Show HN: A concurrent thread-safe hash map implemented in C++

I feel that using a linked list as the underlying structure combined with fine grained locking is the wrong direction to go. What is the scenario in which I would use this collection over an unordered_map and some locking scheme? A linked list is a very (very very) poor performer and I would only use a linked list for implementing a collection which is synchronized based on CAS operations instead of locking. Since your implementation relies on linked lists and fine grained locking, I have a hard time imagining a scenario where I would gain utility. I would start by wrapping the std unordered_map and shared_mutex, testing and measuring the performance as a baseline and only then creating an alternative which could compete. If you want to make it interesting, at least make the synchronization lock free and gain some advantage from using a linked list.

A few issues with this implementation:

Is it really nessecary to allocate all of the hash buckets up front? Why not initialize them to null and then allocate them as you need?

Why not use some kind of managed container like std vector to store the hash buckets? This removes the need to do explicit memory management.

Why not use std forward_list instead of rolling your own linked list? Again, this will reduce the amount of code and save you from having to do manual memory management

Curious if there are any tests.

this doesnt work for collisions