[Nestmates] RFR Lookup.defineClass nest-host update

David Holmes david.holmes at oracle.com
Mon Nov 5 21:16:11 UTC 2018

Hi Mandy,

On 6/11/2018 4:52 AM, Mandy Chung wrote:
> Hi David,
> On 11/4/18 11:03 PM, David Holmes wrote:
>> webrev: 
>> http://cr.openjdk.java.net/~dholmes/dynamic-nestmates/webrev.nest_host_update/ 
>> Testing showed that the internal use of Class.getNestHost inside 
>> Lookup.defineClass was not suitable as invalidly defined 
>> nest-hosts/members resulted in an inappropriate nest-host being passed 
>> into the the VM to set_nest_host (a class becomes it's own nest-host 
>> if there are any validation errors). set_nest_host needs a valid 
>> nest-host else we'll hit assertion failures.
>> The solution was to pass the lookupClass through to the VM and have 
>> jvm_lookup_define_class do a direct InstanceKlass::nest_host() lookup 
>> that will throw exceptions if there are validation issues.
> The fix looks fine to me.  The adjusted logging statement reads better, 
> thanks.  Should we add a test for it?

What kind of test, it is just an informational output AFAICS.

> Alternatively  we can keep JVM_LookupDefineClass to expect the lookup 
> class parameter must be the nest host (that's the intent - do you see a 
> check in the VM side to enforce that?).  The library will do the 
> validation and pass a valid nest host to JVM entry point to keep it 
> simple.   In that case perhaps JVM_GetNestHost can take an additional 
> argument with exception or not.   Lois may have an opinion.

I wanted to avoid having to expose a second API to call into the VM to 
get the nest-host but allow for exceptions. This also reduces the number 
of calls into the VM.

Further, all the way through the library code and into the VM the class 
parameter was already called "lookup", but in fact was only non-NULL 
when it was actually the nest-host - which need not be the same as the 
lookup class. At least now the parameter is always non-null and always 
the lookup.


> Mandy

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