In a concurrent environment, I wonder if the overhead of wrapping every API call with a synchronized would make this significantly slower than using ConcurrentHashMap.
If we just wrap every API call with synchronized, I'd expect heavy contention (some adaptive spinning and then OS-level park/unpark), so it'll likely bottleneck pretty quickly.
Doing something closer to ConcurrentHashMap (locking per bin rather than globally) could mitigate that.
For the open-addressing table itself, I'm also considering adding lightweight locking at the group level (e.g., a small spinlock per group) so reads stay cheap and writes only lock a narrow region along the probe path.