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From "Vera Volynets (JIRA)" <j...@apache.org>
Subject [jira] Created: (HARMONY-881) DRLVM GC heap verification infrastructure
Date Fri, 14 Jul 2006 17:07:21 GMT
DRLVM GC heap verification infrastructure   

                 Key: HARMONY-881
                 URL: http://issues.apache.org/jira/browse/HARMONY-881
             Project: Harmony
          Issue Type: New Feature
          Components: Contributions
            Reporter: Vera Volynets

*************   GC heap verification infrastructure   *************** 
I have been working on implementing GC heap verification infrastructure for Stop-The-World
This infrastructure is intended be used with any stop-the-world GC implementation, conforming
to the GC-VM interface (described in gc.h and vm_gc.h), with only a minor GC-VM interface
It works on Windows and Linux ia32 platforms.
GC heap verification infrastructure is a small module which is hijacked into GC-VM interface.
The main idea is to substitute GC interface function so that necessary information can be
easily collected.
Everybody who is interested in GC development and debugging is invited
to try it, modify files and add their own functionality.
At this moment GC heap verification infrastructure verifies that the structure of object reference
graph stays exactly the same during collection. Therefore, the number of strongly reachable
live objects and live bytes before and after GC should stay unchanged.
The verification is performed in two phases:
1) On the start of Stop-The-World phase, all enumerated roots to GC by VM are cached by GC
heap verification infrastructure and heap is traversed, constructing heap "fingerprint", recording
the order of the objects and counting their number and size.   
2) After actual garbage collection is complete, before resuming user threads, the heap is
traced once again and the heap structure is verified. 
*Patch contents*
This is an individual contribution, and it was prepared according to the requirements of Apache
cleanroom process; the size of two files all in all is about 30kb (161 and 585 lines). 
-Patch Add-function-to-gc-interface.txt
It adds function gc_add_finalizable_root_set_entry() for separate counting of finalizable
objects because the GC may not preserve ordering of finalizable objects, and thus the heap
structure can be changed.
-Patch Checks-correctness-of-gc-work.txt
The heart of this patch is file gc_debug.cpp.
The tracing of heap starts with debug_gc_trace_heap() function.
*Users guide*
The debugging mode is off by default, and has no impact on the GC performance.. 
- To turn on GC Debug infrastructure use VM with -Dvm.verify.gc=true option in command line.
- To see debug information build VM in debug mode, BUILD_CFG=debug, and use logger in usual
When enabled, the verification heap trace takes quite a bit of time (two times for each collection:
before and after actual collection), GC pauses increase by 1.5-2 times (from 1406ms to 2515ms)
when running Eclipse on DRLVM built in debug configuration.   

To apply patch: 
patch -p1 < 000*.txt

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