S RFR: 8010783: assert(s->refcount() !=0) failed

[Karen Kinnear]

Dan,

Thank you for the quick review. I updated the bug to answer the concern you brought up
from Vladimir.

To repeat it here:

Default methods are new with JDK8. They are concrete methods in interfaces.
The intention is to be able to expand existing interfaces with new methods, without 
requiring recompilation of older classfiles. If any supertype has a default method, then
you will check for defaults in a given class in order to apply the new inheritance rules
for concrete methods in interfaces, which are designed to prevent multiple inheritance -
i.e. any method defined in a superclass wins, otherwise if there is a unique most-specific
default method you use that. Any ambiguity throws and error when you try to reference it.

I put some of the highlights of the call stack in the bug report.

As javac, the lambda metafactory and the addition of lambdas and new default methods
in our libraries change rapidly in the near future, the vm will be processing more and more
default methods.

hope this helps,
Karen

On May 1, 2013, at 3:42 PM, Daniel D. Daugherty wrote:

> On 5/1/13 1:26 PM, Karen Kinnear wrote:
>> Please review for lambda:
>> 
>> http://cr.openjdk.java.net/~acorn/8010783/webrev/src/share/vm/classfile/bytecodeAssembler.cpp.sdiff.html
> 
> src/share/vm/classfile/bytecodeAssembler.cpp
>    Swapping the order of the 'symbol_at_put()' and 'increment_refcount()'
>    calls is simple enough. That should make this assert() happy:
> 
>    src/share/vm/oops/constantPool.hpp:
>    308    void symbol_at_put(int which, Symbol* s) {
>    309      assert(s->refcount() != 0, "should have nonzero refcount");
> 
>    by making sure the entry is marked as in-use before it is 'put'
>    somewhere.
> 
>    However, Vladimir's comment and the stack trace in the bug report
>    made me wonder if we were doing some default method processing on
>    classes that didn't need it. Perhaps there are two issues here?
> 
> Thumbs up, if we don't have two bugs here.
> 
> Dan
> 
>> 
>> Passes test in bug report for fastdebug: java -XX:+CompileTheWorld -XX:+CompileTheWorldStartAt=12
>> -Xbootclasspath/p:interclient-core.jar
>> 
>> vm.quick.testlist, lang, vm jck's in progress on on linux-x64
>> 
>> thanks,
>> Karen