RFR: 8185925 & 8153682 (footprint reduction of java.lang.StackFrameInfo)

[Brent Christian]

Hi,

There are a couple opportunities to reduce the memory footprint of 
java.lang.StackFrameInfo (the internal implementation of 
java.lang.StackWalker.StackFrame):

8153682[1] : StackFrameInfo.declaringClass could be removed
8185925[2] : StackFrameInfo::walker field can be replaced with bitmap to 
save footprint

I had a look using jol[3].  Removing only 'walker' helps only under 32- 
and 64-bit, but not with compressed oops.  Removing both 'walker' and 
'declaringClass' brings a benefit to compressed oops as well (though not 
for 16-byte aligned).

The size change, in bytes, for each execution mode is as follows:

                              32-bit: 32->24
                              64-bit: 56->40
                  64/compressed oops: 32->24
64/compressed oops, 16-byte aligned: 32->32

(For reference, the jol reports for the baseline and specimen are at [4] 
and [5], respectively.)

Please review my code change for this.  The webrev is here:
http://cr.openjdk.java.net/~bchristi/8185925/webrev.03/

An automated test run is in progress.

Thanks!
-Brent

--
1. https://bugs.openjdk.java.net/browse/JDK-8153682
2. https://bugs.openjdk.java.net/browse/JDK-8185925
3. http://openjdk.java.net/projects/code-tools/jol/
4. 
http://cr.openjdk.java.net/~bchristi/8185925/StackFrameInfo.jol.baseline.txt
5. 
http://cr.openjdk.java.net/~bchristi/8185925/StackFrameInfo.jol.rmDeclClass.txt