Does a thread put a new value in its own segment in ConcurrentHashMap

Question

I have a ConcurrentHashMap and i try to put a key value pair using putIfAbsent(). Now since each thread working on a concurrentHashMap has its own segment which consists of a set of key value pairs . Will a new key value pair be placed in it own segment or there is nothing mandatory like this ?

Thanks

Answer 1

You have a fundamental misunderstanding. Threads do not have their own segment. The mappings of a ConcurrentHashMap are distributed over the segments depending on the hash codes of their keys and in the best case , threads accessing different keys end up at different segments and hence, may work independently.

Threads accessing the same key can never end up at different segments. The principle of a Map that all keys are unique doesn't change.

But this is a description of an outdated technology anyway. Since Java 8, ConcurrentHashMap does not use segments anymore. Depending on the capacity and the hash code distribution, all keys may get updated concurrently.