shm: Add shm_buffer ref and shm_pool unref functions

Sometimes the compositor wants to make sure a shm pool doesn't disappear
out from under it.

For example, in Enlightenment, rendering happens in a separate thread
while the main thread can still dispatch events.  If a client is destroyed
during rendering, all its resources are cleaned up and its shm pools are
unmapped.  This causes the rendering thread to segfault.

This patch adds a way for the compositor to increment the refcount of the
shm pool so it can't disappear, and decrement it when it's finished.

The ref/unref are asymmetrical (ref returns the pool) because it's
possible the buffer itself will be gone when you need to unref the pool.

Reviewed-by: Pekka Paalanen <pekka.paalanen@collabora.co.uk>
Signed-off-by: Derek Foreman <derekf@osg.samsung.com>

1 files changed, 7 insertions, 0 deletions

diff --git a/src/wayland-server-core.h b/src/wayland-server-core.h
index e605432..4c2bdfe 100644
--- a/src/wayland-server-core.h
+++ b/src/wayland-server-core.h
@@ -362,6 +362,7 @@ wl_resource_get_destroy_listener(struct wl_resource *resource,
 	     resource = tmp,							\
 	     tmp = wl_resource_from_link(wl_resource_get_link(resource)->next))
 
+struct wl_shm_pool;
 struct wl_shm_buffer;
 
 void
@@ -388,6 +389,12 @@ wl_shm_buffer_get_width(struct wl_shm_buffer *buffer);
 int32_t
 wl_shm_buffer_get_height(struct wl_shm_buffer *buffer);
 
+struct wl_shm_pool *
+wl_shm_buffer_ref_pool(struct wl_shm_buffer *buffer);
+
+void
+wl_shm_pool_unref(struct wl_shm_pool *pool);
+
 int
 wl_display_init_shm(struct wl_display *display);