RFR: JDK-8153203: Remove liveRange.hpp

Jesper Wilhelmsson jesper.wilhelmsson at oracle.com
Thu Mar 31 18:08:41 UTC 2016


Hi Bengt,

Nice cleanup!

The comment in psMarkSweepDecorator.cpp:294 is slightly confusing: "The first 
dead object should contain a pointer to the first live object"

Does it mean "The first object is dead and should contain a pointer to the first 
live object"?

Besides that the change looks good.
/Jesper


Den 31/3/16 kl. 17:46, skrev Bengt Rutisson:
>
> Hi everyone,
>
> Could I have a couple of reviews for this change?
>
> http://cr.openjdk.java.net/~brutisso/8153203/webrev.00/
> https://bugs.openjdk.java.net/browse/JDK-8153203
>
> The methods CompactibleSpace::scan_and_forward() and
> PSMarkSweepDecorator::precompact() are more or less copy-paste versions of each
> other. Both these use the LiveRange class.
>
> The LiveRange class is used to write to the mark word of a dead object. But no
> one really cares that the LiveRange class is used. Instead it just gives an
> extra level of indirection to already complicated code. We also do unnecessary
> work to keep track of the end of the range even though no one ever gets the end
> value.
>
> We also do duplicate stores to _first_dead in these methods.
>
> The methods that consume the values from the LiveRange
> (CompactibleSpace::scan_and_adjust_pointers() and
> PSMarkSweepDecorator::adjust_pointers()) don't use the LiveRange class. Instead
> they use oop()->mark()->decode_pointer(), which is kind of odd considering that
> this is normally used for forwarded objects.
>
> The code would be simpler if we just store and load directly from the memory
> addresses we are working with.
>
> Improving the assert at the end of the
> CompactibleSpace::scan_and_adjust_pointers() and
> PSMarkSweepDecorator::adjust_pointers() methods to log the values of q and
> prev_q will hopefully improve the chances of understanding JDK-8073321 if that
> ever happens again.
>
> Thanks,
> Bengt


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