compositor: introduce weston_buffer_reference

The wl_buffer reference counting API has been inconsistent. You would
manually increment the refcount and register a destroy listener, as
opposed to calling weston_buffer_post_release(), which internally
decremented the refcount, and then removing a list item.

Replace both cases with a single function:
weston_buffer_reference(weston_buffer_reference *ref, wl_buffer *buffer)

Buffer is assigned to ref->buffer, while taking care of all the refcounting
and release posting. You take a reference by passing a non-NULL buffer, and
release a reference by passing NULL as buffer. The function uses an
internal wl_buffer destroy listener, so the pointer gets reset on
destruction automatically.

This is inspired by the pipe_resource_reference() of Mesa, and modified
by krh's suggestion to add struct weston_buffer_reference.

Additionally, when a surface gets destroyed, the associated wl_buffer
will send a release event. Often the buffer is already destroyed on
client side, so the event will be discarded by libwayland-client.

Compositor-drm.c is converted to use weston_buffer_reference.

Signed-off-by: Pekka Paalanen <ppaalanen@gmail.com>

src/compositor-drm.c

@@ -118,8 +118,7 @@ struct drm_fb {
 	struct drm_output *output;
 	uint32_t fb_id;
 	int is_client_buffer;
-	struct wl_buffer *buffer;
-	struct wl_listener buffer_destroy_listener;
+	struct weston_buffer_reference buffer_ref;
 };
 
 struct drm_output {
@@ -208,10 +207,7 @@ drm_fb_destroy_callback(struct gbm_bo *bo, void *data)
 	if (fb->fb_id)
 		drmModeRmFB(gbm_device_get_fd(gbm), fb->fb_id);
 
-	if (fb->buffer) {
-		weston_buffer_post_release(fb->buffer);
-		wl_list_remove(&fb->buffer_destroy_listener.link);
-	}
+	weston_buffer_reference(&fb->buffer_ref, NULL);
 
 	free(data);
 }
@@ -231,7 +227,7 @@ drm_fb_get_from_bo(struct gbm_bo *bo, struct drm_compositor *compositor)
 
 	fb->bo = bo;
 	fb->is_client_buffer = 0;
-	fb->buffer = NULL;
+	fb->buffer_ref.buffer = NULL;
 
 	width = gbm_bo_get_width(bo);
 	height = gbm_bo_get_height(bo);
@@ -282,27 +278,14 @@ err_free:
 	return NULL;
 }
 
-static void
-fb_handle_buffer_destroy(struct wl_listener *listener, void *data)
-{
-	struct drm_fb *fb = container_of(listener, struct drm_fb,
-					 buffer_destroy_listener);
-
-	fb->buffer = NULL;
-}
-
 static void
 drm_fb_set_buffer(struct drm_fb *fb, struct wl_buffer *buffer)
 {
-	assert(fb->buffer == NULL);
+	assert(fb->buffer_ref.buffer == NULL);
 
 	fb->is_client_buffer = 1;
-	fb->buffer = buffer;
-	fb->buffer->busy_count++;
-	fb->buffer_destroy_listener.notify = fb_handle_buffer_destroy;
 
-	wl_signal_add(&fb->buffer->resource.destroy_signal,
-		      &fb->buffer_destroy_listener);
+	weston_buffer_reference(&fb->buffer_ref, buffer);
 }
 
 static int
@@ -340,19 +323,20 @@ drm_output_prepare_scanout_surface(struct weston_output *_output,
 	struct drm_output *output = (struct drm_output *) _output;
 	struct drm_compositor *c =
 		(struct drm_compositor *) output->base.compositor;
+	struct wl_buffer *buffer = es->buffer_ref.buffer;
 	struct gbm_bo *bo;
 
 	if (es->geometry.x != output->base.x ||
 	    es->geometry.y != output->base.y ||
-	    es->buffer == NULL ||
-	    es->buffer->width != output->base.current->width ||
-	    es->buffer->height != output->base.current->height ||
+	    buffer == NULL ||
+	    buffer->width != output->base.current->width ||
+	    buffer->height != output->base.current->height ||
 	    output->base.transform != es->buffer_transform ||
 	    es->transform.enabled)
 		return NULL;
 
 	bo = gbm_bo_import(c->gbm, GBM_BO_IMPORT_WL_BUFFER,
-			   es->buffer, GBM_BO_USE_SCANOUT);
+			   buffer, GBM_BO_USE_SCANOUT);
 
 	/* Unable to use the buffer for scanout */
 	if (!bo)
@@ -369,7 +353,7 @@ drm_output_prepare_scanout_surface(struct weston_output *_output,
 		return NULL;
 	}
 
-	drm_fb_set_buffer(output->next, es->buffer);
+	drm_fb_set_buffer(output->next, buffer);
 
 	return &output->fb_plane;
 }
@@ -601,13 +585,13 @@ drm_output_prepare_overlay_surface(struct weston_output *output_base,
 	if (es->output_mask != (1u << output_base->id))
 		return NULL;
 
-	if (es->buffer == NULL)
+	if (es->buffer_ref.buffer == NULL)
 		return NULL;
 
 	if (es->alpha != 1.0f)
 		return NULL;
 
-	if (wl_buffer_is_shm(es->buffer))
+	if (wl_buffer_is_shm(es->buffer_ref.buffer))
 		return NULL;
 
 	if (!drm_surface_transform_supported(es))
@@ -628,7 +612,7 @@ drm_output_prepare_overlay_surface(struct weston_output *output_base,
 		return NULL;
 
 	bo = gbm_bo_import(c->gbm, GBM_BO_IMPORT_WL_BUFFER,
-			   es->buffer, GBM_BO_USE_SCANOUT);
+			   es->buffer_ref.buffer, GBM_BO_USE_SCANOUT);
 	if (!bo)
 		return NULL;
 
@@ -645,7 +629,7 @@ drm_output_prepare_overlay_surface(struct weston_output *output_base,
 		return NULL;
 	}
 
-	drm_fb_set_buffer(s->next, es->buffer);
+	drm_fb_set_buffer(s->next, es->buffer_ref.buffer);
 
 	box = pixman_region32_extents(&es->transform.boundingbox);
 	s->plane.x = box->x1;
@@ -715,7 +699,8 @@ drm_output_prepare_cursor_surface(struct weston_output *output_base,
 		return NULL;
 	if (c->cursors_are_broken)
 		return NULL;
-	if (es->buffer == NULL || !wl_buffer_is_shm(es->buffer) ||
+	if (es->buffer_ref.buffer == NULL ||
+	    !wl_buffer_is_shm(es->buffer_ref.buffer) ||
 	    es->geometry.width > 64 || es->geometry.height > 64)
 		return NULL;
 
@@ -742,14 +727,15 @@ drm_output_set_cursor(struct drm_output *output)
 		return;
 	}
 
-	if (es->buffer && pixman_region32_not_empty(&output->cursor_plane.damage)) {
+	if (es->buffer_ref.buffer &&
+	    pixman_region32_not_empty(&output->cursor_plane.damage)) {
 		pixman_region32_fini(&output->cursor_plane.damage);
 		pixman_region32_init(&output->cursor_plane.damage);
 		output->current_cursor ^= 1;
 		bo = output->cursor_bo[output->current_cursor];
 		memset(buf, 0, sizeof buf);
-		stride = wl_shm_buffer_get_stride(es->buffer);
-		s = wl_shm_buffer_get_data(es->buffer);
+		stride = wl_shm_buffer_get_stride(es->buffer_ref.buffer);
+		s = wl_shm_buffer_get_data(es->buffer_ref.buffer);
 		for (i = 0; i < es->geometry.height; i++)
 			memcpy(buf + i * 64, s + i * stride,
 			       es->geometry.width * 4);

src/compositor-rpi.c

@@ -746,7 +746,8 @@ rpi_assign_plane(struct weston_surface *surface, struct rpi_output *output)
 	}
 
 	/* only shm surfaces supported */
-	if (surface->buffer && !wl_buffer_is_shm(surface->buffer)) {
+	if (surface->buffer_ref.buffer &&
+	    !wl_buffer_is_shm(surface->buffer_ref.buffer)) {
 		DBG("surface %p rejected: not shm\n", surface);
 		return NULL;
 	}
@@ -760,7 +761,7 @@ rpi_assign_plane(struct weston_surface *surface, struct rpi_output *output)
 		element->plane.y = floor(surface->geometry.y);
 		DBG("surface %p reuse element %p\n", surface, element);
 	} else {
-		if (!surface->buffer) {
+		if (!surface->buffer_ref.buffer) {
 			DBG("surface %p rejected: no buffer\n", surface);
 			return NULL;
 		}
@@ -817,7 +818,8 @@ rpi_output_assign_planes(struct weston_output *base)
 			 * damage, if the plane is new, so no need to force
 			 * initial resource update.
 			 */
-			if (rpi_element_damage(element, surface->buffer,
+			if (rpi_element_damage(element,
+					       surface->buffer_ref.buffer,
 					       &surface->damage) < 0) {
 				rpi_element_schedule_destroy(element);
 				DBG("surface %p rejected: resource update failed\n",

src/compositor.c

@@ -180,16 +180,6 @@ weston_client_launch(struct weston_compositor *compositor,
 	return client;
 }
 
-static void
-surface_handle_buffer_destroy(struct wl_listener *listener, void *data)
-{
-	struct weston_surface *es =
-		container_of(listener, struct weston_surface, 
-			     buffer_destroy_listener);
-
-	es->buffer = NULL;
-}
-
 static void
 surface_handle_pending_buffer_destroy(struct wl_listener *listener, void *data)
 {
@@ -241,7 +231,6 @@ weston_surface_create(struct weston_compositor *compositor)
 
 	pixman_region32_init(&surface->texture_damage);
 
-	surface->buffer = NULL;
 	surface->buffer_transform = WL_OUTPUT_TRANSFORM_NORMAL;
 	surface->pending.buffer_transform = surface->buffer_transform;
 	surface->output = NULL;
@@ -254,9 +243,6 @@ weston_surface_create(struct weston_compositor *compositor)
 	pixman_region32_init(&surface->transform.opaque);
 	wl_list_init(&surface->frame_callback_list);
 
-	surface->buffer_destroy_listener.notify =
-		surface_handle_buffer_destroy;
-
 	wl_list_init(&surface->geometry.transformation_list);
 	wl_list_insert(&surface->geometry.transformation_list,
 		       &surface->transform.position.link);
@@ -731,9 +717,9 @@ weston_surface_buffer_width(struct weston_surface *surface)
 	case WL_OUTPUT_TRANSFORM_270:
 	case WL_OUTPUT_TRANSFORM_FLIPPED_90:
 	case WL_OUTPUT_TRANSFORM_FLIPPED_270:
-		return surface->buffer->height;
+		return surface->buffer_ref.buffer->height;
 	default:
-		return surface->buffer->width;
+		return surface->buffer_ref.buffer->width;
 	}
 }
 
@@ -745,9 +731,9 @@ weston_surface_buffer_height(struct weston_surface *surface)
 	case WL_OUTPUT_TRANSFORM_270:
 	case WL_OUTPUT_TRANSFORM_FLIPPED_90:
 	case WL_OUTPUT_TRANSFORM_FLIPPED_270:
-		return surface->buffer->width;
+		return surface->buffer_ref.buffer->width;
 	default:
-		return surface->buffer->height;
+		return surface->buffer_ref.buffer->height;
 	}
 }
 
@@ -877,8 +863,7 @@ destroy_surface(struct wl_resource *resource)
 	if (surface->pending.buffer)
 		wl_list_remove(&surface->pending.buffer_destroy_listener.link);
 
-	if (surface->buffer)
-		wl_list_remove(&surface->buffer_destroy_listener.link);
+	weston_buffer_reference(&surface->buffer_ref, NULL);
 
 	pixman_region32_fini(&surface->texture_damage);
 	compositor->renderer->destroy_surface(surface);
@@ -907,26 +892,47 @@ weston_surface_destroy(struct weston_surface *surface)
 }
 
 static void
-weston_surface_attach(struct weston_surface *surface, struct wl_buffer *buffer)
+weston_buffer_reference_handle_destroy(struct wl_listener *listener,
+				       void *data)
+{
+	struct weston_buffer_reference *ref =
+		container_of(listener, struct weston_buffer_reference,
+			     destroy_listener);
+
+	assert((struct wl_buffer *)data == ref->buffer);
+	ref->buffer = NULL;
+}
+
+WL_EXPORT void
+weston_buffer_reference(struct weston_buffer_reference *ref,
+			struct wl_buffer *buffer)
 {
-	if (surface->buffer && buffer != surface->buffer) {
-		weston_buffer_post_release(surface->buffer);
-		wl_list_remove(&surface->buffer_destroy_listener.link);
+	if (ref->buffer && buffer != ref->buffer) {
+		weston_buffer_post_release(ref->buffer);
+		wl_list_remove(&ref->destroy_listener.link);
 	}
 
-	if (buffer && buffer != surface->buffer) {
+	if (buffer && buffer != ref->buffer) {
 		buffer->busy_count++;
 		wl_signal_add(&buffer->resource.destroy_signal,
-			      &surface->buffer_destroy_listener);
+			      &ref->destroy_listener);
 	}
 
+	ref->buffer = buffer;
+	ref->destroy_listener.notify = weston_buffer_reference_handle_destroy;
+}
+
+static void
+weston_surface_attach(struct weston_surface *surface, struct wl_buffer *buffer)
+{
+	weston_buffer_reference(&surface->buffer_ref, buffer);
+
 	if (!buffer) {
 		if (weston_surface_is_mapped(surface))
 			weston_surface_unmap(surface);
 	}
 
 	surface->compositor->renderer->attach(surface, buffer);
-	surface->buffer = buffer;
 }
 
 WL_EXPORT void
@@ -1006,7 +1012,8 @@ static void
 surface_accumulate_damage(struct weston_surface *surface,
 			  pixman_region32_t *opaque)
 {
-	if (surface->buffer && wl_buffer_is_shm(surface->buffer))
+	if (surface->buffer_ref.buffer &&
+	    wl_buffer_is_shm(surface->buffer_ref.buffer))
 		surface->compositor->renderer->flush_damage(surface);
 
 	if (surface->transform.enabled) {
@@ -1243,6 +1250,8 @@ surface_attach(struct wl_client *client,
 	if (buffer_resource)
 		buffer = buffer_resource->data;
 
+	/* Attach, attach, without commit in between does not send
+	 * wl_buffer.release. */
 	if (surface->pending.buffer)
 		wl_list_remove(&surface->pending.buffer_destroy_listener.link);
 
@@ -1380,7 +1389,7 @@ surface_commit(struct wl_client *client, struct wl_resource *resource)
 	if (surface->pending.buffer || surface->pending.remove_contents)
 		weston_surface_attach(surface, surface->pending.buffer);
 
-	if (surface->buffer && surface->configure)
+	if (surface->buffer_ref.buffer && surface->configure)
 		surface->configure(surface, surface->pending.sx,
 				   surface->pending.sy);
 	surface->pending.sx = 0;
@@ -2126,7 +2135,8 @@ pointer_cursor_surface_configure(struct weston_surface *es,
 	y = wl_fixed_to_int(seat->seat.pointer->y) - seat->hotspot_y;
 
 	weston_surface_configure(seat->sprite, x, y,
-				 es->buffer->width, es->buffer->height);
+				 es->buffer_ref.buffer->width,
+				 es->buffer_ref.buffer->height);
 
 	empty_region(&es->pending.input);
 
@@ -2192,7 +2202,7 @@ pointer_set_cursor(struct wl_client *client, struct wl_resource *resource,
 	seat->hotspot_x = x;
 	seat->hotspot_y = y;
 
-	if (surface->buffer)
+	if (surface->buffer_ref.buffer)
 		pointer_cursor_surface_configure(surface, 0, 0);
 }
 
@@ -2567,7 +2577,8 @@ drag_surface_configure(struct weston_surface *es, int32_t sx, int32_t sy)
 
 	weston_surface_configure(es,
 				 es->geometry.x + sx, es->geometry.y + sy,
-				 es->buffer->width, es->buffer->height);
+				 es->buffer_ref.buffer->width,
+				 es->buffer_ref.buffer->height);
 }
 
 static int
@@ -2615,7 +2626,7 @@ device_map_drag_surface(struct weston_seat *seat)
 	struct wl_list *list;
 
 	if (weston_surface_is_mapped(seat->drag_surface) ||
-	    !seat->drag_surface->buffer)
+	    !seat->drag_surface->buffer_ref.buffer)
 		return;
 
 	if (seat->sprite && weston_surface_is_mapped(seat->sprite))

src/compositor.h

@@ -345,6 +345,11 @@ struct weston_compositor {
 	struct weston_xkb_info xkb_info;
 };
 
+struct weston_buffer_reference {
+	struct wl_buffer *buffer;
+	struct wl_listener destroy_listener;
+};
+
 struct weston_region {
 	struct wl_resource resource;
 	pixman_region32_t region;
@@ -437,8 +442,7 @@ struct weston_surface {
 
 	struct wl_list frame_callback_list;
 
-	struct wl_buffer *buffer;
-	struct wl_listener buffer_destroy_listener;
+	struct weston_buffer_reference buffer_ref;
 	uint32_t buffer_transform;
 
 	/* All the pending state, that wl_surface.commit will apply. */
@@ -686,6 +690,10 @@ weston_surface_unmap(struct weston_surface *surface);
 void
 weston_buffer_post_release(struct wl_buffer *buffer);
 
+void
+weston_buffer_reference(struct weston_buffer_reference *ref,
+			struct wl_buffer *buffer);
+
 uint32_t
 weston_compositor_get_time(void);
 

src/gl-renderer.c

@@ -1038,6 +1038,7 @@ gl_renderer_flush_damage(struct weston_surface *surface)
 {
 	struct gl_renderer *gr = get_renderer(surface->compositor);
 	struct gl_surface_state *gs = get_surface_state(surface);
+	struct wl_buffer *buffer = surface->buffer_ref.buffer;
 
 #ifdef GL_UNPACK_ROW_LENGTH
 	pixman_box32_t *rectangles;
@@ -1061,9 +1062,9 @@ gl_renderer_flush_damage(struct weston_surface *surface)
 
 	if (!gr->has_unpack_subimage) {
 		glTexImage2D(GL_TEXTURE_2D, 0, GL_BGRA_EXT,
-			     surface->pitch, surface->buffer->height, 0,
+			     surface->pitch, buffer->height, 0,
 			     GL_BGRA_EXT, GL_UNSIGNED_BYTE,
-			     wl_shm_buffer_get_data(surface->buffer));
+			     wl_shm_buffer_get_data(buffer));
 
 		goto done;
 	}
@@ -1071,7 +1072,7 @@ gl_renderer_flush_damage(struct weston_surface *surface)
 #ifdef GL_UNPACK_ROW_LENGTH
 	/* Mesa does not define GL_EXT_unpack_subimage */
 	glPixelStorei(GL_UNPACK_ROW_LENGTH, surface->pitch);
-	data = wl_shm_buffer_get_data(surface->buffer);
+	data = wl_shm_buffer_get_data(buffer);
 	rectangles = pixman_region32_rectangles(&surface->texture_damage, &n);
 	for (i = 0; i < n; i++) {
 		pixman_box32_t r;

src/shell.c

@@ -1667,7 +1667,7 @@ shell_configure_fullscreen(struct shell_surface *shsurf)
 
 	switch (shsurf->fullscreen.type) {
 	case WL_SHELL_SURFACE_FULLSCREEN_METHOD_DEFAULT:
-		if (surface->buffer)
+		if (surface->buffer_ref.buffer)
 			center_on_output(surface, shsurf->fullscreen_output);
 		break;
 	case WL_SHELL_SURFACE_FULLSCREEN_METHOD_SCALE:

src/tablet-shell.c

@@ -132,8 +132,8 @@ tablet_shell_surface_configure(struct weston_surface *surface,
 	if (weston_surface_is_mapped(surface))
 		return;
 
-	width = surface->buffer->width;
-	height = surface->buffer->height;
+	width = surface->buffer_ref.buffer->width;
+	height = surface->buffer_ref.buffer->height;
 
 	weston_surface_configure(surface, 0, 0, width, height);