Can we also get some feedback on specialization, please?

Peter Levart peter.levart at gmail.com
Sat Jan 10 22:16:54 UTC 2015


On 01/10/2015 10:01 PM, Palo Marton wrote:
> CHM will prevent class unloading and that can be a problem for long 
> running server.

In this particular case the specialized classes will be referenced from 
static field of non-specialized class, all of them loaded by same 
ClassLoader and all of them eligible for GC at the same time.

Peter

>
> On Saturday, January 10, 2015, Peter Levart <peter.levart at gmail.com 
> <mailto: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
>     <http://cr.openjdk.java.net/%7Eplevart/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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