[Nestmates] RFR: 8187768 and 8189940 - nest host resolution and exceptions

David Holmes david.holmes at oracle.com
Tue Oct 31 21:23:48 UTC 2017

As I need to move on I'll push these changes today even though no one 
has had an opportunity to provide feedback.


On 30/10/2017 11:24 AM, David Holmes wrote:
> On 27/10/2017 6:04 PM, David Holmes wrote:
>> Combined webrev: http://cr.openjdk.java.net/~dholmes/8187768/webrev/
>> bug: https://bugs.openjdk.java.net/browse/JDK-8187768
>> 8187768: [Nestmates] Improve exception information related to 
>> bad/missing nest-host class
>> This work implements the latest specification proposal for nest-host 
>> resolution and validation exceptions:
>> http://cr.openjdk.java.net/~dlsmith/nestmates.html
>> and also provides better diagnostic information for the exceptions 
>> that occur. Key features:
>> - instanceKlass::nest_host():
>>    - passes through most resolution related exceptions
>>    - replaces NoClassDefFoundError with a  new NCDFE with the original 
>> as the cause and a message "Unable to load nest-host class of %s" to 
>> give context to the exception
>>    - throws IllegalAccessError when nest membership validation fails 
>> (as per updated spec) with appropriate error message
> I realized that nest_host() should only throw IllegalAccessError when 
> called from has_nestmate_access_to(). I'll address that when adding the 
> reflection API support.
> David
> -----
>> - Reflection::verify_field_access can now more obviously result in 
>> pending exceptions
>> - All callers of Reflection::verify_field_access watch for pending 
>> exceptions and don't replace them with their own IllegalAccessErrors.
>> - runtime/Nestmates/membership tests have been completely rewritten to 
>> test updated spec - including the need to test for failures in the 
>> calling class's nest-host resolution and in the target class's 
>> nest-host resolution.
>> While working here I rediscovered the Xcomp problem where the JIT 
>> tries to load a nest-host class when not allowed to:
>> bug: https://bugs.openjdk.java.net/browse/JDK-8189940
>> 8189940:  [Nestmates] VM Compiler thread needs to load nest-host class!
>> The fix here was to check in InstanceKlass::nest_host() if we are on a 
>> thread that can't call java, and that we may have to load a nest-host 
>> class. In that case we return NULL, causing has_nestmate_access_to to 
>> return false, it's callers post IllegalAccessError and the JIT sees 
>> that failure and falls back to going through the interpreter to 
>> complete its work.
>> runtime/Nestmates tests all pass in normal and Xcomp mode now.
>> Thanks,
>> David

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