RFR: Clear outgoing matrix for root regions during preparation phase

[Roman Kennke]

Good question. I don't think so, because we'd be messing with the matrix
for regions we're likely to look at. While it probably wouldn't clash, I
find it easier to convince myself if it happens in a separate pass.
That's why I hooked it up on the last pass.

Roman

Am 22.03.2017 um 16:35 schrieb Zhengyu Gu:
> Would it be better to the clear outbound matrix during building the
> root set?
>
> -Zhengyu
>
> On 03/22/2017 11:16 AM, 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/
>> <http://cr.openjdk.java.net/%7Erkennke/cleanmatrix/webrev.00/>
>>
>> Roman
>>
>>