[PATCH weston 2/8] compositor: add and export weston_buffer_reference()

[Pekka Paalanen]

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(wl_buffer **ref, wl_buffer *buffer, listener)

Buffer is assigned to *ref, 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. Registering and
de-registering the destroy listener is included.

This is inspired by the pipe_resource_reference() of Mesa.

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

Signed-off-by: Pekka Paalanen <ppaalanen at gmail.com>
---
 src/compositor.c |   31 +++++++++++++++++++++----------
 src/compositor.h |    4 ++++
 2 files changed, 25 insertions(+), 10 deletions(-)

diff --git a/src/compositor.c b/src/compositor.c
index 3399ad4..c1fc287 100644
--- a/src/compositor.c
+++ b/src/compositor.c
@@ -779,8 +779,8 @@ 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, NULL,
+				&surface->buffer_destroy_listener);
 
 	pixman_region32_fini(&surface->texture_damage);
 	compositor->renderer->destroy_surface(surface);
@@ -808,27 +808,36 @@ weston_surface_destroy(struct weston_surface *surface)
 	destroy_surface(&surface->surface.resource);
 }
 
-static void
-weston_surface_attach(struct weston_surface *surface, struct wl_buffer *buffer)
+WL_EXPORT void
+weston_buffer_reference(struct wl_buffer **ref, struct wl_buffer *buffer,
+			struct wl_listener *buffer_destroy_listener)
 {
-	if (surface->buffer && buffer != surface->buffer) {
-		weston_buffer_post_release(surface->buffer);
-		wl_list_remove(&surface->buffer_destroy_listener.link);
+	if (*ref && buffer != *ref) {
+		weston_buffer_post_release(*ref);
+		wl_list_remove(&buffer_destroy_listener->link);
 	}
 
-	if (buffer && buffer != surface->buffer) {
+	if (buffer && buffer != *ref) {
 		buffer->busy_count++;
 		wl_signal_add(&buffer->resource.destroy_signal,
-			      &surface->buffer_destroy_listener);
+			      buffer_destroy_listener);
 	}
 
+	*ref = buffer;
+}
+
+static void
+weston_surface_attach(struct weston_surface *surface, struct wl_buffer *buffer)
+{
+	weston_buffer_reference(&surface->buffer, buffer,
+				&surface->buffer_destroy_listener);
+
 	if (!buffer) {
 		if (weston_surface_is_mapped(surface))
 			weston_surface_unmap(surface);
 	}
 
 	surface->compositor->renderer->attach(surface, buffer);
-	surface->buffer = buffer;
 }
 
 WL_EXPORT void
@@ -1147,6 +1156,8 @@ 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);
 
diff --git a/src/compositor.h b/src/compositor.h
index e770664..9809238 100644
--- a/src/compositor.h
+++ b/src/compositor.h
@@ -669,6 +669,10 @@ weston_surface_unmap(struct weston_surface *surface);
 void
 weston_buffer_post_release(struct wl_buffer *buffer);
 
+void
+weston_buffer_reference(struct wl_buffer **ref, struct wl_buffer *buffer,
+			struct wl_listener *buffer_destroy_listener);
+
 uint32_t
 weston_compositor_get_time(void);
 
-- 
1.7.8.6