Re: [mat-dev] GarbageCleaner phase code

[Andrew Johnson <andrew_johnson@xxxxxxxxxx>]

> Hi all,
> 
> Looking for some input on suitability to raise a bug and submit this
> change. If you can advise any additional specific tests to run I 
> will be happy to build them out and execute them..
> 
> Results on a 73GB file over 5 runs on a 48GB 8+8cores machine are 
> here, in brief it is 2-4x faster for large heaps:
> https://gist.github.com/jasonk000/9f31e2446a84b56f11d494c146969e7b
> 
> I understand that my last round of commits required an additional 
> pass of discussion on memory footprint. I believe the memory 
> footprint here would be reduced as it merges the maps during 
> generation (C maps, scaling to C cores) vs previous approach (N 
> maps, when the processing was split into N chunks and scaled to 
> object heap). All existing functional tests work ok.
> 
> There are a sequence of five commits presented here:
> https://github.com/jasonk000/eclipse-mat/compare/gc-opt
> 
> Thanks
> Jason_______________________________________________

This looks like a useful improvement. I don't have any tests in mind, 
but do look at the previous changes to GarbageCleaner.java and what
defects led up to the change.

Tests are useful, but with multi-threaded code then reviews of the
code are also important as defects will not be as reproducible.

For example the change to
if (ref != null && ref.get() != null)
{
    return ref.get();

could cause problem as the soft reference could be cleared between
the two get() calls.

Sometimes a test mode - with more threads or large / smaller
buffers, or a constrained heap, or a very large heap dump with
nearly 2G objects can help find bugs.

Do other people have comments?

Andrew Johnson

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