Hi Weijun,
I thought more about the performance impact. The impact may mainly come
from the big size of the cached entries.
The current implementation needs to go over the full list: find the 1st
expired item and then remove the rest. The previous one have an
additional round with entries.indexOf(). Could we just start from the
end of the list?
while (true) {
E e = entries.removeLast();
if e not expired {
add it back and break;
}
};
If the list is really big, and the lifetime is significant big as well
(>> 1 minute), iterate from the oldest item (backward from the end of
the list) may be much more effective. LinkedList itself is not
synchronized, so as if there is not too much items to go over, the
performance should be fine. I'm hesitate to hard code a cleanup every 1
minute strategy. If we clean often, there may be not too much items to
go over in the list. So we might be able to remove the "at most every
minute" strategy.
Xuelei
On 2/22/2018 5:55 PM, Weijun Wang wrote:
Updated webrev at http://cr.openjdk.java.net/~weijun/8197518/webrev.01/.
On Feb 23, 2018, at 9:02 AM, Weijun Wang <weijun.w...@oracle.com> wrote:
You mean I can save it somewhere and only update it when a cleanup is performed?
This should be better. Now there will be only isEmpty(), getFirst() and
addFirst(), and one less getLast().
Thanks
Max
On Feb 23, 2018, at 1:45 AM, Xuelei Fan <xuelei....@oracle.com> wrote:
Looks like list synchronization is a factor of the performance impact. Maybe, you can
have a private time for the oldest entry so don't access/iterate/cleanup entries list
until necessary. The "at most every minute" may be not a good strategy in some
situations.
In fact, it's now almost "exactly every minute". What situations do you think
it's not good? I cannot use size() because I have to remember all entries with lifespan
to be correct.
Thanks
Max
Xuelei
On 2/22/2018 12:36 AM, Weijun Wang wrote:
Please take a review at
http://cr.openjdk.java.net/~weijun/8197518/webrev.00/
Two notes:
1. I tried list.subList(here, end).clear() but it's not faster.
2. I have looked at ConcurrentHashMap + ConcurrentSkipListMap but will need
more time to verify its correctness and measure the performance gain. Since the
bug is reported on 8u, a safer fix looks better.
Noreg-perf.
Thanks
Max
