source/blender/blenkernel/BKE_anonymous_attribute_id.hh

@@ -54,7 +54,7 @@ class AnonymousAttributeID : public ImplicitSharingMixin {
 };
 
 /** Wrapper for #AnonymousAttributeID that avoids manual reference counting. */
-using AutoAnonymousAttributeID = ImplicitSharePtr<const AnonymousAttributeID>;
+using AutoAnonymousAttributeID = ImplicitSharingPtr<const AnonymousAttributeID>;
 
 /**
  * A set of anonymous attribute names that is passed around in geometry nodes.

source/blender/blenkernel/BKE_geometry_set.hh

@@ -101,7 +101,7 @@ inline constexpr bool is_geometry_component_v = std::is_base_of_v<GeometryCompon
  */
 struct GeometrySet {
  private:
-  using GeometryComponentPtr = blender::ImplicitSharePtr<class GeometryComponent>;
+  using GeometryComponentPtr = blender::ImplicitSharingPtr<class GeometryComponent>;
   /* Indexed by #GeometryComponentType. */
   std::array<GeometryComponentPtr, GEO_COMPONENT_TYPE_ENUM_SIZE> components_;
 

source/blender/blenlib/BLI_implicit_sharing.hh

@@ -15,26 +15,27 @@
 namespace blender {
 
 /**
- * #bCopyOnWrite allows implementing copy-on-write behavior, i.e. it allows sharing read-only data
+ * #ImplicitSharingInfo is the core data structure for implicit sharing in Blender. Implicit
- * between multiple independend systems (e.g. meshes). The data is only copied when it is shared
+ * sharing is a technique that avoids copying data when it is not necessary. This results in better
- * and is about to be modified. This is in contrast to making copies before it is actually known
+ * memory usage and performance. Only read-only data can be shared, because otherwise multiple
- * that it is necessary.
+ * owners might want to change the data in conflicting ways.
  *
- * Internally, this is mostly just a glorified reference count. If the reference count is 1, the
+ * To determine whether data is shared, #ImplicitSharingInfo keeps a user count. If the count is 1,
- * data only has a single owner and is mutable. If it is larger than 1, it is shared and must be
+ * the data only has a single owner and is therefore mutable. If some code wants to modify data
- * logically const.
+ * that is currently shared, it has to make a copy first.
+ * This behavior is also called "copy on write".
  *
- * On top of containing a reference count, #bCopyOnWrite also knows how to destruct the referenced
+ * On top of containing a reference count, #ImplicitSharingInfo also knows how to destruct the
- * data. This is important because the code freeing the data in the end might not know how it was
+ * referenced data. This is important because the code freeing the data in the end might not know
- * allocated (for example, it doesn't know whether an array was allocated using the system or
+ * how it was allocated (for example, it doesn't know whether an array was allocated using the
- * guarded allocator).
+ * system or guarded allocator).
  *
- * #bCopyOnWrite is used in two ways:
+ * #ImplicitSharingInfo can be used in two ways:
- * - It can be allocated separately from the referenced data as is typically the case with raw
+ * - It can be allocated separately from the referenced data. This is used when the shared data is
- *   arrays (e.g. for mesh attributes).
+ *   e.g. a plain data array.
  * - It can be embedded into another struct. For that it's best to use #ImplicitSharingMixin.
  */
-struct ImplicitSharingInfo : blender::NonCopyable, blender::NonMovable {
+class ImplicitSharingInfo : blender::NonCopyable, blender::NonMovable {
  private:
   mutable std::atomic<int> users_;
 
@@ -74,14 +75,14 @@ struct ImplicitSharingInfo : blender::NonCopyable, blender::NonMovable {
   }
 
  private:
-  /** Has to free the #bCopyOnWrite and the referenced data. */
+  /** Has to free the #ImplicitSharingInfo and the referenced data. */
   virtual void delete_self_with_data() = 0;
 };
 
 /**
- * Makes it easy to embed copy-on-write behavior into a struct.
+ * Makes it easy to embed implicit-sharing behavior into a struct.
  */
-struct ImplicitSharingMixin : public ImplicitSharingInfo {
+class ImplicitSharingMixin : public ImplicitSharingInfo {
  public:
   ImplicitSharingMixin() : ImplicitSharingInfo(1)
   {

source/blender/blenlib/BLI_implicit_sharing_ptr.hh

@@ -10,33 +10,38 @@
 
 namespace blender {
 
-template<typename T> class ImplicitSharePtr {
+/**
+ * #ImplicitSharingPtr is a smart pointer that manages implicit sharing. It's designed to work with
+ * types that derive from #ImplicitSharingMixin. It is fairly similar to #std::shared_ptr but
+ * expects the reference count to be embedded in the data.
+ */
+template<typename T> class ImplicitSharingPtr {
  private:
   T *data_ = nullptr;
 
  public:
-  ImplicitSharePtr() = default;
+  ImplicitSharingPtr() = default;
 
-  ImplicitSharePtr(T *data) : data_(data)
+  ImplicitSharingPtr(T *data) : data_(data)
   {
   }
 
-  ImplicitSharePtr(const ImplicitSharePtr &other) : data_(other.data_)
+  ImplicitSharingPtr(const ImplicitSharingPtr &other) : data_(other.data_)
   {
     this->add_user(data_);
   }
 
-  ImplicitSharePtr(ImplicitSharePtr &&other) : data_(other.data_)
+  ImplicitSharingPtr(ImplicitSharingPtr &&other) : data_(other.data_)
   {
     other.data_ = nullptr;
   }
 
-  ~ImplicitSharePtr()
+  ~ImplicitSharingPtr()
   {
     this->remove_user_and_delete_if_last(data_);
   }
 
-  ImplicitSharePtr &operator=(const ImplicitSharePtr &other)
+  ImplicitSharingPtr &operator=(const ImplicitSharingPtr &other)
   {
     if (this == &other) {
       return *this;
@@ -48,7 +53,7 @@ template<typename T> class ImplicitSharePtr {
     return *this;
   }
 
-  ImplicitSharePtr &operator=(ImplicitSharePtr &&other)
+  ImplicitSharingPtr &operator=(ImplicitSharingPtr &&other)
   {
     if (this == &other) {
       return *this;
@@ -122,7 +127,7 @@ template<typename T> class ImplicitSharePtr {
     return get_default_hash(data_);
   }
 
-  friend bool operator==(const ImplicitSharePtr &a, const ImplicitSharePtr &b)
+  friend bool operator==(const ImplicitSharingPtr &a, const ImplicitSharingPtr &b)
   {
     return a.data_ == b.data_;
   }

source/blender/geometry/intern/realize_instances.cc

@@ -226,8 +226,8 @@ struct GatherTasks {
 
   /* Volumes only have very simple support currently. Only the first found volume is put into the
    * output. */
-  ImplicitSharePtr<const VolumeComponent> first_volume;
+  ImplicitSharingPtr<const VolumeComponent> first_volume;
-  ImplicitSharePtr<const GeometryComponentEditData> first_edit_data;
+  ImplicitSharingPtr<const GeometryComponentEditData> first_edit_data;
 };
 
 /** Current offsets while during the gather operation. */