radix_tree: warn about using reverse iterator in concurrent env

Author: igchor

include/libpmemobj++/experimental/radix_tree.hpp

@@ -2694,6 +2694,8 @@ radix_tree<Key, Value, BytesView, MtMode>::end() const
 /**
  * Returns a reverse iterator to the beginning.
  *
+ * Using reverse iterators in concurrent environment is not safe.
+ *
  * @return reverse_iterator pointing to the last element in the vector.
  */
 template <typename Key, typename Value, typename BytesView, bool MtMode>
@@ -2706,6 +2708,8 @@ radix_tree<Key, Value, BytesView, MtMode>::rbegin()
 /**
  * Returns a reverse iterator to the end.
  *
+ * Using reverse iterators in concurrent environment is not safe.
+ *
  * @return reverse_iterator pointing to the theoretical element preceding the
  * first element in the vector.
  */
@@ -2719,6 +2723,8 @@ radix_tree<Key, Value, BytesView, MtMode>::rend()
 /**
  * Returns a const, reverse iterator to the beginning.
  *
+ * Using reverse iterators in concurrent environment is not safe.
+ *
  * @return const_reverse_iterator pointing to the last element in the vector.
  */
 template <typename Key, typename Value, typename BytesView, bool MtMode>
@@ -2731,6 +2737,8 @@ radix_tree<Key, Value, BytesView, MtMode>::crbegin() const
 /**
  * Returns a const, reverse iterator to the end.
  *
+ * Using reverse iterators in concurrent environment is not safe.
+ *
  * @return const_reverse_iterator pointing to the theoretical element preceding
  * the first element in the vector.
  */