title: Super high performance C/C++ hash map (table, dictionary)
body: <p>I need to map primitive keys (int, maybe long) to struct values in a high-performance hash map data structure.</p>
  
  <p>My program will have a few hundred of these maps, and each map will generally have at most a few thousand entries. However, the maps will be "refreshing" or "churning" constantly; imagine processing millions of <code>add</code> and <code>delete</code> messages a second.</p>
  
  <p>What libraries in C or C++ have a data structure that fits this use case? Or, how would you recommend building your own? Thanks!</p>