[concurrency-interest] Frequently canceled timers

Doug Lea dl at cs.oswego.edu
Fri Jan 25 13:52:06 EST 2008

Richard Johns wrote:
> I have an application that retransmits messages when they don't get a 
> timely response .  Usually, of course, that's not necessary and their 
> timers are canceled.  This is a traffic generator so message rate is 
> high and we need to remove the canceled timers.
> Is there a timer implementation that efficiently cleans up canceled 
> timers?  DelayQueue uses a binary heap so it's very fast otherwise, but 
> it uses a sequential search for remove().  ScheduledThreadPoolExecutor 
> uses DelayQueue, and Timer also uses a binary heap.

Sorry for not paying attention to this before others replied...

Last september, we put out revised version of ScheduledThreadPoolExecutor
that uses an internal variant of DelayQueue that includes fast eager
cleanup on cancel. This isn't scheduled to get out until Java7 though.
Which looks like it might be a while.
And even then. because of compatibility concerns, fast cleanup won't
be default enabled -- see method setRemoveOnCancelPolicy(boolean).
(Although hopefully this will be reconsidered later.)

But until then you may be able to use or adapt our version in
CVS, that relies also on updated version of ThreadPoolExecutor
that you can also get from CVS.



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