Map in map syncronization

Question

Hi guys! I'm new to threads so sorry if my question is dumb.
So here it goes: I was wondering if read/writes from something like this: ConcurrentHashMap<String,ConcurrentHashMap<Integer,ConcurrentHashMap<String,Object>>> are thread safe?
ConcurrentHashMap offers thread safety without locking wich is preatty cool but i don't think that combining more of them keeps is right. What do you think?
Thank you!
Cristian

Answer 1

cvrabie wrote:
ConcurrentHashMap offers thread safety without locking wich is preatty cool but i don't think that combining more of them keeps is right. What do you think?
Thank you!
CristianWell, it seems not quite true: there is locking in case of concurrent collection classes, but it is implemented in a different way that the one in case of synchronized collection classes. Here is an excerpt from Brian Goetz "Java Concurrency in Practice " book (section "5.2.1. ConcurrentHashMap"):
"...ConcurrentHashMap is a hash-based Map like HashMap, but it uses an *entirely different locking strategy* that offers better concurrency and scalability. *Instead of synchronizing every method on a common lock*, restricting access to a single thread at a time, *it uses a finer-grained locking mechanism called lock striping* (see Section 11.4.3) to allow a greater degree of shared access..."
And, btw, this is the reason why concurrent collections are not only "don't throw ConcurrentModificationException", but "not even able" to throw them.