Brilliant idea. I will do more experiment.
Thanks
Max
> On Feb 23, 2018, at 11:25 AM, Xuelei Fan <xuelei....@oracle.com> wrote:
>
> 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
>>>
