[concurrency-interest] Looking for a data struture

Joe Bowbeer joe.bowbeer at gmail.com
Mon Dec 22 13:05:38 EST 2014


On Sunday, December 21, 2014, Luke Sandberg <lukeisandberg at gmail.com> wrote:

> I have come across a few situations where i am looking for a datastructure
> and i feel like i keep coming up short.
> The situation is analogous to the 'waiters' list in
> java.util.concurrent.FutureTask.
> Basically, I need to be able to publish a non-null object reference into a
> data structure where
> * order doesn't matter (insertion order would be nice, but i don't care
> that much)
> * add and remove identity semantics
> * concurrent iteration (weakly consistent is fine)
> * add/remove are non-blocking
> CLQ is an obvious choice but removal is O(n), another choice would a
> simple synchronized identity hash set which is fine but the lock + high
> entry overhead is a deal breaker.
> An AtomicReferenceArray would be super easy, but i can't put a bound on
> the number of items.
> Also, it would be fine for the code that adds items, to store additional
> state (an index, a 'Node' reference), in order to facilitate removal.
> The best thing i have seen from looking around appears to be something
> like what FutureTask does to implement 'awaitDone', but even there
> removeWaitier() is O(n).  that seems like a pretty good compromise when
> lists are short, but what would be a better solution when lists are long?
> Just to motivate this a little bit, the two cases I am looking at in
> particular are:
> * maintaining a set of threads associated with a server 'request' (threads
> enter/exit when they start executing tasks associated with the request)
> * maintaining a set of futures to be cancelled (futures are removed when
> they complete to avoid pinning their referents).
> Any pointers or ideas?
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