mutex_unlock(&self->wayland.eventsMutex);
 };
 
 /* `wl_keyboard.leave` callback */
@@ -462,9 +493,18 @@ static void keyboard_leave(void*	       data,
 			   struct wl_keyboard* wl_keyboard,
 			   MwU32	       serial,
 			   struct wl_surface*  surface) {
-	MwLL self = data;
+	MwLL		self = data;
+	struct timespec t;
+	t.tv_nsec = 100;
+
+	if(pthread_mutex_timedlock(&self->wayland.eventsMutex, &t) != 0) {
+		return;
+	};
+
 	MwLLDispatch(self, focus_out, NULL);
 	self->wayland.events_pending += 1;
+
+	pthread_mutex_unlock(&self->wayland.eventsMutex);
 };
 
 /* `wl_keyboard.key` callback */
@@ -474,7 +514,13 @@ static void keyboard_key(void*		     data,
 			 MwU32		     time,
 			 MwU32		     key,
 			 MwU32		     state) {
-	MwLL self = data;
+	MwLL		self = data;
+	struct timespec t;
+	t.tv_nsec = 100;
+
+	if(pthread_mutex_timedlock(&self->wayland.eventsMutex, &t) != 0) {
+		return;
+	};
 	if(self->wayland.type == MWLL_WAYLAND_TOPLEVEL) {
 		struct _MwLLWaylandTopLevel* wayland = self->wayland.toplevel;
 		xkb_layout_index_t	     layout;
@@ -564,6 +610,8 @@ static void keyboard_key(void*		     data,
 		MwLLDispatch(self, draw, NULL);
 		self->wayland.events_pending += 1;
 	}
+
+	pthread_mutex_unlock(&self->wayland.eventsMutex);
 };
 
 /* `wl_keyboard.modifiers` callback */
@@ -574,11 +622,19 @@ static void keyboard_modifiers(void*		   data,
 			       MwU32		   mods_latched,
 			       MwU32		   mods_locked,
 			       MwU32		   group) {
-	MwLL self = data;
+	MwLL		self = data;
+	struct timespec t;
+	t.tv_nsec = 100;
+
+	if(pthread_mutex_timedlock(&self->wayland.eventsMutex, &t) != 0) {
+		return;
+	};
 
 	self->wayland.mod_state = 0;
 	self->wayland.mod_state |= mods_depressed;
 	self->wayland.mod_state |= mods_locked;
+
+	pthread_mutex_unlock(&self->wayland.eventsMutex);
 };
 
 struct wl_keyboard_listener keyboard_listener = {
@@ -1305,7 +1361,11 @@ static MwLL MwLLCreateImpl(MwLL parent, int x, int y, int width, int height) {
 }
 
 static void MwLLDestroyImpl(MwLL handle) {
-	int i;
+	int	       i;
+	struct timeval tv;
+	int	       select_ret;
+
+	pthread_mutex_lock(&handle->wayland.eventsMutex);
 
 	MwLLDestroyCommon(handle);
 
@@ -1349,6 +1409,16 @@ static void MwLLDestroyImpl(MwLL handle) {
 		wl_keyboard_destroy(handle->wayland.keyboard);
 	}
 
+	/* sleep long enough that any active attempts to wait for the mutex will have given up and we can safely unlock/destroy it */
+	tv.tv_sec  = 0;
+	tv.tv_usec = 250;
+	do {
+		select_ret = select(1, NULL, NULL, NULL, &tv);
+	} while((select_ret == -1) && (errno == EINTR));
+
+	pthread_mutex_unlock(&handle->wayland.eventsMutex);
+	pthread_mutex_destroy(&handle->wayland.eventsMutex);
+
 	free(handle);
 }
 
@@ -1465,6 +1535,7 @@ static void MwLLFreeColorImpl(MwLLColor color) {
 static int MwLLPendingImpl(MwLL handle) {
 	MwBool		pending = MwFALSE;
 	struct timespec timeout;
+	int		i;
 
 	if(handle->wayland.always_render) {
 		return event_loop(handle);