[mvt] RFR - add support for q-types in lambda forms

Paul Sandoz paul.sandoz at oracle.com
Mon Jun 5 18:20:21 UTC 2017


One thing that concerns me about BMHs and Species is the possible combinatorial explosion if we have to create specific Species classes to hold values. At the moment the method handle internals operate on five basic types (L, I, J, F and D).

What should the type of a Species field that holds a value augment which:

1) avoids boxing to Object; and

2) avoids a possible combinatorial explosion.

?

Is there an intermediate carrier type we can use has less baggage than Object?

Paul.

> On 5 Jun 2017, at 10:56, Karen Kinnear <karen.kinnear at oracle.com> wrote:
> 
> The top value wrapper type today is sort of a marker type - i.e. you can not instantiate one, and in MVT
> you can currently use it in either a method signature or for vreturn.
> 
> If you have other required uses - please let us know - we are working on how much we need to expose this in the JVMS draft.
> 
> thanks,
> Karen
> 
>> On Jun 5, 2017, at 1:46 PM, Paul Sandoz <paul.sandoz at oracle.com> wrote:
>> 
>> Hi Remi,
>> 
>> Yes thanks for clarifying, which simplifies things API-wise and makes sense in hindsight when considering just primitives.
>> 
>> I am still getting to grips with this Q-type stuff, excuse my ignorance. The top value wrapper type (currently __Value) is sort of a box or carrier, but one without identity with immutable contents and the VM can single them out for optimisation. Correct?
>> 
>> Paul.
>> 
>>> On 3 Jun 2017, at 06:56, Maurizio Cimadamore <maurizio.cimadamore at oracle.com> wrote:
>>> 
>>> 
>>> 
>>> On 03/06/17 12:51, Remi Forax wrote:
>>>> Hi Paul, Hi Maurizio,
>>>> bindTo() or insertArguments use the corresponding types from the method type to unbox the argument if necessary,
>>>> so actually bindTo(3) will insert 3 and not the boxed Integer if the corresponding type is an int.
>>>> 
>>>> The same way, a boxed value type can be unboxed if the corresponding type is a Q-type,
>>>> so there is no need of a bindTo(__Value).
>>>> 
>>>> In term of performance, this is not an issue because neither bindTo() nor insertArguments() should be called on a fast path.
>>> Yeah - thanks for the clarification - this corresponds to my understanding of the model - that is, with BMH, boxing happens 'at the boundaries', when you set up the method handle chain - but I think that in order to get there you need at least to teach BMH about value types (that is, the Species_XYZ classes should have methods to construct bound versions with value types), otherwise the chain will just get boxed to Object internally.
>>> 
>>> Maurizio
>>>> 
>>>> regards,
>>>> Rémi
>>>> 
> 



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