Can we also get some feedback on specialization, please?

Palo Marton palo.marton at gmail.com
Sat Jan 10 21:01:40 UTC 2015


CHM will prevent class unloading and that can be a problem for long running
server.

On Saturday, January 10, 2015, Peter Levart <peter.levart at gmail.com> wrote:

>
> On 01/10/2015 10:58 AM, Remi Forax wrote:
>
>>
>> On 01/10/2015 04:49 AM, Brian Goetz wrote:
>>
>>> You might look at ClassValue as a means for this sort of per-class
>>> static constants?
>>>
>>
>> The result of ClassValue.get() with a constant class is not a constant at
>> least with the current implementation.
>>
>> Rémi
>>
>
> The alternative is to use the class literal as a key into CHM for example:
>
> class HolderClass<any T> {
>     static final ConcurrentMap<Class<?>, X> constants = new CHM<>();
>
>     static <any T> X getConstant() {
>         return constants.computeIfAbsent(HolderClass<T>.class, (c) -> {
> ... });
>     }
>
>
> See also here, when you know the values for all specializations upfront:
>
> http://cr.openjdk.java.net/~plevart/misc/valhala-hacks/util/AnyHelper.java
>
>
> Regards, Peter
>
>
>>
>>> On 1/9/2015 10:47 PM, MacGregor, Duncan (GE Energy Management) wrote:
>>>
>>>> And another thing...
>>>>
>>>> If I want to try and combine the use of VarHandles and specialisation
>>>> to make something with atomic properties (as I'm sure we'll all want
>>>> to do for concurrent collections) then at the moment I can't use
>>>> static fields for the var handles, and the JIT is almost certainly
>>>> going to hate me if I they are stored on instance fields. I think
>>>> we'll need some way to specify static fields as specialised and
>>>> provide initialisers for them. This cannot be done by simply having
>>>> different statics for different layers since each specialised class
>>>> will need it's own statics.
>>>>
>>>> I'm sure there's also some evil I can perpetrate by specialising
>>>> CallSites, but I haven't though of a really convincing case for doing
>>>> so yet (at least not until I can define typed tuples when I can maybe
>>>> replace various varargs fallbacks), and I hit the same statics
>>>> problem as above with MethodHandles anyway.
>>>>
>>>
>>
>


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