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From "Vera Volynets (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HARMONY-881) DRLVM GC heap verification infrastructure
Date Fri, 11 Aug 2006 11:04:15 GMT
    [ http://issues.apache.org/jira/browse/HARMONY-881?page=comments#action_12427500 ] 
Vera Volynets commented on HARMONY-881:

I would like to introduce you a small feature to GC heap verification infrastructure. 
It is also hijacked into GC-VM interface.
After gc initialization functions concerning write barriers are hijacked and all write operations
are recorded in array which I called heap mirror.

During first heap traversal content of heap mirror is compared with gc heap.  So the right
usage of write barriers is verified. 

At this moment my code triggers verification failure, but I couldn't find out what causes
this failure. I observed verification failure on tests stress.Finalizer and stress.Mix. The
reason of failure can be either in my code or in vm, because to this very day only stop-the-world
collector was used, so implementation and usage of write barriers were not properly verified.
I rely on you participation to find the reason of failure.

To use this patch patches "Enable GC write barriers in DRLVM" HARMONY-504 and two patches
from "DRLVM GC heap verification infrastructure" HARMONY-881 should be applied first.

Also this feature works only with interpreter enabled:
To turn on this feature:

See attached file: 0003-Checks correctness of write barriers work.txt

> 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
> *************   GC heap verification infrastructure   *************** 
> Hi,
> 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.
> *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
> - 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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