What is the closest to ConcurrentHashMap and NavigableMap in Java?

[Dmitry Olshansky]

15-Nov-2013 03:35, Charles Hixson пишет:
> On 11/14/2013 01:36 PM, ilya-stromberg wrote:
>> On Thursday, 14 November 2013 at 21:31:52 UTC, Jacek Furmankiewicz wrote:
>>> hashmap per thread is not an option. The cache may be a few GBs of
>>> data, there is no way we can duplicate that data per thread.
>>>
>>> Not to mention the start up time when we have to warm up the cache.
>>
>> How often do you change the data? Probably, you should use `immutable`
>> variables.
>>
> Immutable variables are nice when they can be used.  Often, however,
> they can't.
>
> I think that for the "concurrent hashmap" the best answer is probably to
> run the map in a thread, with message passing access whether for read or
> write.

Would be slow unless batched. At least in D message passing involves 
locking/unlocking a queue of messages. Sending back and forth you get 2 
lock-wait-unlock and correspondingly context switches.

> And I wouldn't be surprised if that's how Java's concurrent
> hashmap is implemented under the covers. (OTOH, I haven't ever debugged
> such a setup.  Someone who has may have a better answer.)

As stated in Oracle's documentation somewhere it's implemented with fine 
grained locking (a lock per bucket of a hash map), some operations still 
lock the whole map. Rehashing still locks the whole thing I bet.

-- 
Dmitry Olshansky