[concurrency-interest] Locking a ConcurrentHashSet in a ConcurrentHasHMap

Tom Hawtin Thomas.Hawtin at Sun.COM
Thu Aug 7 09:57:27 EDT 2008

Mike Bean wrote:
> I was wondering if anyone had some thoughts on how to avoid a lock to 
> allow removal of a ConcurrentHashSet from a ConcurrentHashMap.  Context 
> is an index manager with these two calls:

I guess you could use a doNotUse flag in a subclass of 
ConcurrentHashSet. Set the flag before removing the set. Check the flag 
after adding to it.

If only we had a standard full set of multiset collections and the like...

> I'm also concerned at the memory cost of a ConcurrentHashSet for a 
> single reference to an Entry object but the indexing and unindexing 
> entries gets more complex with the map containing an Entry or a 
> ConcurrentHashSet of Entries.

Are you sure you are going to have significant contention given the map? 
Perhaps a plain set with synchronisation would do. Or an immutable [by 
convention] set.


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