RFR: JDK-8202788: Explicitly reclaim cached thread-local direct buffers at thread exit

[Peter Levart]

Hi Tony, Alan,

On 06/06/2018 04:37 PM, Tony Printezis wrote:
> Alan,
>
> Thanks for your thoughts!
>
> Peter,
>
> Any chance of taking the two suggestions I made in an earlier e-mail 
> into account?

Right, I'll prepare new webrev with that shortly.

>
> a) It’d be nice if users can override initialValue(), like when using 
> the standard ThreadLocal class, instead of calculateInitialValue(). (I 
> can’t come up with a clean solution on how to do that, though. I’ll 
> think about it for a bit.)

Your concern was that users might accidentally override initialValue() 
instead of calculateInitialValue(), if I understood you correctly. If 
that was the concern, they can't, because it is final. If the concern 
was that users would want to override initialValue() because they are 
used to do so, then perhaps a javadoc on final initialiValue() pointing 
to calculateInitialValue() might help them. Do you agree? This is 
currently internal API and consistent naming is not a big concern.

> b) It’d be very helpful to pass T value to threadTerminated(), as I 
> cannot imagine many use-cases where the value will not be needed.

Agree. Will include that in new webrev.

>
> Re: renaming JdkThreadLocal: ThreadLocalWithExitHooks?

Hm. Exit Hooks are already something that is used in JVM (Threads 
started when VM is about to exit), so this might be confusing for someone.

- DisposableThreadLocal
- ThreadLocalWithCleanup

And my favorite:

- TerminatingThreadLocal


>
> Re: exposing getIfPresent() : Yes! Pretty please! :-) This will be 
> very helpful and can avoid completely unnecessary allocations.

I agree that this would be generally useful functionality. Might be good 
to ask for opinion on concurrency-interest mailing list first. Will do that.

Regards, Peter

>
> Tony
>
>
> —————
> Tony Printezis | @TonyPrintezis | tprintezis at twitter.com 
> <mailto:tprintezis at twitter.com>
>
>
> On June 6, 2018 at 9:38:05 AM, Alan Bateman (alan.bateman at oracle.com 
> <mailto:alan.bateman at oracle.com>) wrote:
>
>>
>>
>> On 30/05/2018 22:16, Peter Levart wrote:
>> > I thought there would be some hint from Alan about which of the two
>> > paths we should take for more refinement.
>> >
>> > The Tony's:
>> >
>> > http://cr.openjdk.java.net/~tonyp/8202788/webrev.1/ 
>> <http://cr.openjdk.java.net/%7Etonyp/8202788/webrev.1/>
>> >
>> > Or the Alan's with my mods:
>> >
>> > 
>> http://cr.openjdk.java.net/~plevart/jdk-dev/DBBCache_Cleanup/webrev.02/ 
>> <http://cr.openjdk.java.net/%7Eplevart/jdk-dev/DBBCache_Cleanup/webrev.02/> 
>>
>> >
>> Finally getting back to this one.
>>
>> I don't think the two approaches are all that different now. Tony's
>> point on the number of hooks vs. number of locals was an important point
>> but with Peter's update to use a thread local registry then I think we
>> have easy to maintain solution in the DBBCache_Cleanup/webrev.02 patch.
>> So I think I prefer that approach. We need to better name for
>> "JdkThreadLocal", something to indicate that it holds resources or it
>> notified when a thread terminates.
>>
>> Also along the way, we touched on exposing getIfPresent and we should
>> look at that again. If it is expose then it fits well with the second
>> approach too.
>>
>> -Alan