 the finer grained locking of the <em>parallel_hash_map</em> (separate locks for each internal submap) will provide a speed benefit when compared to the single threaded insertion, and this is indeed what the benchmarks show:</p>
<p><img src="https://github.com/greg7mdp/parallel-hashmap/blob/master/img/flat_par_mutex_4.PNG?raw=true" alt="flat_par_mutex_4" /></p>
<p>Interestingly, we notice that the memory peaks (when resizing occur) are again very small, in the order of 1/16th of those for the <em>flat_hash_