Re: Data structure to keep things in memory

Without going into all the details, I have the following situation:

There are a set of objects RTS, all of the same type, that gather
run-time statistics about the running of a program. Various related
objects with different lifecycles pass them around and use them. I'm
interested in when each member of RTS is no longer being updated,
because I want to collect its final statistics , but there's no good way
to tell when it's no longer in use except via its collection, so when
it's created I attach a weak reference to it and associate the weak
reference with a queue. When the reference is delivered, I record the
statistics. [1]

So far so good. The question is, what's the best way to keep the
references in memory until they can be delivered to the queue?
Obviously, I could put them into a synchronized HashSet, but I'd prefer
to optimize for concurrency by minimizing locking. At the moment, I'm
using a ConcurrentHashMap, since it seems to give the best concurrency
for updates. (The usage pattern is a bit unusual, since there are
effectively no lookups. There's a put() when the reference is created,
and a remove() when it's pulled out of the reference queue.) This is an
area where I have very little experience, so I'd welcome input from
anyone who's worked with these classes.

1. Obviously, a member of RTS points to a separate statistics object
which is also pointed to by the weak reference.