RFR (M): 8217778: StringTable cleanup miscalculates amount of dead objects

[Thomas Schatzl]

Hi again,

  cc'ed hotspot-runtime-dev since it concerns the string table.

Also, this patch is based on the changes for JDK-8213229.

Thanks,
  Thomas

On Mon, 2019-01-28 at 12:43 +0100, Thomas Schatzl wrote:
> Hi all,
> 
>   can I have reviews for this change that tries to fix the issue with
> the string table reporting too low "dead" numbers to the
> ServiceThread notification mechanism in the review for JDK-8213229,
> potentially causing C heap memory being kept live for longer than
> necessary?
> 
> This change implements one option for fixing this, in particular that
> the WeakProcessor calls OopStorage::oops_do() instead of
> ::weak_oops_do, counting the number of NULL entries manually.
> 
> There is another, let weak_oops_do() return the number of NULL
> entries as function return value. However the return value of the
> used iterate_safepoint() is already in use in some I'd consider
> interesting test case. I did not want to add another out-parameter
> either.
> 
> Since the WeakProcessor has been the main user of the weak_oops_do()
> method, I would suggest to clean this up preferably in an extra CR:
> there is still one use of the OopStorage::weak_oops_do() method that
> could be easily removed. If you think we should not remove it, I
> strongly suggest to rename the weak_oops_do() methods to better
> indicate what they actually do instead of giving a very strong
> (wrong) suggestion where/when they should be used.
> 
> CR:
> https://bugs.openjdk.java.net/browse/JDK-8217778
> Webrev:
> http://cr.openjdk.java.net/~tschatzl/8217778/webrev/
> Testing:
> hs-tier1-5
> 
> Thanks,
>   Thomas
> 
>