RFR 8140685: Fix backtrace building to not rely on constant pool merging

[Coleen Phillimore]

On 11/2/15 3:43 AM, serguei.spitsyn at oracle.com wrote:
> Hi Coleen,
>
>
> The fix looks good to me.
> I like the simplifications!
>
>
> A minor comment:
>
> src/share/vm/classfile/backtrace.hpp
>
> 34 // doesn't get deallocatd.
>
>   typo: deallocatd => deallocated

Thank you Serguei for reviewing this.  I thought you'd like the 
simplification after all the work we've done on this.

I fixed the typo above.

Coleen
>
>
> Thanks,
> Serguei
>
>
> On 10/30/15 15:16, Coleen Phillimore wrote:
>>
>> On 10/30/15 6:01 PM, Coleen Phillimore wrote:
>>> Summary: Save Throwable in a list which is a weak GC root for 
>>> walking during MetadataOnStackMark
>>>
>>> This was the original implementation that I had for finding Method* 
>>> in backtraces but it was slow because I had used jweak to save the 
>>> Throwable object.   Using internal vm weak GC roots, this does not 
>>> cause a performance regression in refWorkload.  This fix is more 
>>> straightforward and does not rely on the constant pool index of the 
>>> merged constant pool during redefinition to find the method's name.
>>> This is one fix that enables removing merged constant pools during 
>>> redefinition (work in progress).  It also is would be used as a 
>>> model for JEP 259: Stack Walking API
>>> https://bugs.openjdk.java.net/browse/JDK-8043814.
>>>
>>> The code that registers MemberNames for replacing Method* during 
>>> redefinition may need to use the same mechanism for performance, if 
>>> MemberName arrays are used for the Stack Walking API.
>>>
>>> I assume this will generate comments from the GC group.
>>>
>>> bug link https://bugs.openjdk.java.net/browse/JDK-8140685
>>>
>>
>> open webrev at http://cr.openjdk.java.net/~coleenp/8140685.01/
>> bug link https://bugs.openjdk.java.net/browse/JDK-8140685
>>
>>>
>>> Tested with RBT quick (former "quick" tests), 
>>> jdk/java/lang/instrument tests and the test that I wrote for 
>>> handling backtraces with redefinition in 
>>> hotspot/test/runtime/RedefineTests.
>>>
>>> Thanks,
>>> Coleen
>>
>