RFR: 8077836: Make sure G1ParGCAllocBuffer are marked as retired

[Thomas Schatzl]

Hi Stefan,

On Wed, 2015-04-15 at 15:08 +0200, Stefan Johansson wrote:
> Hi,
> 
> Please review this fix for:
> https://bugs.openjdk.java.net/browse/JDK-8077836
> 
> Webrev:
> http://cr.openjdk.java.net/~sjohanss/8077836/hotspot.00/
> 
> Summary:
> At the end of a G1 gc a call to G1ParGCAllocator::retire_alloc_buffers 
> is made, in this code we should make sure all alloc buffers are retired. 
> This is currently handle by calling flush_and_retire_stats for each 
> active buffer. Because this method is only implemented for 
> ParGCAllocBuffer and not for G1ParGCAllocBuffer we currently miss 
> updating the _retired field in G1ParGCAllocBuffer.
> 
> The _retired field is checked in a guarantee in the G1ParGCAllocBuffer 
> destructor, but this destructor is not usually called because we are 
> missing a virtual destructor for G1ParGCAllocator.
> 
> This patch adds this destructor and implements 
> G1ParGCAllocBuffer::flush_and_retire_stats by calling the version in 
> ParGCAllocBuffer and setting the _retired field to true.
> 
> Testing:
> Manual verification that G1 always fails with the new destructor and 
> that the fix avoids this.

Looks good. One thing that might be interesting to add for consistency
is to add the early-out like in retire() if the PLAB has already been
retired.
It does not seem to hurt to leave it out, but for consistency it might
be desirable.

Also the change needs to be rebased to the current repository.

Thanks,
  Thomas