RFR: Clear outgoing matrix for root regions during preparation phase

[Aleksey Shipilev]

On 03/22/2017 04:16 PM, Roman Kennke wrote:
> We're currently clearing the outgoing matrix for root regions during the
> collection phase of partial GC. I find it more natural to do it in the
> preparation phase. While it's not per-se incorrect (only one thread
> should have to do with each root region at a time), I'm a bit uneasy to
> have threads clearing whole rows, while other threads are updating the
> matrix. They *should* not collide, but I'll sleep better if we could
> just do it during preparation. It also means to move verification up
> before preparation, because otherwise whole rows will be cleared.
> 
> http://cr.openjdk.java.net/~rkennke/cleanmatrix/webrev.00/

Yes, I was wondering about the same. Looks good.

-Aleksey