Concurrent hash maps.
This crate implements concurrent hash maps, based on bucket-level multi-reader locks. It has excellent performance characteristics¹ and supports resizing, in-place mutation and more.
The API derives directly from std::collections::HashMap, giving it a familiar feel.
¹Note that it heavily depends on the behavior of your program, but in most cases, it's really good. In some (rare) cases you might want atomic hash maps instead.