Sorry, one more point I forgot to mention:
3) what impact will this have, if any, on register allocation when a ref's
lifetime is artificially extended without any "real" use. The thinking
here is compiler should spill it and never reload, but it was unclear if it
will do the right thing in its current form.
sent from my phone
On Dec 11, 2015 10:52 AM, "Vitaly Davidovich" <vita...@gmail.com> wrote:
> Hi Paul,
>
> No objections, but just wanted to summarize a couple of possible key
> performance issues that were raised on the concurrency-interest thread.
> You may have picked them up already, so pardon the repetition:
>
> 1) current impl/prototype is purposely barred from inlining - this will be
> a compiler optimization fence, particularly bad in loops
>
> 2) the expected "try { ... use(r) ... } finally { reachabilityFence(r);
> }" idiom will significantly increase bytecode size, possibly impacting
> inlining.
>
> I'm sure you guys will address this in the end, but just wanted to
> reiterate those just in case :).
>
> Thanks
>
> sent from my phone
> On Dec 11, 2015 4:37 AM, "Paul Sandoz" <paul.san...@oracle.com> wrote:
>
>> Unless any strong objections are raised I plan to push the latest path on
>> Monday.
>>
>> >
>> > Updated:
>> >
>> >
>> http://cr.openjdk.java.net/~psandoz/jdk9/JDK-8133348-reachability-fence-jdk/webrev/src/java.base/share/classes/java/lang/ref/Reference.java.sdiff.html
>> <
>> http://cr.openjdk.java.net/~psandoz/jdk9/JDK-8133348-reachability-fence-jdk/webrev/src/java.base/share/classes/java/lang/ref/Reference.java.sdiff.html
>> >
>> >
>> > I think there is an opportunity to add further examples, but i would
>> like to take a swing at that later on.
>> >
>> >
>> >> - I now agree with you and Doug about calling this a "fence". Can we
>> >> just name it "fence" rather than the wordier "reachabilityFence"?
>> >> Looking at a typical invocation,
>> >>
>> >> Reference.reachabilityFence();
>> >>
>> >> seems a bit redundant while
>> >>
>> >> Reference.fence();
>> >>
>> >> reads quite nicely. Is there, or will there ever be, any other kind
>> >> of reference-related fence?
>> >>
>> >
>> > I doubt there will be another kind of reference fence, but it could be
>> used in conjunction with other memory fences (currently on VarHandles) and
>> if static imports are used it might look rather out of place as to what
>> fence “fence” actually refers to. That is why i prefer the longer more
>> descriptive name.
>> >
>> > Paul.
>>
>>
