> I wasn't at all clear why changing the frequency (to "never") of message > expiration checks would affect the performance of destination GC operations > when the number of queues is large. Is that due to synchronization between > those two operations, or thread contention because one or both takes longer > than its periodicity to complete so we eventually have more pending threads > than the cores can run, or...
You could look at the imp of purge() on a Timer. It cause the entire queue to be rebuild and heapified again which is slow. Far far slower than synchronized. The synchronized blocks aren’t even really showing up in my timings so I’m not really worried about them. In fact removing them could introduce other issues so I”m hesitant to remove them without actual bugs. > I'm in favor of the changes as you've > described it (I can't think of a reason we'd want advisory messages to > expire, though ideally it would be configurable for just in case someone > has a need for it that I can't think of; configurable or not, having 0 as > the default sounds like a clear win to me), I'm just not clear on how it > has the larger effects you describe. > > We can go either route now. My patches just refactored the way we remove task. Now what I do is I just use an AtomicReference and I can clear() it when I want to remove the timer. The underlying timer will get executed, but since it checks first that it’s non-null it,s just a quick noop once it’s cleared. > Also, can you point me to the O(N^2) code related to Timer.purge()? If it > really is purging every queue each time any queue's timer fires, that > sounds like incorrect code, but I'd like to see it to make sure I'm not > misunderstanding what you're describing. > I’m pretty sure it’s O(N^2)… what’s happening is that for each queue that needs to be GCd, it’s causing a purge. So if you have 1000 queues, it has to purge and rebuild it… then if you have 999 queues, and you remove one, it has to do a full purge and rebuild each time. Now I just have it essentially flag the timer task as clear and it will go through the timer queue and not get executed. If you’re still interested I have screenshots from my profiling that I can pull up. I might submit these with my PR to back up my claims. Kevin -- Founder/CEO Spinn3r.com Location: *San Francisco, CA* blog: http://burtonator.wordpress.com … or check out my Google+ profile <https://plus.google.com/102718274791889610666/posts>
