  class Allocator = std::allocator&lt;std::pair&lt;const K, V&gt;&gt;,
          size_t N        = 4,                 // 2**N submaps
          class Mutex     = absl::NullMutex&gt;   // use absl::Mutex to enable internal locks
class parallel_flat_hash_map;
</code></pre>
<p>Let's see what result we get for the insertion of random values from multiple threads, however this time we create a <em>parallel_hash_map</em> with internal locking (by providing absl::Mutex as the last template argument), and modify th