/**
The item counting is an important part of \p MichaelHashSet algorithm:
the \p empty() member function depends on correct item counting.
- Therefore, \p atomicity::empty_item_counter is not allowed as a type of the option.
+ You may use \p atomicity::empty_item_counter if don't need \p empty() and \p size()
+ member functions.
- Default is \p atomicity::item_counter.
+ Default is \p atomicity::item_counter; to avoid false sharing you may use \p atomicity::cache_friendly_item_counter
*/
typedef cds::atomicity::item_counter item_counter;