[concurrency-interest] Asynchronous-nature of ConcurrentLinkedQueue
gergg at cox.net
Tue May 18 18:28:17 EDT 2010
Doug Lea wrote:
> On 05/18/10 08:03, Kai Meder wrote:
>> reading the Java-Docs of ConcurrentLinkedQueue I wonder what the
>> "asynchronous nature" mentioned in the size()-doc is?
>> "Beware that, unlike in most collections, this method is NOT a
>> constant-time operation. Because of the asynchronous nature of these
>> queues, determining the current number of elements requires an O(n)
>> traversal. "
> Because insertion and removal operations can occur concurrently
> (even while you are asking about the size), you generally
> don't want to ask about the size (although isEmpty is usually
> still useful). But if you do ask, the queue
> will provide an answer by counting up the elements. The
> answer it returns might not have much bearing to the actual
> number of elements upon return of the method.
And I guess I am always curious why there is no "counter" associated with the
queue length. It would provide the same "rough" estimate as the "traversal"
without the repeated overhead would it not?
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