l::NullMutex</code>, which does no locking and has no size cost). When selecting <code>absl::Mutex</code>, one mutex is created for each internal submap at a cost of 8 bytes per submap, and the <em>parallel_hash_map</em> internally protects each submap access with its associated mutex.</p>
<table>
<thead>
<tr class="header">
<th style="text-align: left;">map</th>
<th style="text-align: center;">Number of submaps</th>
<th style="text-align: right;">sizeof(map)</th>
</tr>
</thead>
<tbody>
<tr class="odd">
<td