nestmates spec open issues

John Rose john.r.rose at
Thu Oct 26 04:03:46 UTC 2017

On Oct 25, 2017, at 8:54 PM, David Holmes <david.holmes at> wrote:
> On 26/10/2017 1:11 PM, John Rose wrote:
>> On Oct 25, 2017, at 8:07 PM, John Rose <john.r.rose at> wrote:
>>> On Oct 25, 2017, at 3:33 PM, Remi Forax <forax at <mailto:forax at>> wrote:
>>>> getClasses() throws an exception but getAnnotations() skips unavailable annotations.
>>>> that said, i'm not against throwing in this case.
>>> I'm not against throwing either, but I think scrubbing (like annotations)
>>> is a little better, because it is more robust about retaining partial results.
> Aren't annotations a different situation because annotations are well known to potentially not be available at runtime? A missing annotation does not necessarily reflect an error in the runtime environment of an application. Also AFAIK see from the jdk/java/lang/annotation/Missing/ test the throw/no-throw behaviour depends on exactly how the missing annotation is used.

I think the most likely cause of a missing nestmate will be JAR minimization.
As long as the nest-host isn't deleted, a dropped nestmate is of no concern,
in that scenario.

This is obviously different from annotations, but is enough like them to
make me think favorably on the scrubbing of lists.  Drop an annotation,
drop a nestmate; both seem to benefit from a fail-over tactic that ignores
the dropped thing, when asking about neighboring things.

>>> Partial results are important if you are just asking about one or two
>>> classes and don't care about their other nestmates.
> How do you know to only ask about "one or two classes"? Sorry I'm not understanding the potential usecase here.If you've already identified specific classes of interest then you can call getNestHost on them.

I'm thinking about code that emulates hasNestMateAccess by
scanning the getNestMembers list.  Perhaps if we have a correctly
functioning hasNestMateAccess, my concern goes away.

>> And even if H.getNestMembers() throws because of some missing N1,
>> we have to be careful to allow N2.getNestHost() to return H, if we can
>> validate that N2 points to H and vice versa.  We don't want the validated
>> relation between N2 and H to be collateral damage to a failure of N1.
> Absolutely not. The two queries would be completely unrelated in that regard.

Yep, good.

>> (If H goes missing there is nothing we can do with N1 and N2, except
>> to assign each to its own 1-nest.  Which is OK with me.)
> Then presumably we should do the same at the VM level instead of allowing resolution related exceptions to propagate as currently proposed? We could just throw IAE as we do if a nest-host validation check fails. Though a case can still be made to allow VME's to pass through.

Please don't throw IAE that case.  I don't want to bikeshed exception types,
but I think we have a strong precedent for using ICCE when encountering
a questionable classfile configuration (one that shouldn't have come out of
javac).  Note also the ICCE <: VME, so it just gets passed through.

> Though I still feel uncomfortable lying about the nest-host. I don't see what usecases would be served by doing that. Other than informational uses, I can't see a reason to actually identify the nest-host which would not be impacted by lying about that identity. The only truly useful query is for nestmate access and that doesn't need to expose the identity of the nest-host and conservatively rejects access if anything goes wrong.

I'm sympathetic to this, but that implies that getNestHost should return null
rather than this for a non-nesty class.  I think it's more valuable that getNestHost
return 'this' for non-nesty classes, and therefore also for broken-nest classes.

> Bottom line for my personal preferences:
> - hasNestMateAccess: never throws, always returns true or false

> - getNestHost(): throw if the host isn't there or else a membership validation check fails
See above.

> - getNestMembers(): throw if any nest member isn't there or a membership validation check fails
As I said before, I don't mind this choice.  Especially if we have hasNestMateAccess.

> Cheers,
> David

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