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

[Coleen Phillimore]

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