xo-gc stack: refactor + streamline.

Retiring unused Collector typealiases.
Fix #include topology.
Fix/improve write barrier setup.

include/xo/gc/DX1Collector.hpp

@@ -307,7 +307,9 @@ namespace xo {
 
             // ----- mutation -----
 
-            /** Modify a gc-owned pointer @p *p_lhs, within allocation @p parent,
+            /** DEPRECATED. Prefer .barrier_assign_aux().
+             *
+             *  Modify a gc-owned pointer @p *p_lhs, within allocation @p parent,
              *  to point to @p rhs.
              *
              *  Motivation: need special handling for cross-generational pointers with

include/xo/gc/MutationLogStore.hpp

@@ -55,14 +55,22 @@ namespace xo {
             void verify_ok() noexcept;
 
             /** on behalf of gc-aware object store @p gc,
-             *  change the value of a child pointer at @p p_lhs
-             *  with parent object @p parent.  p_lhs and parent must belong
-             *  to the same allocation.
+             *  change the value of a child pointer {@p lhs_iface, @p *lhs_data}
+             *  with parent object @p parent, to point to {@p rhs_iface, @p rhs_data}
+             *  p_lhs and parent must belong to the same allocation.
+             *
+             *  @p lhs_iface can be nullptr, if parent holds ordinary pointer
+             *  instead of fop (i.e. DRepr* instead of obj<AFacet,DRepr>).
+             *
+             *  @p rhs_iface must be non-null, it's load-bearing for mlog entry
+             *  snapshot member.
              **/
-            void assign_member(GCObjectStore * gc,
-                               void * parent,
-                               obj<AGCObject> * p_lhs,
-                               obj<AGCObject> rhs);
+            void assign_member_aux(GCObjectStore * gc,
+                                   void * parent,
+                                   AGCObject * lhs_iface,
+                                   void ** lhs_data,
+                                   AGCObject * rhs_iface,
+                                   void * rhs_data);
 
             /** swap {to, from} roles
              **/

include/xo/gc/detail/ICollector_DX1Collector.hpp

@@ -104,6 +104,7 @@ Return false if installation fails (e.g. memory exhausted) **/
  **/
             static void request_gc(DX1Collector & self, Generation upto);
             /** Assign pointer @p p_lhs to destination @p rhs, within parent allocation @p parent
+DEPRECATED. Only used in MockCollector for gc unit test
 
 Require: gc not in progress **/
             static void assign_member(DX1Collector & self, void * parent, obj<AGCObject> * p_lhs, obj<AGCObject> & rhs);