# Chapter 9
Timers, Hash Map, Union-find, Modifiers

Lutz Kettner, Matthias Bäsken, Sylvain Pion, and Micheal Seel

## Summary

This chapter decribes classes for measuring user process time and real time as well as the memory size.

A hash map CGAL::Unique_hash_map is offered that is specialized on unique hash values of type std::size_t, i.e., it is particularly useful for pointers, handles, iterators, and circulators as key values.

Furthermore, a union-find data structure and the modifier base class is documented.

### Concepts

UniqueHashFunction

### Classes

CGAL::Timer
CGAL::Real_timer
CGAL::Memory_sizer

CGAL::Unique_hash_map<Key,Data,UniqueHashFunction>
CGAL::Handle_hash_function

CGAL::Union_find<T,A>

CGAL::Modifier_base<R>

## Reference Pages

- Handle_hash_function

- Memory_sizer

- Modifier_base<R>

- Real_timer

- Timer

- Union_find<T,A>

- Unique_hash_map<Key,Data,UniqueHashFunction>

- UniqueHashFunction