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

[serguei.spitsyn at oracle.com]

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


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
>