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Date: Fri, 11 Aug 2006 04:10:15 -0700 (PDT)
From: "Vera Volynets (JIRA)" <jira@apache.org>
To: harmony-commits@incubator.apache.org
Subject: [jira] Updated: (HARMONY-881) DRLVM GC heap verification
 infrastructure
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     [ http://issues.apache.org/jira/browse/HARMONY-881?page=all ]

Vera Volynets updated HARMONY-881:
----------------------------------

    Attachment: 0003-Checks-correctness-of-write-barriers-work.txt

See comment to this patch above.

> 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
>         Attachments: 0001-Add-function-to-gc-interface.txt, 0002-Checks-correctness-of-gc-work.txt, 0003-Checks-correctness-of-write-barriers-work.txt
>
>
> *************   GC heap verification infrastructure   *************** 
> Hi,
> I have been working on implementing GC heap verification infrastructure for Stop-The-World GC in DRLVM.
> 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 change. 
> It works on Windows and Linux ia32 platforms.
>  
> *Description*
> 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 way.
> 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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