RFR(S): 8216426: Usage of array placement new may lead to memory corruption

[Kim Barrett]

> On Jan 14, 2019, at 11:39 AM, Doerr, Martin <martin.doerr at sap.com> wrote:
> 
> Hi,
>  
> thanks for looking at this issue and especially for adding comments.
> Sounds like this issue should better get fixed although there are no known problems.
>  
> Should we fix it by replacing the array placement new by normal placement new for each element?
> http://cr.openjdk.java.net/~mdoerr/8216426_array_placement_new/webrev.00/
>  
> Best regards,
> Martin

Looks good.

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src/hotspot/share/utilities/concurrentHashTable.hpp
  76   // Only constructed with placement new from an array allocated with MEMFLAGS
  77   // of InternalTable.

Given this comment, I'm tempted to suggest making the constructor
private and having a public "static Bucket* make_array(size_t size)"
function.  Then remove the comment... But I'm not going to require
such a change to pass review.

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src/hotspot/share/utilities/concurrentHashTable.inline.hpp
 196   _buckets = (Bucket*)NEW_C_HEAP_ARRAY(Bucket, _size, F);

No cast needed here.  NEW_C_HEAP_ARRAY(T, ...) returns T*.

I don't need another review for just this change.

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