[Runtime][Object] Add Object::unique() (apache#7615)

include/tvm/runtime/object.h

@@ -185,7 +185,11 @@ class TVM_DLL Object {
    */
   template <typename TargetType>
   inline bool IsInstance() const;
-
+  /*!
+   * \return Weather the cell has only one reference
+   * \note We use stl style naming to be consistent with known API in shared_ptr.
+   */
+  inline bool unique() const;
   /*!
    * \brief Get the type key of the corresponding index from runtime.
    * \param tindex The type index.
@@ -831,6 +835,8 @@ inline bool Object::IsInstance() const {
   }
 }
 
+inline bool Object::unique() const { return use_count() == 1; }
+
 template <typename ObjectType>
 inline const ObjectType* ObjectRef::as() const {
   if (data_ != nullptr && data_->IsInstance<ObjectType>()) {