Multiple this$1 fields when mixing subclassing and inner classes

[David Holmes]

On 11/09/2019 10:30 pm, Stefan Reich wrote:
> I'm thinking about becoming a JCP member to turn this idea (merging 
> this$x fields) into a JSR.

This doesn't require a JSR, nor do you need to become a JCP member.

This is just an enhancement request for the hotspot implementation 
(assuming it is actually valid, viable and worthwhile).

To work on this all you need to do is become an OpenJDK contributor:

http://openjdk.java.net/contribute/

If the issue is large enough then it may warrant a Java Enhancement 
Proposal (JEP):

https://openjdk.java.net/jeps/1

David
-----

> The JCP paperwork seems scary though, and I don't speak their 
> programming language (legalese) enough to really get what is demanded... 
> https://jcp.org/aboutJava/communityprocess/JSPA2.pdf
> 
> It seems I could become a JCP member as an individual without having to 
> pay a fee. Not sure what all the "IP" fuss is about. "Are you willing 
> and able to sign the JSPA and license IP"? License MY IP to Oracle? Or 
> the other way around? Who can help me out there?
> 
> Greetings
> 
> On Tue, 10 Sep 2019 at 01:30, Stefan Reich 
> <stefan.reich.maker.of.eye at googlemail.com 
> <mailto:stefan.reich.maker.of.eye at googlemail.com>> wrote:
> 
>     Oh, I didn't know about those JDK 11 changes. That may in fact break
>     the idea of merging the references. I'm sure it can still be done,
>     but might require a spec change. And who's gonna pay for that?
> 
>     :-D
> 
>     Thanks
> 
>     On Tue, 10 Sep 2019 at 01:17, David Holmes <david.holmes at oracle.com
>     <mailto:david.holmes at oracle.com>> wrote:
> 
>         On 10/09/2019 9:09 am, Stefan Reich wrote:
>          >     But you're not talking about bytecode here you're talking
>         about inside
>          >     the VM. If there is an invokespecial on this$1 of type A
>         then the
>          >     constant pool lookup of its type will be A and we will
>         resolve the call
>          >     based on A's methods. If it were of type B then the
>         resolution process
>          >     would be different. There's nowhere to "insert a cast" here.
>          >
>          >
>          > Can invokespecials on this$0/this$1 happen? I'm struggling to
>         imagine a
>          > case for this.
>          >
>          > invokespecial invokes private instance methods, superclass
>         methods or
>          > constructors. Superclass methods don't apply, neither do
>         constructors.
>          > And calls to private methods happen through bridges (just
>         verified this
>          > for myself again :):
>          >
>          >        13: aload_0
>          >        14: getfield      #1                  // Field
>         this$0:Lbla;
>          >        17: invokestatic  #4                  // Method
>          > bla.access$000:(Lbla;)V
>          >
>          > So what remains?
> 
>         This changed in JDK 11 with the addition of nestmates. Now inner
>         classes
>         have direct private access, no bridges needed, and we use
>         invokespecial
>         or invokevirtual as appropriate. For private methods
>         invokevirtual is
>         mainly used now, but of course we don't do virtual dispatch -
>         there are
>         special rules for private method resolution and selection.
> 
>         class A {
>             void m() {}
>             class InnerA {
>               void callM() { m(); }
>             }
>         }
> 
>            void callM();
>               descriptor: ()V
>               flags: (0x0000)
>               Code:
>                 stack=1, locals=1, args_size=1
>                    0: aload_0
>                    1: getfield      #1                  // Field this$0:LA;
>                    4: invokevirtual #13                 // Method A.m:()V
>                    7: return
>                 LineNumberTable:
>                   line 4: 0
> 
>          >     BTW what introspection tool did you use to show this?
>          >
>          > My own tools ("JavaX")... here's the example program:
>          > http://code.botcompany.de/1025166
> 
>         Thanks for the pointer.
> 
>         Cheers,
>         David
> 
>          > Many greetings :)
> 
> 
> 
>     -- 
>     Stefan Reich
>     BotCompany.de // Java-based operating systems
> 
> 
> 
> -- 
> Stefan Reich
> BotCompany.de // Java-based operating systems