Re:Building an efficient hash table in Java
by bluuewhale on Monday December 15, 2025 @08:36PM
(#46283643)
Thanks. This is actually one of the topics I really want to tackle next.
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.
Re:Building an efficient hash table in Java
by poorman on Monday December 15, 2025 @09:04PM
(#46283845)
I think that's a great idea! I just checked one of my larger projects and it 55% ConcurrentHashMap and 45% HashMap so I'd personally benefit from this plan.
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.