[Mesa-dev] [PATCH 1/3] gallium: clarify the constraints on sampler_view_destroy

[Nicolai Hähnle]

From: Nicolai Hähnle <nicolai.haehnle at amd.com>

r600 expects the context that created the sampler view to still be alive
(there is a per-context list of sampler views).

svga currently bails when the context of destruction is not the same as
creation.

The GL state tracker, which is the only one that runs into the
multi-context subtleties (due to share groups), already guarantees that
sampler views are destroyed before their context of creation is destroyed.

Most drivers are context-agnostic, so the warning message in
pipe_sampler_view_release doesn't really make sense.
---
 src/gallium/auxiliary/util/u_inlines.h   | 16 ++++++++++------
 src/gallium/include/pipe/p_context.h     | 10 ++++++++++
 src/mesa/state_tracker/st_sampler_view.c |  1 -
 3 files changed, 20 insertions(+), 7 deletions(-)

diff --git a/src/gallium/auxiliary/util/u_inlines.h b/src/gallium/auxiliary/util/u_inlines.h
index 79f62c32266..790352d7800 100644
--- a/src/gallium/auxiliary/util/u_inlines.h
+++ b/src/gallium/auxiliary/util/u_inlines.h
@@ -142,45 +142,49 @@ pipe_resource_reference(struct pipe_resource **ptr, struct pipe_resource *tex)
          struct pipe_resource *next = old_tex->next;
 
          old_tex->screen->resource_destroy(old_tex->screen, old_tex);
          old_tex = next;
       } while (pipe_reference_described(&old_tex->reference, NULL,
                                         (debug_reference_descriptor)debug_describe_resource));
    }
    *ptr = tex;
 }
 
+/**
+ * Set *ptr to \p view with proper reference counting.
+ *
+ * The caller must guarantee that \p view and *ptr must have been created in
+ * the same context (if they exist), and that this must be the current context.
+ */
 static inline void
 pipe_sampler_view_reference(struct pipe_sampler_view **ptr, struct pipe_sampler_view *view)
 {
    struct pipe_sampler_view *old_view = *ptr;
 
    if (pipe_reference_described(&(*ptr)->reference, &view->reference,
                                 (debug_reference_descriptor)debug_describe_sampler_view))
       old_view->context->sampler_view_destroy(old_view->context, old_view);
    *ptr = view;
 }
 
 /**
  * Similar to pipe_sampler_view_reference() but always set the pointer to
- * NULL and pass in an explicit context.  Passing an explicit context is a
- * work-around for fixing a dangling context pointer problem when textures
- * are shared by multiple contexts.  XXX fix this someday.
+ * NULL and pass in the current context explicitly.
+ *
+ * If *ptr is non-NULL, it may refer to a view that was created in a different
+ * context (however, that context must still be alive).
  */
 static inline void
 pipe_sampler_view_release(struct pipe_context *ctx,
                           struct pipe_sampler_view **ptr)
 {
    struct pipe_sampler_view *old_view = *ptr;
-   if (*ptr && (*ptr)->context != ctx) {
-      debug_printf_once(("context mis-match in pipe_sampler_view_release()\n"));
-   }
    if (pipe_reference_described(&(*ptr)->reference, NULL,
                     (debug_reference_descriptor)debug_describe_sampler_view)) {
       ctx->sampler_view_destroy(ctx, old_view);
    }
    *ptr = NULL;
 }
 
 static inline void
 pipe_so_target_reference(struct pipe_stream_output_target **ptr,
                          struct pipe_stream_output_target *target)
diff --git a/src/gallium/include/pipe/p_context.h b/src/gallium/include/pipe/p_context.h
index 4609d4dbf23..087836d1c0c 100644
--- a/src/gallium/include/pipe/p_context.h
+++ b/src/gallium/include/pipe/p_context.h
@@ -501,20 +501,30 @@ struct pipe_context {
    void (*fence_server_sync)(struct pipe_context *pipe,
                              struct pipe_fence_handle *fence);
 
    /**
     * Create a view on a texture to be used by a shader stage.
     */
    struct pipe_sampler_view * (*create_sampler_view)(struct pipe_context *ctx,
                                                      struct pipe_resource *texture,
                                                      const struct pipe_sampler_view *templat);
 
+   /**
+    * Destroy a view on a texture.
+    *
+    * \param ctx the current context
+    * \param view the view to be destroyed
+    *
+    * \note The current context may not be the context in which the view was
+    *       created (view->context). However, the caller must guarantee that
+    *       the context which created the view is still alive.
+    */
    void (*sampler_view_destroy)(struct pipe_context *ctx,
                                 struct pipe_sampler_view *view);
 
 
    /**
     * Get a surface which is a "view" into a resource, used by
     * render target / depth stencil stages.
     */
    struct pipe_surface *(*create_surface)(struct pipe_context *ctx,
                                           struct pipe_resource *resource,
diff --git a/src/mesa/state_tracker/st_sampler_view.c b/src/mesa/state_tracker/st_sampler_view.c
index 0d7b63af75a..892725671d2 100644
--- a/src/mesa/state_tracker/st_sampler_view.c
+++ b/src/mesa/state_tracker/st_sampler_view.c
@@ -109,21 +109,20 @@ st_texture_release_sampler_view(struct st_context *st,
 /**
  * Release all sampler views attached to the given texture object, regardless
  * of the context.
  */
 void
 st_texture_release_all_sampler_views(struct st_context *st,
                                      struct st_texture_object *stObj)
 {
    GLuint i;
 
-   /* XXX This should use sampler_views[i]->pipe, not st->pipe */
    for (i = 0; i < stObj->num_sampler_views; ++i)
       pipe_sampler_view_release(st->pipe, &stObj->sampler_views[i].view);
 }
 
 
 void
 st_texture_free_sampler_views(struct st_texture_object *stObj)
 {
    free(stObj->sampler_views);
    stObj->sampler_views = NULL;
-- 
2.11.0